Ocular Anatomy Flashcards
Telecanthus
abnonrally increased distance between the medial canthus of the eyelids.
Skin layer of eyelid
◦ Contains fin hairs, sweat glands, and sebaceous glands. Thinner skin in the body and contains no fat
SubQ areolar layer of eyelid
◦ Loose CT, lies between the outer skin and underlying orbicularis. Contains the levator aponeurosis in the upper lid.
Orbital portion of the orbicularis oculi
attaches at orbital margins and extends outward. Used for forced closure of eyelids
Palpebral portion of the orbicularis oculi
spontaneous and reflex blinking
• Muscle of Riolan (pars ciliaris)
◦ Roll, tide divide: rotates the eyelashes, keeps lid margins tightly applied to the globe, and divides lashes into anterior/posterior (Gray line is the most anterior portion, surgical landmark during lid repair)
• Muscle of Horner: pars lacrimalis
◦ Fibers from the orbicularis that encircle the canaliculi and help drain tears into the lacrimal sac
SubM areolar layer of eyelid
◦ Thin layer of loose CT that lies between the orbicularis and the orbital septum. Contains the orbital portion of the main lacrimal gland. Peripheral and marginal arcades contained in this layer
Orbital septum
◦ Dense irregular CT that serves as a barrier to the orbit in the upper and lower eyelids. Prevents fat from falling down onto the lid margins and keeps infections localized to the anterior portion of the eyelid
◦ periorbita: continuous with dura of the ON
◦ Orbital septum: continuous with the periorbita and periosteum of the skull. Attaches medial to the lacrimal crest. Lacrimal sac is anteiror to this attachment meaning the orbital septum does NOT protect the lacrimal sac from infection.
◦ Superior septum served as insertion sight for the levator aponeurosis.
Preseptal cellulitis
infraction that occurs anterior to the orbital septum. Orbital cellulitis is an infection that occurs posterior to the orbital septum.
Posterior muscular layer of the eyelid
Superior levator palpebrae muscle and the superior (Muellers) and inferior tarsal muscles.
Superior levator palpebral muscle originates from
Lesser wing of sphenoid
Levator innervated by
CN III
Whitnalls ligament
serves as a fulcrum and changes the course of the levator muscle from anterior-posterior to superior-inferior, allowing it to perform its function
Course of the levator
shortly after reaching whitnalls ligament, the levator muscle extends into the eyelid as a fan shaped tendon known as the levator aponeurosis. The tendon fibers anteriorly through the orbital septum to attach to the skin and the anterior surface of the tarsal plate, forming the superior palpebral fissure
Lateral horn of the levator aponeurosis
travels across the lacrimal gland and attaches to whitnalls ligament. The medial horn merges with the medial palpebral ligament
Superior palpebral furrow
formed by the insertion of the levator aponeursis into the skin of the upper eyelid. The inferior palpebral furrow is formed by the indirect attachment of the inferior rectus muscle into the skin of the lower eyelid. The eyelid furrows separate the tarsal and orbital portions of the eyelid
Muscle of muller innervation
‣ Smooth muscle (a2 receptor) that is innervated by sympathetic pathways. AKA superior tarsal muscle
Muscle of muller originates
on the levator and extends into the tarsal plate. It widens the palpebral fissure 1-3mm of the upper eyelid (minor retractor)
Inferior mullers
originates from the fascial sheath of the inferior rectus and extends onto the tarsal plate.
CN ____ opens the eye and CN ____ closes the eye
III
VII
Tarsal plate
◦ Dense irregular CT that provides rigidity to the eyelid. Horizontal and vertical collagen fibers that surround meibomian glands
‣ Meibomian glands: very large sebaceous glands that are located posterior to the eyelash follicles within the tarsal plate.
◦ Upper and lower tarsal plate meet to make medial (maxillary bone) and laterally (whitnall’s ligament) palpebral ligaments.
Where are meibomian glands located
very large sebaceous glands that are located posterior to the eyelash follicles within the tarsal plate.
Palpebral conjunctiva epithelial layer
extends into fornices and contains goblet cells that produce the mucin layer of tear film. Goblet cells found most in the inferonasal fornix and on the bulbar conjunctiva
Palpebral conjunctiva stroma
loose vascularized CT composed of superficial lymphoid layer and a deep fibrous layer
Superficial palpebral conjunctiva stroma
immunologically active. IgA, macophages, PMNs, mast cells, and eosinophils
Deep layer of the palpebral conjunctiva stroma
connects the conjunctiva to the underlying internal structures . Contains accessory lacrimal glands, nerves and blood vessels of eyelids
The palpebral conjunctival stroma is continuous with
dense CT of the tarsal plate.
Meibomian glands
enormous sebaceous glands within the tarsal plate that open along the lid margins just posterior to the eyelash follicles. Produce the anterior lipid layer of the tears. 25 glands in the upper lid and 20 in the lower lid.
Glands of zeiss
modified sebaceous glands associated with eyelash follicles (usually 2 zeiss glands per eyelash). They lubricate the eyelashes to prevent them from becoming brittle.
Glands of moll
modified apocrine glands located near the lid margin. They empty their contents onto eyelash follicles, zeiss glands, and the lid margin.
Glands of Krause
accessory lacrimal glands that are located in the fornices of the conjunctiva. They are considered merocrine glands and secrete fluids of the same composition as the main lacrimal gland. Krause in crease
Glands of wolfring
accessory lacrimal gland that are larger and less numerous than the glands of Krause. The yare located predominately in the tarsal conjunctiva.
Holocrine glands
Meibomian and zeiss
Whole cell
Apocrine glands
Moll and goblet cells
Portion of plasma membrane
Merocrine glands
Accessory lacrimal glands
Cell substance
Voluntary motor nerves of the eyelid
zygomatic branch of the facial nerve; innervated the orbicularis oculi
Involuntary motor nerves of the eyelid
sympathetic nervous system innervated the muscle or muller
Sensory nerves of the upper eyelid
Trigeminal
innervated by the frontal (supraorbital and Supratrochlear branches) and lacrimal branches of V1 (ophthalmic nerve)
Sensory nerves of lower eyelid
innervated by the infraorbital and zygomaticofacial branches of V2 (maxillary)
What is special about the infratrochlear nerve
Branches from the nasociliary nerves of V1 and innervated the medial aspect of the upper and lower eyelids
Arterial supply to the eyelids from the ICA
Lateral and medial palpebral arteries
-marginal and peripheral palpebral arcades
Anterior ciliary arteries
provide circulation to the bulbar conjunctiva and the CB; this explains why patients with uveitis can experience circumlimbal injection and decreased aqueous humor production in the involved eye.
External carotid branches that supply the eyelid
facial artery branches off of the external carotid and provides circulation to the superficial areas of the eyelid
Conjunctival lymphatics
- lymphatic vessels are found in the conjunctiva and parallel the veins.
- Lateral lymphatics: drain into the parotid (preauricular) lymph nodes
- Medial lymphatics: drain into the submandibular lymph nodes.
Preauricular lymphadenoathy occurs in
viral conjunctivitis (classic for EKC), chlamydial conjunctivitis, and dacryoadenitis (among others). Gonococcal conjunctivitis is the only type of bacterial conjunctivitis that presents with preauricular lymphadenopathy. Parinaud’s oculoglandular syndrome presences with significant preauricular AND submandibular lymphadenopathy.
Muscles of the eyebrow innervated by
CN VII
Frontalis muscle
the main elevators of the eyebrows and forehead. Fibers run vertically to raise the eyebrows in a look of surprise or attention
‣ Originate high on the scalp and inserts near the superior orbital rim
‣ The fontalis muscle
‣ is often used to compensate for a ptosis
Corrugator
medial depressor of the eyebrow. Fibers run obliquely and move the medial edge of the eyebrow down and inward for a look of concentration or sorrow
‣ Originates on frontal bone and inserts into the skin above the media leyebrows
‣ Produces the vertical wrinkles of the forehead as an element of facial expression
‣ Helps to reduce sun glare
Concentration and corner
Procerus
medial depressor of the eyebrow. Pulls skin between the eyebrows down for an appearance of menace or aggression
‣ Originates on the nasal bone (bridge of the nose) and inserts on the frontalis muscle between the eyebrows on each side of the midline,
‣ Produces horizontal furrows across the bridge of the nose.
Primary lateral depressor of the eyebrow
Orbicularis oculi
Lacrimal gland
in a fosses on the temporal side of the frontal bone. Divided into orbital and palpebral portions by the tendon of the superior levator muscle. It is an exocrine gland that releases its products vis merocrine secretion
Artery to the lacrimal gland
◦ Supplied by the glandular branches of the lacrimal artery and drained by the lacrimal vein. It contains the ONLY LYMPHATIC vessels of the orbit (drains into the parotid lymph nodes)
Innervation of lacrimal gland
parasympathetic innervation from the lacrimal nerve of the pterygopalatine ganglion of CN VII. Parasympathetic stimulation causes secretion of the aqueous layer of the tears.
◦ Some sympathetic nerve fibers also follow the lacrimal artery to innervate the lacrimal gland
Acute dacryoadenitis
infection or inflammation of the lacrimal gland and can result in acute swelling and discomfort in the upper lateral eyelid. Main causes are staph and sarcoidosis, and mono.
Nasolacrimal drainage system consists of
lacrimal puncta, canaliculi, lacrimal sac, and the nasolacrimal duct
Lacrimal puncta
◦ Located within a ring of CT called the lacrimal papilla. Each puncta in the upper and lower lid drains into a canaliculua
◦ The lacrimal papilla is responsible for keeping the puncta open
Canaliculi
◦ 10mm long tube lined with stratified and pseudostratified epithelium that connects each puncta to the lacrimal sac
◦ Each tube initally runs vertically 2mm, then travels medically 8mm before joining together to form the common canaliculis that enters the lacrimal sac. The angle at which the common canaliculis enters the sac prevents backflow
◦ The muscle or Horner (part of the orbicularis oculi) surrounds the canaliculis. Contracts to assist in tear drainage.
Lacrimal sac
lies within a fossa in the medial orbital wall formed by the posterior lacrimal crest bone and the anterior lacrimal crest of the maxillary bone.
◦ 10-12mm long
◦ Lined with double epithelium with microvilli and goblet cells.
◦ The orbital septum is posterior to the lacrimal sac, making it more susceptible to infections. The check ligament of the medial rectus is also posterior to the lacrimal sac
◦ The medial palpebral ligament (from the medial upper and lower tarsal plate) divides into two sections that attaches in front of and behind the sac, straddling it.
◦ The muscle or Horner also surrounds the lacrimal sac, dividing it into upper and lower sections
Dacryocystitis
an infection of the lacrimal sac. It usually occurs as a result of nasolacrimal duct obstruction
Main causes of dacryocystits
- Child: problem with valve of hasner
- Adult: age related stenosis (involutional)
- Will have unilateral epiphora
Test for NLD obstruction
• I: fluoroscene and five minutes ◦ All NaFL should be gone in 5m ◦ If not, move onto II • II: saline into canaliculi ◦ Push through, if rock rock solid ◦ Make patient choke=broken blockage ◦ Saves from DCR
Nasolacrimal duct
◦ Travels within the nasolacrimal canal that is formed by the posterior lacrimal crest of the maxillary bone and the inferior concha and lies adjacent to the maxillary sinus. It is 15mm Lon and is lined with double epithelium, microvilli, goblet cells. Terminates in the inferior meatus of the nasal cavity
Valve of hasner
◦ Located at the end of the nasolacrimal duct. It prevents back flow of nasal fluids into the lacrimal drainage system
The orbit contains
globe of the eye, the EOMs, the optic nerve, and other smaller nerves, connective tissue, and adipose tissue
AI repsosne against CT and adipose tissue within the orbit. It causes swelling and inflammation of the orbital tissues, leading to proptosis, lid retraction, EOM restrictions, and possible optic nerve compression
Thyroid related ophthalmopathy
Intracanalicular adipose tissue
located WITHIN the muscle cone of the four recti muscles and serves to separate them from the optic nerve
Extraconal adipose tissue
located OUTSIDE the muscle cone between the EOMs and the walls of the orbit.
What is unique about EOMs compared to other muscles
Denser blood supply and nerve supply
Faster movements and more fatigue resistant due to unique combo of red and white fibers
Superior rectus specs
‣ Originates from the common tendionous ring (annulus of Zinn)
‣ 7.7mm from the limbus
‣ The sheath covering the SR is connected to the sheath of the superior levator muscle and the CT of the superior conjunctival fornix. These connections ensure that the lid is raised when the eye is in upgaze.
Inferior rectus specs
‣ Originates from the common tendinous ring
‣ 6.5mm from the limbus
‣ IR sheath combines with the IO sheath to form the supensory ligament of Lockwood. It attaches to the inferior tarsal plate and extends from the zygomatic bone of the lateral wall to the lacrimal bone of the medial wall to provide support for the globe.
Lateral rectus specs
‣ originates from the common tendinous ring
‣ 6.9mm from the limbus
Medial rectus specs
‣ Originates from the common tendinous ring
‣ 5.5mm from the limbus
Where do recti muscles originate
CTR
Superior oblique specs
‣ Originates on the lesser wing of the sphenoid bone and the CTR
‣ Travels anteriorly before looping through the trochlea to insert on the superior lateral globe behind the equator
‣ Trochlea is considered the physiologic origin of the SO because it changes its direction of action
Spiral of Tillaux
The recti muscle insertions on the globe form the spiral of Tillaux, with the SR inserting furthest away from the MR inserting closest to the limbus
Inferior oblique specs
‣ Originates ANTERIORLY at the maxillary bone. It inserts on the inferior lateral globe behind the equator
EOMs and tenons
‣ All EOM tendons pierce tenon’s capsule, which sends a “sleeve” of CT with the tendons for a short distance before they merge with the sclera.
LR actions
Abduction
No secondary or tertiary
MR actions
Adduction
No secondary or tertiary
SR actions
Elevation
Intorsion
Adduction
IR actions
Depression
Extrusion
Adduction
SO actions
Intorsion
Depression
Abduction
IO actions
Extorsion
Elevation
Abduction
Primary action of obliques
Torsion
EOM blood supply
two muscular branches from the ophthalmic artery
◦ Superior lateral branch supplies the SR, LR, and SO
◦ Inferior medial branch supplies the IR, MR, and IO
◦ The lacrimal, supraorbital, and infraorbital arteries may provide a minor blood supply to the EOMs
EOM innervation
SR=superior CN III
IR, IO, MR=inferior CN III
LR=CN VI
SO=CN IV
Orbital fascia
◦ Composed of dense CT that covers the bones of the orbit. It provides support to the blood vessels within the orbit and serves as a point of attachment for muscles, tendons, and ligaments. It is continuous with the periosteum of the skull and bones of the face.
‣ Within the optic canal, it is continuous with the dura surrounding the brain and the ON
‣ A portion covers the lacrimal gland, the lacrimal sac, and contributes to the lining of the nasolacrimal canal
‣ The anterior orbital fascia forms the orbital septum within the upper and lower eyelids.
Sphenoid bone
single bone whose middle portion (the body) form the base of the cranium. The optic canal in each eye is located just lateral to the center of the sphenoid body
Sella Turcica
depression in the body of the sphenoid bone that houses the pituitary gland. Remember, the optic chiasm lies superior to the pituitary gland. A pituitary gland tumor can damage the nasal retinal fibers from each eye that run just superior to the pituitary gland as they cross in the optic chiasm, causing a bitemporal hemianopsia.
Lesser wing of sphenoid
projects anteriorly to connect with the frontal bone to form the roof of the orbit. “Front less”=frontal bone and lesser wing of sphenoid form the roof of the orbit.
• Things that arise from the lesser wing: levator, SO, optic nerve
• The optic canal is located within the lesser wing and contains the optic nerve and the ophthalmic artery
Greater wing of sphenoid
projects laterally to connect with the zygomatic bone to form the lateral wall of the orbit. “The great Z”=the greater wing of the sphenoid and the zygomatic to form the lateral wall of the orbit. The greater wing of the sphenoid contains 3 important foramina:
• Rotundum: V2 (rotwondum)
• Ovale: V3 (ov3ale)
• Spinosum: middle meninges artery (important in cases of truama)
Superior orbital fissure
◦ Opening between the greater and the lesser wing O.D. the sphenoid bone
‣ Located between the posterior lateral wal land the superior wall
‣ The cavernous sinus lies just posterior to the SOF and travels on the side of the sphenoid body
‣ Anterior to the SOF is the CTR
Common tendinous ring
circular band of CT that lies just anterior to the superior orbital fissure (SOF) and serves as the origin of the recti muscles. The CTR is AKA annulus of Zinn.
The following pass through the SOF and CTR
‣ Nasociliary nerve (V1), oculomotor nerve, and abducens nerve (NOA nerves)
‣ The sympathetic root of the ciliary ganglion travels with the nasociliary nerve as it passes through the SOF and CTR
The following pass through the SOF but ABOVE the CTR
‣ Superior ophthalmic vein
‣ Frontal nerve
‣ Lacrimal nerve
‣ Trochlear nerve
This passes below the SOF and inferior to the CTR
Inferior ophthalmic vein
What goes through the optic foramen
ON and ophthalmic artery
What goes through the carotid canal
ICA and sympathetic plexus
What goes through the supraorbital foramen
supraorbital nerve (V1) and vessels (supraorbital artery and vein)
What goes through the infraorbital foramen
infraorbital nerve (V2) and vessels (infraorbital artery and vein)
What goes through the mandibualr forman
inferior alveolar nerve and vessel
What goes through the stylomastoid foramen
Facial nerve
Orbital roof bones
Frontal bone
Lesser wing of sphenoid
Where does the lacrimal gland lie
the anterolateral portion of the orbital roof within a fossa of the frontal bone
Orbital floor bones
Maxillary
Palatine
Zygomatic
What part of the orbit is most prone to damage
The postero-medial portion of the floor
What is a random finding with orbital floor fractures
• The infraorbital nerve runs along the infraorbital groove of the floor before exiting the orbit through the infraorbital foramen.
◦ Loss of sensation in cheek if damaged
Which orbital wall is the thinnest
Ethmoid
Medial wall bones of orbit
SMEL Body of sphenoid Maxillary Ethmoid Lacrimal
Thinnest and smallest
Orbital portion of the ethmoid bone
also known as the lamina papyracea. An infection in the sinus cavity can often spread to the orbit through the very thin lamina papyracea, resulting in orbital cellulitis.
Lateral wall of orbit bones
Greater wing of sphenoid
Zygomatic
The great Z
What is the strongest wall in the orbit
Roof wall
Important branches of the ECA to the eye
Facial
Maxillary
Superficial temporal
Facial artery
- Branches at the angle of the mandible and travels across the mandible and cheek toward the medial canthus of the eye
* The angular artery: terminal branch of the facial artery that communicates with the dorsal nasal artery and supplies the medial canthus
Maxillary artery
- Terminal branch of the ECA that begins just anterior to the ear in the parotid gland
* The infraorbital branch of the maxillary artery enters the orbit through the inferior orbital fissure and supplies the IR and IO.
* It exits the orbit through the infraorbital foramen and supplies the lower eye lid and the lacrimal sac before joining the angular artery and the dorsal nasal artery
Superficial temporal artery
• The second terminal branch of the ECA that arises within the parotid gland
◦ It has 3 branches that supply the superficial skin, muscles, and soft tissue around the face and orbit
◦ The superficial temporal artery communicates with branches from the ophthalmic artery
GCA
inflammation of large and medium sized vessels that supply the head. Damage to the PCA (circle of zinn) leads to suffocation and irreversible damage of the ONH (AAION) and results in significant loss of vision. This inflammatory process can quickly spread to the fellow eye if not promptly treated with oral corticosteroids and is thus considered an ocular emergency.
Branches if ICA
OPAM Ophthalmic Posterior communicating Anterior cerebral Medial cerebral
anastomoses of ICA and ECA branches
‣ Branches from the ICA and ECA anastomose to provide for certain ocular structures. For example, the superficial temporal artery has a connection with the supraorbital artery; if the ophthalmic artery is obstructed and cannot provide blood flow to the orbit, this connection can temporarily provide a low level of circulation
Course of the ICA
◦ ICA enters the skull through the patrols portion of the temporal bone and travels directly into the cavernous sinus
◦ CN VI travels alongside the ICA as it course through the cavernous sinus. CN III is lateral and CN II is medial to the ICA just before it exits the sinus.
◦ The ophthalmic artery is the first branch of the ICA as it approaches the orbit
How does the ophthalmic artery enter the orbit
Within the optic nerve sheath
• After leaving the sheath, the ophthalmic artery travels near the medial wall of the orbit (along with the nasociliary nerve) between the SO and MR
Branches of the ophthalmic artery
CL MS LSE CRA Lacrimal artery Muscular artery Short posterior ciliary arteries Long posterior ciliary arteries Supraorbital artery Ethmoid artery
CRA
‣ First branch of the opthalmic artery. It travels within the optic nerve and supplies the nerve and surrounding pia mater via collateral branches. it enters the optic disc slightly nasal to center and divides into multiple superior and inferior branches. The CRA supplies the inner 2/3 of the retina
Lacrimal artery
Ophthalmic branch
‣ Travels along the lateral wall of the orbit and supplies the LR and the lacrimal gland. It terminates as branches of the lateral palpebral artery that supplies the lateral inferior and superior lids
• The lateral palpebral arteries anastomose with the medial palpebral arteries to form the palpebral arcades of the eyelids
Muscular artery
Branch of ophthalmic
‣ Provides blood to EOMs via two branches
• Superior lateral muscular artery: LR, SR, SO
• Inferior medial muscular artery: MR, IR, and IO
What forms the ACAs
• Branches of the muscular artery that supply the four recti muscles collectively from the anterior ciliary arteries, a vascular network that combines with the long posterior ciliary arteries to form the major arterial circle of the iris
Short posterior ciliary arteries
Branch of ophthalmic
‣ One or two large branches enter the eye one both sides of the optic nerve before quickly branching 10-20 times within the choroidal stroma to form the arterial network (the circle of Zinn) that supplies the superficial optic nerve head. The SPCAs also supply the posterior choroid, including the macula
What provides blood to the optic disc
Circle of zinn
SPCAs
Long posterior ciliary arteries
Branch of ophthalmic
‣ Two arteries enter the eye one each side of the optic nerve and travel between the sclera and the choroid. They join the SPCAs to form a network of blood supply to the choroid
• LPCAs provide for the anterior choroid before traveling to the CB to join with the anterior ciliary arteries to form the major arterial circle of the iris
• Overall, the LPCAs supply the iris, CB, and anteiror region of the choroid
Where is MACI
In the CB
It contains fenestrated capillaries that allow plasma to leak out, which ultimately contributes to aqueous humor formation.
Supraorbital artery
Branch of ophthalmic
SR, SO, Levator, scalp and forehead
Ethmoid artery
Ophthalmic branch
sphenoid, frontal, and ethmoid sinuses
What layer of the retina receives blood supply from both the SPCA/LPCAs and the CRA
OPL
What layers of the retina do the CRA supply
OPL
INL
NFL
Supratrochelar arety
Terminal branch of the ophthalmic artery
skin of forehead and scalp, as well as muscles of forehead
Dorsal nasal artery
Terminal branch of ophthalmic artery
supplies the lacrimal sac and then travels along the side of the nose to join the angular artery (front he facial branch of the ECA)
‣ The dorsal nasal artery branches into the medial palpebral arteries that supply the medial superior and inferior eyelids. Remember, these arteries join with the lateral palpebral arteries to form the palpebral arcades
OIS is a result of an occlusion of the
ICA or the ophthalmic artery
What’s special about the veins in the head
They do not contain valves
Venous drainage of the orbit and corresponding arteries
DOES NOT correspond to the arterial supply
Central retinal vein
drains blood from the inner 6 layers of the retina tha tare supplied by the CRA. It exits the eye through the optic nerve and then enters the cavernous sinus, either directly or after joining the superior ophthalmic vein.
Anteiror ciliary veins
◦ Drain blood from the anteiror structures of the eye including outer portion of the CB, the conjunctiva, and schlemm’s canal. The anterior ciliary veins follow the path of the anterior ciliary arteries across the tendons of the four recti muscles. They drain into the superior and inferior ophthalmic veins
Vortex veins
◦ Drain blood from the choroid. Usually one per quadrant. Drains into the superior and inferior ophthalmic veins
Superior ophthalmic vein
◦ Largest vein in the orbit. Responsible for the majority of venous drainage of the eye, receiving blood from the CRV, the superior vortex veins, the muscular veins draining the SR and MR (also receives blood from the anterior ciliary arteries), and the lacrimal vein
◦ Exits the orbit through the SOF and drains into the cavernous sinus
Inferior ophthalmic vein
◦ Originates from a diffuse network of veins along the anterior medial orbital floor between the globe and the IR. It receives blood from the muscular veins draining the MR, IR, IO, and LR (which also receives blood from the anterior ciliary veins), the inferior vortex veins, and small veins draining the inferior conjunctiva, lower eyelid and the lacrimal sac. Two branches:
‣ Inferior branch exits the orbit through the inferior orbital fissure and drains into the pterygoid plexus to communicate with the facial veins
‣ Superior branch exits the orbit through the superior fissure and drains the cavernous sinus, either directly or after joining with the superior ophthalmic vein
Supraorbital vein
originates on the forehead and joins the frontal vein near the medial angle of the orbit to form the angular vein. It sends a branch through the supraorbital notch that helps form the SOV
◦ Frontal veins: originates from a venous plexus on the forehead. It communicates with the superficial temporal vein before joining the supraorbital vein at the medial angle of the orbit, forming the angular vein
Angular vein
‣ Originates on the side of the nose and the medial angle of the orbit. It sends a nasofrontal branch into the orbit, which joins the supraorbital branch to form the SOV. The angular vein eventually beceoms the anterior facial veins at the lower margin of the orbit
• The anterior facial vein receives blood from a branch of the pterygoid venous plexus, as well as the superior and inferior palpebral veins
• It travels from the side of the nose along the masseter until it joins with the posterior facial vein, forming the common facial vein. The common facial vein drains into the internal jugular vein
Infraorbital vein
‣ Arises from several superficial veins that drain the face. It enters the orbit via the infraorbital foramen and travels along the floor of the orbit within the infraorbital groove and canal. The infraorbital vein receives branches from small veins that drain structures of the inferior orbit before emptying into the pterygoid plexus
Ptertyoid venous plexus
located with in the infratemporal fossa. It communicates with the anterior facial vein and the cavernous sinus via orbital veins and emissary veins of the cranium. The venous plexus eventually forms the maxillary vein
Superficial temporal vein
‣ Originates from the venous plexus on the side of the skull. The frontal branches and parietal branches of the venous plexus join to form the trunk of the superficial temporal vein. It communicates with the frontal, supraorbital, posterior auricular, middle temporal, and occipital veins before joining the maxillary vein within the parotid gland to form the posterior facial vein
• The middle temporal vein receives blood from the orbital vein that originates from lateral palpebral venous branches
Posterior facial vein
‣ Aka restromandibular vein; formed by the union of the superficial temporal vein and the maxillary vein within the parotid gland. Divides into anterior and posterior branches
• Anterior: unites with the anterior facial vein to form the common facial vein. The common facial vein drains into the internal jugular vein
• Posterior: joins with the posterior auricular vein (which communicates with the occipital and superficial temporal veins) to form the external jugular vein)
Occipital vein
originates at the posterior vertex of the skull. It may drain directly into the internal jugular vein or join the posterior auricular vein to drain into the external jugular vein
External jugular vein
union of the retromandibualr vein and the posterior auricular vein and drains blood from the superficial face
Internal jugular vein
continuation of the sigmoid sinus and drains blood from the common facial, occipital, lingual, and superior and medial thyroid veins.
• venous channels located in the dura mater of the brain. They are lined with an endothelium that is continuous with the endothelium of the veins and they do NOT contain valves. They are responsible for draining blood from the head back to the heart.
Dural sinuses of the head
Canvernous sinus
located between the sphenoid and temporal bones, the cavernous sinus begins just posterior to the inferior medial region of the SOF of each orbit and extends to the petrous portion of the temporal bone. The sphenoid sinus is inferior and the optic chiasm is superior to the cavernous sinus
Cavernous sinus receives blood from
superior and inferior ophthalmic veins as well as the superficial middle cerebral vein and inferior cerebral veins
Where does the cavernous sinus drain
into the superior and inferior pterosaurs sinuses, which ultimately drain into the internal jugular vein to carry blood to the heart.
may also communicate with the pterygoid plexus thorough a network of emissary vein that exit the skull through the foramen ovale and foramen lacerum
Triangle of death
‣ The area of the face from the corners of the mouth to the bridge of the nose is sometimes called the “triangle of death.” Infections in this area can gain access to the brain through the cavernous sinus because of venous communication between the facial vein and the ophthalmic veins.
Contents in the cavernous sinus
3,4,6 V1, V2
ICA
Postganglionic symp and preganglionic parasympathetic fibers
What remains intact when there is a lesion in the cavernous sinus
• Note that V3 (mandibular branch of the trigeminal nerve), CN VII, and preganglionic parasympathetic fibers that travel with CN VII (lacrimation) do not travel within the cavernous sinus. Facial muscles control (including eyelid closure) and lacrimation will therefore remain intact in patients with cavernous sinus disease.
What is CN VI close to
ICA
most likely to be affected by an ICA aneurysm
Tolosa hunt syndrome
inflammation of the SOF and/or cavernous sinus that often affects CN 3,4,5,6, resulting in painful external ophthlamoplegia and diplopia
Carotid cavernous fistula
occurs because of an abnormal communication between the arterial and venous blood supplies within the cavernous sinus. It is assocaited with a painful red eye, orbital bruit, and pulsatile proptosis
Superior petrosal sinus
◦ Drains blood from the inferior cerebral veins and some cerebellar veins. It communicates with the cavernous sinus and the transverse sinus
Inferior petrosal sinus
◦ Originates from the posterior inferior portion of the cavernous sinus. It receives blood from the internal auditory veins as well as veins from the brainstem and cerebellum. The inferior petrosal sinus exits the skull through the jugular foramen and drains into the internal jugular vein
Superior sagittal sinus
◦ Located within the superior flax cerebri (strong folds of dura mater that separate the right and left hemispheres of the brain) on the upper petrous portion of the temporal bone. The superior sagittal sinus drains blood from the superior cerebral veins. It travels posteriorly to the internal occipital protuberance, where it drains into the right transverse sinus
Inferior sagittal sinus
◦ Travels within the inferior portion of the fall cerebri between the occipital bone and the petrous portion of the temporal bone. It receives blood from the inferior cerebral veins. The inferior sagittal sinus travels posteriorly to join the great cerebral vein to form the straight sinus.
Straight sinus
◦ Originates at the junction of the fall cerebri and the tentorium. It drains blood from the superior cerebellar veins before draining into the left transverse sinus
Occipital sinus
Originates at the margin of the foramen magnum and travels within the fall cerebri along the occipital bone, it receives blood from the vertebral veins before draining the left transverse vein
Transverse sinus
◦ Travel on the surface of the tentorium along the occipital bone and the petrous portion of the temporal bone. It receives blood from the superior petrosal sinus, inferior cerebral veins, and inferior cerebellar veins. They eventually travel inferiorly to form the sigmoid sinuses
‣ Sigmoid sinus receives the inferior petrosal sinus (which communicates with the cavernous sinus). It exits the skull through the jugular foramen and becomes the internal jugular vein
Confluence of sinuses
meeting point for the superior sagittal, straight, occipital, and transverse sinuses and is located on the internal occipital protuberance of the occipital bone.
Corneas roles
• transmits and refracts light and serves a barrier against pathogen and edema
Where is there the largest refractive difference in the eye and this serves as the main refracting element?
• the air/tear film interface has the largest refractive index difference between two layers and thus serves as the main refracting element, contributing to 44D of the refractive power of the cornea.
◦ Air n=1.00, tear film n=1.336, cornea n=1.376
◦ The tear film/cornea interface contributes 5D and the cornea/aqueous humor interface contributes -6.00D to the total refractive power of the cornea
WTR
Steeper in the vertical meridian
ATR
Steeper in the horizontal meridian
Astigmatism with age
‣ Astigmatism shifts towards ATR as the crystalline lens ages. A loss of lid tension may also contribute in flattening of the vertical meridian of the cornea, contributing to the increase in ATR astigmatism
Corneal epithelium
◦ Stratified squamous non keratinized epithelium. Contains 5-6 cell layers that are approximately 52um thick. There are four difference layers of the epithelium
Hemidesmosomes
Connect BM to things
Surface layer of the corneal epithelium
composed of 2 layers of non keratinized squamous cells. The plasma membrane of these cells secretes a glycocalyx and contains microvilli and microplicae to increase the surface area and enhance the stability of the tear film.
‣ Zonula occludens and desmosomes form a tight barrier between cells to impede the intercellular movements of particles. This is the ONLY CELL LAYER WITHIN THE CORNEA THAT CONTAINS ZONULA OCCLUDENS
What is the only cell layer in the cornea that contains zonula occludens
Surface layer of the epithelium
Wing cells of corneal epithelium
2-3 cell layers joined by desmosomes to each other and to surrounding layers
Basal layer of the corneal epithelium
the ONLY MITOTIC LAYER in the corneal epithelium; composed of 1 layer of columnar cells. The basal layer of the epithelium secretes its own basement membrane (the basal lamina). The BM attaches to the underlying bowmans layer via hemidesmosomes that penetrate bowmans and attach to the extracellular matrix of the corneal stroma.
‣ Reduplication of the BM occurs with age. By 60, the BM in normal eyes doubles in thickness.
What is the only mitotic layer of the corneal epithelium
Basal
BM throughout the body consist of
Basal lamina (secreted by epithelial cells) Reticular lamina (secreted by underlying stromal cells)
3 factors that increase the risk od RCE
Poor hemidesmosome formation (trauma)
Epithelial BM dystrophies
Age related thickening of the BM
Stem cells of the corneal epithelium
originate from the palisades of Vogt, a 0.5-1.0mm band around the limbus at the same level as the basal layer, allowing for an easy transition as stem cells migrate circumferentially to become basal cells. Remember, stem cells become basal cells, and basal cells produce wing wells that migrate anteriorly to eventually become the surface layer of the epithelium
Limbal stem cell deficiency
has been shown to contribute to poor corneal epithelial maintenance in individuals with aniridia. SJS, and alkali corneal burns.
Bowmans layer
◦ An acellular layer primarily composed of random type 1 and 5 collagen fibrils . It is a transition layer from the epithelium into the stroma; it is not a basement membrane
‣ Most say Bowman’s is produced prenatal by anterior stromal fibroblasts, although there are other sources that’s say it is produced prenatally by corneal epithelial cells. It is 8-14 microns thick
‣ Tough layer that is resistant to damage or injury; however, if damage occurs, bowmans cannot regenerate, resulting in the formation of a scar.
‣ Bowmans may play a role in maintaining the correct curvature of the cornea
Conditions related to bowmans layer
- Band keratopathy: calcium deposits (Swiss cheese pattern) within bowmans
- Pterygia: Detroit bowmans layers as they progress onto the cornea
- Crocodile shagreen: bilateral gray white polygonal stromal opacities that may involve bowmans layer
- Reid-buckler dystrophy: rare corneal epithelial dystrophy that appears as early in life and is secondary to damage to bowmans layer
- Keratoconnus: inital damage occurs in bowmans layer. Remember that advanced keratoconnus may result in hydrops due to damage to descemets membrane
- Refractive surgery: the flap created during LASIK consists of epithelium AND bowmans layer; PRK involves the application of laser THROUGH bowmans layer, resulting in post op corneal haze.
Type I collagen damage diseases
OI
Ehlers danlos
Stroma of the corneal epithelium
450um thick. Dense, irregular CT composed of keratocytes (fibroblasts), collagen fibrils, ground substance, and water (75-80% of the stroma)
Keratocyes
Stroma of the corneal stroma
fibroblasts of the cornea that produce collage fibrils and the extracellular matrix
Collagen fibrils in the cornea
In the stroma
the stroma contains about 200-300 layers of uniformly spaced 30nm lamellae (comprised mainly of type I collagen) that run parallel to the corneal curface. Uniform spacing of collagen lamellae is essential for maintaining corneal transparency
Anterior vs posterior corneal stroma
- The anteiror 1/3 of the stroma has a higher incidence of cross linking between collagen fibers compared to the posterior 2/3 of the stroma, creating more rigidity and helping to maintain corneal curvature
* The posterior 2/3 of the stroma is more organized and consists very uniformly spaced lamellae that are larger and have less branches and less cross linking compared to the anterior 1/3 of the stroma, factors that result in a higher incidence of corneal edema in the posterior cornea.
Ground substance of the corneal stroma
serve as a filler between the collagen fibrils and keratocytes. Contains GAGs that attract water, contributing to the precise spacing between collagen lamellae that is essential for corneal transparency.
• Keratin sulfate: predominate GAG within the cornea
What is the predominate GAG in the cornea
Keratin Sulfate
Corneal blood supply
Avascular Obtains nutrients though -diffusion from aqueous humor -limbal conjunctiva and episcleral cap networks -palpebral conjunctival networks
Open eye: cornea gets nutrients from
Tear film
Closed eye: cornea gets nutrients from
Palpebral conjunctiva
Corneal neo
defense response to oxygen deprivation. The new vessels arise from endothelial cells of the limbal capillary network in response to stroking s and growth factors (including VEGF)
Which layer of the corneal regenerateS
Epithelium
Descemets
Only corneal layers to thicken throughout life
DM
Descemets
Corneal layer that thins with age
Endortheloiyum
Corneal innervation
• responsible for pain sensation and for proper wound healing. V1 divides into the nasociliary nerve, which then divides into the long and short posterior ciliary nerves that directly innervate the cornea.
LPCNs and corneal innervation
branch directly from the nasociliary nerve. SPCNs are formed after the nasociliary nerve travels through the ciliary ganglion. The LOCNs and SPCNs form a myelinated network of 60-80 nerves that enter the mid stroma.
◦ After traveling 2-4mm inside the stroma, the corneal nerves lose their myelin sheath as they penetrate through bowmans layer to enter the epithelium. These nerves are nor highly snesitive naked nerves packed with nocirecptors that mediate pain.
Neurotrophic keratitis
characterized by poor corneal sensitivity and wound healing and is secondary to damage to V1 of the trigeminal nerve (herpes zoster, herpes simplex, CVA, DM)
‣ V1 tells stem cells to becom basal
• Cells shed, stimulate new growth
• Detect pain
• No more signaling to produce more cells and loss of sensation. “Big ulcer, no pain”
Corneal nerve networks ultimately form in three places
◦ Epithelium: referred to as he intraepithelial plexus
◦ Anteiror stroma/Bowmans layer: referred to as the subepithelial plexus
◦ Mid stroma: stromal plexus
Where are there no corneal nerves
posterior stroma, Descemets membrane, or corneal endothelium. Remember, the corneal nerves enter at the level of mid stroma and travel anterior to form there.
Main functions of the conjunctiva
◦ Protection of the soft tissues of the eyelid and orbit
◦ Allows extensive movement of the eye without damaging soft tissues
◦ Serves as a source of antimicrobial and other immunological agents
◦ Produces the mucin layer of the tears
Two layers of the conjunctiva
Stratified non keratinized epithelial layer
Submucosa layer
Stratified non keratinzed epithelial layer of the conjunctiva
composed of cuboidal/columnar cells in the palpebral conjunctiva that become squamous cells in the bulbar conjunctiva. The superficial cells contain melanin granules, microvilli, and goblet cells.
Submucosa layer of the conjunctiva
loose CT layer that is separated into two layers
‣ Outer lymphoid layer: contains IgA, macrophages, mast cells, lymphocytes, PMN leukocytes, eosinophils, and langerhans cells
‣ Deep fibrous layer: contains collagen fibrils, fibroblasts, blood vessels, lymphatic vessels, nerves, and accessory lacrimal glands. In general, this layer is loosely attaches to underlying structures
Palpebral conjunctiva
◦ Covers the eyelid marking, tarsal plate, and the fornices
Marginal conjunctiva (palpebral conjunctiva)
lines the eyelid margins and is composed of stratified columnar epithelial cells that become continuous with the epithelium of the skin at the mucocutaneous junction of the lid. The underlying submucosa is very thin with only a deep fibrous layer
Tarsal palpebral conjunctiva
lines the tarsal plates and is composed of stratified columnar epithelium. The submucosa is thicker and contains the outer lymphoid and deep fibrous layers, which contains the accessory lacrimal glands and is strongly attached to the tarsal plate.
Fornices last palpebral conjunctiva
lines the fornices. The deep fibrous layer contains the accessory lacrimal gland and mullers muscle (in the upper fornix). The EOM fascia attach to the forniceal conjunctiva, moveing the conjunctiva in conjunction with the eye to avoid compression of blood vessles and nerves within the submucosa.
Bulbar conjunctiva
◦ Thin, translucent membrane that covers the sclera. Composed of stratified squamous cells that become continuous with the corneal epithelium at the limbus. The submucosa is loosely attached to underlying tenons capsule until appx 3mm from the cornea when it fuses with the end of tenon capsule, episclera, and sclera.
Where are goblet cells concentrated in the conjunctiva
Caruncle
Inferior nasal fornices
Temporal bulbar conjunctiva
Corneal limbus
1-2mm zone that encircles the cornea and serves as the junction between the conjunctiva, sclera, and cornea
‣ The limbus provides nutrients for neighboring structures
‣ The limbus provides a passageway for aqueous humor drainage within the eye
‣ Supplied by blood from capillary loops of the conjunctival and epi scleral vessels
Histological and anatomical changes at the limbus
‣ The limbal epithelium contains 10 cell layers compared to the 5 cell layers of the corneal epithelium
‣ Bowmans layer and descemets membrane end at the limbus. Remember that descemets membrane beceoms schwalbes line in the anterior chamber angle
‣ The conjunctival stroma, episclera, and tenon’s capsule begin at the limbus
Palisades of Vogt
spoke like projections of limbal conjunctiva that extend 4mm from the edge of the cornea. The limbal epithelium is the source of stem cells that migrate to the basal layer of the cornea
ACA injection
Scleritis/adenovirus=diffuse injection
Uveitits-circumlimbal
Plica semilunaris
composed of stratified squamous bulbar conjunctiva that folds at the medial canthus, providing slack in the conjunctiva during lateral eye movements. It also serves as the floor of the lacrimal lake
Caruncle
a hybrid of conjunctiva and skin that contains sebaceous glands, sweat glands, and goblet cells and is located on the medial side of the plica semilunaris. Function unknown. Likely the source for the collection of debris that is present in the healthy eye upon wakening
Palpebral conjunctiva blood supply
marginal and peripheral palpebral arcades.
Posterior bulbar conjunctiva
peripheral palpebral arcades. Anterior bulbar conjunctiva is supplied by the anterior ciliary arteries. The peripheral palpebral arcades combine with the anterior ciliary arteries at the posterior bulbar conjunctiva
Palpebral and bulbar conjunctiva are drained by
The antieror ciliary veins
Conjunctival lymphatics
• lateral lymphatic vessels of the bulbar and palpebral conjunctiva drain into the parotid lymph nodes. Medial lymphatic vessels drain into the submandibular lymph nodes
Conjunctival sensory innervation
innervated by the long posterior ciliary nerves (from the nasociliary nerve of V1). The superior palpebral conjunctiva is innervated by the frontal and lacrimal nerves of V1; the inferior palpebral conjunctiva is innervated by the lacrimal nerve of V1 and the infraorbital nerve of V2.
• avascular, transparent, biconvex structure located within the posterior chamber between the vitreous and the iris. Its main function is to assist in the transmission and focusing of light onto the retina
Lens
Refractive power of the lens
20D (1/3 of the total)
The posterior lens surface and the anterior vitreous face
posterior lens surface is attached to the anterior vitreous face by the ring shaped hyaloid capsular ligament. The potential space between the posterior pole of the lens and the anterior vitreous within this ring is known as the retrolental space of Berger.
What helps reduce SA in the lens
peripheral flattening and a gradient index of refraction in the lens helps to reduce spherical aberration
Lens capsule
transparent basement membrane that surrounds the entire lens and is secreted by the anterior lens epithelium. It is thinnest at the posterior pole and thickest at the anterior pole of the lens (and is thickest BM in the entire body). It is primarily composed of type 4 collagen fibers and GAGs
‣ The lens capsule serves as a barrier against large molecules entering the lens
‣ The lens zonules, which maintain the position of the lens within the posterior chamber, extend from the non pigmented ciliary epithelium and insert into the anterior capsule of the lens
Lens epithelium
composed of a single layer of cuboidal epithelial cells adjacent to the anterior lens capsule. There is NO posterior lens epithelium in the adult lens, as it was used to form the primary lens fibers during embrological development. Lens epithelial cells are joined with maculae occludens and gap junctions. They serves as the main site of lens metabolism
‣ The pre-equatorial region of the lens (just anterior to the lens equator and known as the germinal zone) containes mitotic epithelial cells that become secondary lens fibers. The production of new lens fibers is continuous throughout life.
Lens cortex
composed of 65-70% water
‣ 80-90% of lens proteins are water soluble alpha, beta, and gamma crystallins that are tightly packed within the cytoplasm of lens fiber cells.
UV exposure and oxidation to the lens
• UV exposure and oxidation can cause structural damage to lens fibers. Alpha crystallins act as molecular chaperones by helping beta and gamma crystallins recover from injuries, thus preventing degradation of lens fibers and loss of lens transparency
Alpha crystalline
Molecular chaperones by helping beta and gamma crystallins recover from injuries
Crystalline concentration in the lens
varies throughout the lens, creating a gradient index of refraction that is higher in the nucleus (n=1.41) compared to the anterior lens. Remember that aqueous and vitreous humors have an index of refraction of 1.336
Lens zonules are produced by
by BM of the NPCE in the pars plana and pars plica RA
Composition of zonules
microfibrils that contain fibrillin and extracellular matrix but NO true elastic fibers
Parimary lens zonules
directly to the lens capsule in the pre and post equatorial regions of the lens. Relatively few primary lens zonules attach directly to the lens equator.
Secondary lens zonules
connect primary lens zonules to one another or to the NPCE of the pars plana
Tension zonules
connect the primary lens zonules to the valleys between the ciliary processes of the pars plicata
Order of the layers of the lens
Adult Juvenile Fetal (Y sutures) Embryonic Fetal (Y) Juvenile Adult
What is the only type of lens fibers that arise from posterior cells of the lens
Embryonic
ALL others are from anterior
General characteristics of the scale
- forms the posterior 5/6 of the protective CT coat of the eye and helps to maintain the shape of the globe
- Point of attachment for the EOMs
- Mean radius of curvature=11.5mm
- Thickest area is 1.0mm at the posterior pole
- Thinnest area is 0.3mm under the recti tendon insertions. This is clinically relevant during strab surgery
- Weakest area=lamina cribrosa
- Considered avascular
- Minimally innervated: LPCNs and SPCNs
Episclera
loose CT that contains capillary network (from the anterior ciliary arteries) that surrounds the cornea. Inflammation of the CB or iris (iritis) will cause dilation of the anterior ciliary arteries. Leading to the characteristics ciliary flush (circumlimbal injection)
Where do the ACAs form networks
In the anterior conjunctiva and the episclera
Sclera proper
thick, dense, avasular VT that is continuous with the corneal stroma. Composed of irregular collagen bundles that provide strength but NO transparency. Contains similar ground substance to corneal stroma
Difference between the episclera and the sclera
‣ The episclera is composed of LOOSE CT and is HIGHLY vascular. The sclera proper is composed of DENSE CT and is relatively AVASCULAR
Lamina fusca of the sclera
the innermost layer of the sclera adjacent to the choroid that contains elastin fibers and numerous melanocytes
Infant scleras
the sclera commonly has a blue tint because the underlying uveal pigmentation is visible through the thinner sclera. Osteogenesis imperfecta or Ehlers-Danlos syndrome are also assocaited with a blue sclera
Elderly scleras
often becomes yellow as lipids become trapped in the dense irregular CT over time. A yellow scleral may signify liver disease
Tenons capsule
thin transparent layer of CT that covers the episclera. It begins 2mm posterior to the limbus and extends posteriorly to encircle the rest of the globe, separating it from the surrounding orbital adipose tissue
◦ Tenons capsule fuses wtih the episclera and th conjunctival submucosa layer
◦ It is perforated posterolaterally by the optic nerve, ciliary vessels and nerves, and the tendons of the 4 recti muscles
Layers of the sclera from anterior to posterior
conjunctival epithelium, conjunctival stroma, tenons capsule, episclera, sclera proper, and lamina fusca
Anterior scleral foramen
area occupied by the cornea (11.7mm in diameter)
Posterior scleral foramen
area wher ethe optic nerve enters the eye. The optic nerve is supported by the lamina cribrosa, which is composed of scleral collagen and elastin fibers that associated with the axon bundles and astrocytes within the optic nerve
Anterior emissaria of the sclera
‣ The deep and intrasceral venous plexi travel through the sclera to connect with the ciliary vein within the CB
‣ Anteiror ciliary arteries provide blood to most anterior structures of the eyes
‣ Branches from the episcleral arteries travel through the sclera to reach the anterior chamber angle
‣ Aqueous veins of Ascher drain aqueous humor drain from schlemms canal
‣ LCPNs (forming axenfeld nerve loops) provide innervation to most anterior structures of the eye
Middle emissaria of the sclera
include vortex veins that drain the choroid
Posterior emissaria of the sclera
near the optic nerve, include channels for the LPCAs, SPCAs, LPCNs, and SPCNs that travel through the sclera to reach the suprachoroidal space
Depth of AC
3.6mm
Diameter of the AC
11-12mm
Volume of AC
120-170uL of fluid
Average IOP
15.5
Boundaries of the AC
corneal endothelium, the TM, schlemms canal, ciliary body, and iris root, and the anteiror iris surface
Internal scleral sulcus
located within the eye at the corneal scleral junction and contains the site for aqueous filtration. The structures within the internal scleral sulcus, form posterior to anterior, include:
◦ Iris, CB, scleral spur, TM, Schlemms canal, and Schwalbes line
Becker-Shaffer grading system
‣ Based on the most posterior structure of the angle that is visible
• Grade 4: CB
• Grade 0: no structures available
ICSTSL
4321
Van Herick
‣ Based on width of the chamber angle compared to the width of the corneal optic section
• Grade 4: width of the chamber interval is 1/2 or greater than the width of the corneal optic section
Scleral spur
band of collagen and elastin fibers that extends from the inner aspect of the sclera. It is the origin site for the longitudinal ciliary muscle fibers and the TM lamellae
What are the only areas of the sclera that contain elastin
the scleral spur, the lamina cribrosa, and the lamina fusca are the only areas of the sclera that contain elastin
TM
◦ Lines the anterior chamber circumferentially and is the major site for aqueous humor filtration
‣ The TM is triangular in shape, with the base of the triangle abutting the scleral spur and the apex pointing towards the cornea. The juxtacanalicular tissue is the external border of the TM
‣ The inferior portion of the angle typically has the greatest amount of pigment in the TM and is therefore a good starting point when performing gonioscopy
Uveoscleral meshwork of the TM
the innermost 1-5 layers of the TM that are located adjacent to the anterior chamber and inward to the scleral spur. It consists of large pores within a network of cords, which are composed of an inner core of collagen, elastin, and ground substance surrounded by a layer of endothelium and BM. The endothelial cells aid in protein synthesis and contain lysosomes for phagocytosis of melanin and debits
• Does NOT utilize schlemms canal for outflow (PRESSURE INDEPENDENT); instead, aqueous flows between the ciliary muscle fiber bundles, into the suprachoroidal space, and then through the sclera OR drains through the anterior ciliary veins, cortex veins, or other routes.
• The uveoscleral meshwork is a minor site for aqueous humor filtration, accounting for 5-35% of total aquesou humor outflow
PGs and IOP
Prostaglandins decrease resistance in the uveoscleral meshwork by relaxing the ciliary muscle and causing changes within the extracellular matrix, resulting in an increase in uveoscleral outflow
Corneoscleral meshwork
the outer 8-15 layers of the TM that are located closer to schlemms canal and extend between the scleral spur and the cornea. It contains smaller pores with a network of sheet like fibers similar in composition to the cords of the uveoscleral meshwork. The pores are even smaller within the portion of the TM closest to Schlemms canal and within the juxtacanalicular tissue (JXT)
JXT
- The JXT is also referred to as the cribiform layer. It is the outermost portion of the TM and separates the inner wall of schlemms canal from the TM
- The JXT is composed of a layer of endothelial cells and extracellular matrix. It is through to contain few microscopic pores and therefore is the site of most resistance to aqueous outflow
- In order to penetrate the endothelial tight junctions that line schlemms canal and the endothelial cells that fill the lumen, the aqueous humor must utilize a high to low pressure gradient (IOP must be greater than the episcleral venous pressure)
Layers of the TM from inner to outer
Uveoscleral
Cornealscleral
JXT
Aqueous humor outflow through the corneal scleral meshwork is
Pressure idependent
Aqueous humor flow through the cornealscelra meshwork is
Pressure dependent
Drugs that increase aqueous outlflow
Pilo (corneo)
PGs (Uveo)
A2 agonist (uveo)
Schlemms canal
◦ Circular venous channel lined by endothelial cells. Serves as the major site of aqueous humor filtration. The inner border is located against the scleral spur and TM. The outer border lies against the sclera near the limbus
Inner wall of schlemms
lined by endothelial cells that are in contact with the JXT. The endothelial cells contain multiple giant vacuoles that transport aqueous humor across the JXT into schlemms canal
Outer wall of schlemms
lined with normal endothelial cells (no giant vacuoles) with a thin outer covering of CT. It also contains efferent vessels that drain aqueous humor out of the eye
Collector channels in schlemms
Schlemm’s canal often contains multiple channels formed by CT septae that increase the surgface area for aqueous filtration. These channels are known as internal collector channels
2 routes Wausau can drain from through schlemms
‣ Short efferents-deep scleral venous plexus-intrascleral venous plexus-episcleral venous plexus
‣ External collector channels -episcleral venous plexus
Episcleral venous plexus drains into
the anterior ciliary veins-muscular veins-superior/inferior ophthalmic veins-cavernous sinus-superior/inferior petrosal sinus-internal jugular vein-brachiocephalic vein-superior vena cava-right atrium of heart
Schwalbes line
◦ Collagenous CT that represents the termination of descemets membrane and thus delineates the outer limit of the cornea to the limbus
Posterior embryotoxon
represents an anteriorly displaced schwalbes line
Pupil placement
opening in the iris that is located slightly nasal and inferior to the center. The pupil diameter can range from 1-8mm, but under normal room illumination is an average 3-4mm
◦ The iris at the pupillary margin contains schwalbes contraction furrows that represent variations in the thickness of the posterior pigmented iris epithelium
Thickness of iris
thickest in the collarette region; thinnest at the iris root
Iris collarete
a circular ridge appx 1.5mm from the pupillary margin that served as the site of attachment for the fetal pupillary membrane during embryonic development. The collarette contains remnants of old fetal vessels in addition to active iris vessels. It divides the iris into pupillary and ciliary zones
Ciliary zone of the collarette
contains furrows that allow the iris tissue to bunch towards the periphery during dilation. Also contains radial streaks, which are often white in color and represent collagen traveling along the iris vessels
Pupillary zone of the collarrete
radial streaks are still present but are smaller because the iris blood vessles are smaller towards the pupillary margin
Crypts of Fuchs in iris
span the collarette into the ciliary and pupillary zones a
Anterior stromal iris leaf
located within the ciliary zone of the iris; contains the anteiror border layer and a smaller portion of the iris stroma
Posterior stromal iris leaf
located posterior to the anterior iris stromal leaf. It contains most of the iris stroma in the ciliary zone and the anterior border layer and all of the iris stroma in the pupillary zone
Aniridia
rare, bialteral condition that is characteritized by the complete or partial absence of the iris. It has a high association with glaucoma (75%) due to angle closure from PAS. Patients often have poor vision due to fovea hypoplasia with a subsequent nystagmus. Additional ocular associations include microcornea, lens subluxation, and ONH hypoplasia
Anterior border layer of the iris
◦ Extends from the pupil margin to the iris root. It contains multiple fibroblasts, melanocytes, and collagen fibrils. Provides definitive color to the iris.
Color of the iris
◦ Iris color is determined by the amount of melanin within iris melanocytes, NOT THE AMOUNT OF MELANOCYTES within the anterior border layer
Blue iris
the anterior border layer is thin and melanocytes continually on a small amount of melanin
Brown iris
the anterior border layer is thick and the melanocytes contain a very large amount of melanin
Pigmentation of the iris epithelial layers and eye color
◦ In both light and dark colored irises, the two iris epithelial layers are heavily pigmented. Th only condition characterized by a lack of pigment within the iris epithelial layers is oculocutaneous albinism
Iris crypts
collagenous columns located in the anterior border layer that serve as passageways for aqueous humor to enter the iris stroma. They give the anterior iris surface a rough appearance
Fuchs heterochromia
inflammation strips melanin, always shifts towards blue
Heterochromia
• Difference in iris color between eyes. It can be congenital or from other factors such as topical prostaglandins use or chronic inflammation (uveitis)
Iris stroma
• Vascularized, loose collagen network with fewer cells than the anterior border layer. It is continuous with the stroma of the CB. The iris stroma contains several important elements
Cells in the iris stroma
fibroblasts, melanocytes, lymphocytes, macrophages, mast cells, and clump cells
Nerves of the iris stroma
LPCNs, and SPCNs. Sensory and sympathetic fibers are carried within the LPCNs and the SPCNs. Parasympathetic fibers are carried within the SPCNs
Blood vessels of the iris stroma
caps are non-fenestrated (zonula occludens junctions) and form part of the blood aqueous barrier
MACI
located in the CB close to the iris root and extends radially through the iris stroma up to the pupillary margin. It is formed by anastomoses between the LCPAs and the anterior ciliary arteries
Minor arterial circle of the iris
located within the iris stroma near the pupillary margin and inferior to the collarette. It is formed by anastomoses of the radial arteries that branch from the major arterial circle of the iris
Veins of the iris
radial veins of the iris parallel the radial arteries. They drain blood from the iris into the CB veins-choroidal veins-vortex veins-superior/inferior ophthalmic veins
Sphincter muscle
circular smooth muscle anchored firmly in the iris stroma and to the dilator muscle. The sphincter muscle originates from the anterior iris epithelial cells that detach and migrate into the iris stroma and become smooth muscle cells. It is innervated by CN III parasympathetic fibers traveling with the SPCNs. Parasympathetic stimulation results in pupil constriction
What’s in the anterior border layer
Malenin
Eye color
What’s in the stroma of iris
Blood vessles
Minor arterial circle
Sphincter
What’s in the anterior epithelium of iris
Dilator
What’s in the post epithelium of itis
Pupillary ruff
Pigment dispersion syndrome
Anterior epithelium
• anterior iris epithelium: lies closest to the iris stroma and extends posteriorly to become the pigmented epithelium of the CB. Contains pigmented myoepithelial cells that contain muscular processes at the basal surface that extend into the iris stroma and attach to the iris sphincter muscle, forming the dilator muscle. D
Dilator muscle
extends radially from the iris root into the pupillary zone and terminates at appx the midpoint of the iris sphincter muscle. Sympathetic stimulation of the dilator muscle results in dilation of the pupillary portion of the iris and is pulled towards its origin at the itis root
Posterior pigmented iris epithelium
• heavily pigmented single layer of columnar cells attached to the pigmented anteiror iris epithelium. It extends posteriorly to become the NPCE-then the sensory retina
◦ The pupillary ruff is formed by the posterior and anteiror iris epithelial layers curling anteriorly towards the anteiror border layer of the iris
PDS and iris
pigment release from the heavily pigmented iris epithelial layers rubbing against the lens zonules, resulting in peripheral iris transilumination defects. Releases pigment may accumulate on the anterior capsule, iris surface, corneal endothelium, or TM and may result in subsequent glaucoma due to poor aqueous outflow
How are the anterior and posterior pigmented epithelial layers connected
apex to apex by desmosomes and microvilli. Iris cysts can develop there is their is a separation between the two epithelial layers
Posterior chamber
• located between the iris and the anterior vitreous and is bound by the posterior surface of the iris, the anterior face of the vitreous, the equatorial region of the lens, and the CB. It has a total volume of apex 0.060mL. Composed of three regions
Three regions of the posterior chamber
◦ Posterior chamber proper: bound by the posterior iris epithelium, the ciliary processes, and the anterior zonules and surface of the lens
◦ Canal of Hanover: aka circumlental space. Located between the anterior and posterior lens zonules over the equator of the lens. Also contains the equatorial zonules
◦ Canal of petit: aka retrolental space. Located between the most posterior lens zonules, the anterior hyaloid membrane, and the posterior portion of the CB
• triangular structure with its base located at the scleral spur, iris root, and anteiror chamber, and the apex pointing posteriorly at the ora serrata. It is bound eternally by the scleral and internally by the posterior chamber and vitreous.
ciliary body
Functions of the CB
◦ Aqueous humor production: the NPCE cells produce and secrete aqueous humor into the posterior chamber
◦ Accommodation: CN III parasympathetic fibers in the SPCNs from the cilairy ganglion innervate the CB and cause contraction and subsequent accommodation
Pars plicata
wide anterior portion that contains 70-80 ciliary processes that extend into the posterior chamber
Valleys of Kuhnt
heavily pigmented areas located between the ciliary processes
What part of the CB is the NPCE located on
Pars plicata
Aqueous humor flow
pars plicata-posterior chamber-pupil-anterior chamber-TM
Pars plana
flatter, more posterior portion that begins at the pars plicata and extends posteriorly to the ora serrata; it serves as the anterior border of the retina, located 5mm anterior to the equator
Dentate processes of the pars plana
extensions of the peripheral retina (ora serrata) onto the ciliary body (pars plana)
Oral bays of the pars plana
posterior extensions of the pars plana that lie between the dentate processes
Enclosed oral bays
• Neighboring dentate processes can join together, forming an enclosed oral bay; this can be confused with a retinal hole
Course of the lens zonules
arise within the tertiary vitreous from the BM of the NPCE in the pars plana and from the valleys between processes in the pars plicata
Lens zonules arise from the _____vitreous
Tertiary
Lens counsels produced by the pars plana
extend first to the valleys of Kuhnt of the pars plicata before inserting into the lens capsule
Ruptured or damaged lens zonules
Cause subluxation or dislocation of the lens
Supraciliaris
outermost layer. Loosely attached to the underlying sclera. It is a potential space filled with loose CT with numerous collagen bands
What is the supraciliaris continuous with at the ora
suprachoroidal (outer layer of the choroid) at the ora serrata. Blood vessels and nerves travel from the suprachoroidal through the supraciliaris to reach the anterior portion of the eye
Fluid accumulation in the potential space of the supraciliaris
ciliary body detachment
Ciliary muscle
largest intrinsic muscle of the eye. Composed of smooth muscle fibers that are responsible for accommodation. Innervated by CN III parasympathetic fibers. Anchored anteriorly to the scleral spur and posteriorly in the stroma of the choroid. Contains 3 types of fibers: longitudinal, radial, and mullers annular muscle
Longitudinal muscle of the CB
outermost fibers that comprise the largest proportion of CM fibers. Form a V shape, originating at the scleral spur and the TM, with legs extending into the choroid as stellate-shaped terminations (muscle stars)
Radial fibers of the ciliary muscle
V shaped from the scleral spur. Terminate by inserting into the CT near the base of the ciliary processes
Mullers angular muscle of the ciliary muscle
circular muscle bundles that comprise the smallest proportion of the CM fibers. The most medial ones. Located near the MACI. Originate from the scleral spur and have action similar to iris sphincter when activated
Ciliary stroma
between the CM and the epithelial layers. Highly vascularized and contains the MACI
MACI
In the ciliary stroma
located inward from the CM near the iris root. It contains large, fenestrated caps located near the ciliary epithelium of the pars plicata that are formed by anastomoses of the LPCAs and the anterior ciliary arteries
MACI and NPCE
‣ Although large substances are capable of exiting the blood from the fenestrated caps, the tight zonular junctions of the NPCE regulates the release of these molecules into the anterior chamber
‣ As an example, the protein concentration in the blood is 7% compared to only 2% in the aqueous humor
Aqueous humor production
produced from plasma that escapes the blood stream via the fenestrated caps of the MACI
Ciliary epithelium
composed of two layers of epithelium that line the ciliary body and are joined apex to apex via zonulae occludens to form part of the BAB. Both epithelial layers contain highly active cells
Pigmented ciliary epithelium
outer cuboidal epithelial layer that is attached to the ciliary stroma via the basal lamina of the BM
‣ Anterior: continuous with the pigmented anteiror iris epithelial and its BM
‣ Posterior: continues with the RPE and the inner BM portion of Bruchs membrane
NPCE
inner cuboidal/columnar epithelial layer that lines the posterior chamber. Lens zonules arise from the basal lamina at the pars plana and the valleys of the pars plicata. Also contains numerous organelles that are necessary for aqueous secretion.
Blood supply to the CB
- branches from the LCPAs and the MACI supple blood to the CB
- Veins within the CB eventually drain through the vortex veins
Innervation of the CB
- CN III parasympathetic nerve fibers travel with SPCNs from the ciliary ganglion to supply the CM for accommodation
- Sympathetic nerve fibers from the superior cervical ganglion of the sympathetic ganglion chain travel with the LPCNs and the SPCNs to innervate arteries within the CB
- Sensory nerve fibers from the trigeminal ganglion of V1 travel with LCPNs to the CB
Where are there fenestrated vessels in the eye
MACI (CB)
Choroid
Nonfenestrated vessels
minor arterial circle of iris
Retina
General characteristics of the choroid
- located between the sclera and the RPE and extends from the ora serrata to the optic nerve
- Thickest in the posterior pole and thinnest at the ora serrata
Layers of the choroid
- Suprachoroidal lamina (lamina Fusca)
- Choroidal stroma
- Choriocapilaris
- Bruch’s membrane
Suprachoroidal lamina (lamina fusca) of the choroid
potential space located between the sclera and the choroidal vessels. It is loosely packed with collagen fibers, fibroblasts, melanocytes, and extracellular matrix
◦ Serves as the passage for the LPCAs and the LPCNs that travel from the posterior to the anterior region of the eye
◦ The suprachoroidal layer contains components of BOTH the choroid and the sclera (it does not belong exclusively to the choroid). If the choroid and sclera are separated, part of the suprachoroid will adhere to the sclera and part will adhere to the choroid
Choroidal stroma
loose CT layer that contains choroidal blood vessels, nerves, and dense melanin granules
◦ The choroidal vessels are innervated by the sympathetic nervous system, which causes vasoconstriction
◦ The high density of blood vessels and melanin granules within the choroidal stroma creates the potential space for the development of choroidal melanomas
Where do the LPCNs extends from
the mid equatorial region to the ora serrata along the 3 and 9 o clock meridians
Most common primary tumors in adutls
Choroidal melanoma
Layers of the SPCA vessels within the choroid
Haller’s layer
Sattler’s layer
Hallers layer of the SPCA vessles in the choroidal stroma
posterior layer composed of large vessels that branch into smaller vessels that form Sattlers layer. The tributaries of the vortex veins are also located within Haller veins. It’s not good if you can see these. They are the large orange vessels
Sattler’s layer of SPCAs in the choroidal stroma
anterior layer composed of smaller vessels that branch for form a cap bed. The veins that drain blood from the cap bed are the large vortex veins. Unlike most veins i nthe body, vortex veins DO NOT contain valves
Choriocapilaris
composed of large bed of fenestrated capillaries that are most concentrated within the macula. Provides nourishment to the outer layers of the retina.
◦ Contains few pericytes that surround the cap walls and provide local regulation of blood flow. (Damaged in DM)
DM and the choriocapilaris
‣ DM can damage the blood vessels and pericytes of the choroid, preventing proper diffusion of nutrients and O2 to the macula and resulting in diabetic retinopathy.
Bruchs membrane
the thin (2um) innermost loafer of the choroid that extends from the optic nerve to the CB. It represents the fusion of th echoriocapillaris and the RPE BM. Bruchs membrane is composed of the following 5 layers
‣ BM of the choriocapillaris
‣ outer collagenous layer
‣ Elastic layer (very strong)
‣ Inner collagenous layer (Drusen in AMD)
‣ BM of the RPE
Bruchs and nutrients
pass from the choriocapillaris through Bruch’s membrane and into the retina
Waste and bruchs
pass from the retina through Bruchs to the choriocapillaris
Phospholipids on bruchs
accumulate on Bruchs membrane with age, causing it to become hydrophobic; this impedes water movement, thereby inhibiting the transport of metabolites.
Drusen
deposits of waste material from the retina between the inner collagenous layer of bruchs and the the BM of the RPE. They occur as a result of the decline in nutritional supply to the retina and are the characteristic finding in AMD
CNVMs
• Result from a break in bruchs membrane that can occur in a variety of conditions including exudative AMD, pathological myopia, histoplasmosis, choroidal rupture, best disease, and pseudxanthoma elasticum (angioid streaks)
Angioid streaks
◦ Angioid streaks result from damage to the elastic layer of bruchs. Remember PEPSI for Association’s with angioid streaks ‣ PXE ‣ Ehlers danlos ‣ Pagets ‣ Sickle cell ‣ Idiopathic
Disease associated with breaks in Bruch’s membrane
‣ Choroidal rupture (trauma) ‣ Histo (choroiditis) ‣ Best (lipofuscin in breaks) ‣ ADM (wet, free radicals) ‣ Lacquer cracks (high myopia) ‣ Angioid streaks (PEPSI) • All of these can cause a PED • Number one reason people go blind in US is because of a break in Bruchs
CHBALA
Blood supply to the choroid
◦ LPCAs nourish the anteiror choroid
◦ Branches of the SPCAs for mthe choriocapillaris and provide blood to postieror choroid
◦ Vortex veins drain the choroid
Innervation to the choroid
LPCNs/SPCNs carry parasympathetic, sympathetic, and sensory fibers to innervate the choroid
‣ Sympathetic fibers from the superior cervical ganglion cause vasoconstriction of the chorodial vessels
‣ CN VII parasympathetic fibers from the pterygopalatine ganglion cause vasodilation of the choroidal vessels
‣ CN III parasympathetic fibers originate from the ciliary ganglion and have an unknown function within the choroid
‣ CN V1 provides sensory innervation to the choroid
Volume of vitreous chamber
4mL; thus it makes up appx 80% of the globe and is easily the largest single structure of the eye
Shape of the vitreous chamber
spherical in shape except anteriorly, where it is concave due to the presence of the lens. This bowl shaped depression in the anterior vitreous is called the patellar fossa
Contents of the vitreous
• appx 98.5-99.7% H20 within a matrix of type II collagen and HA. Consistency is deterred by the interaction between the collagen fibrils and HA
◦ Early in life, the vitreous is almost entirely gel, by age 70-80, the vitreous is evenly composed of liquid gel and gel
◦ Most of the changes in the collagen fibril/HA complex occur within the central vitreous
Halocytes
Fibroblasts
Halocytes in the vitreous
predominate cell type. Exclusively located in the vitreous cortex. Responsible for synthesizing HA and may have phagocytic properties
What is the predominate cell type in the vitreous
Halocytes
Fibroblasts in the vitreous
predominately located int he vitreous base and likely synthesize collagen fibrils
Floaters
occur whrn the HA/collagen complex is disrupted and the collagen clumps up in bundles. Over time, liberated collagen can contract within the vitreous gel, causing posterior hyaloid membrane to detach from the retina, resulting in a posterior vitreous detahcment (PVD). A Weiss ring is formed when the posterior hyaloid completely detaches from the optic disc
Vitreal attachments (strongest to weakest)
Vitreous base (ora) Posterior lens Optic disc Macula Retinal vessels
If someone has floaters, what part of the retina do you need to be sure to check
The ora with a 3 mirror
Floater and the ONH
Weiss ring
ERM is caused by
Glial cells from back of viretous and inside the retina
Mac hole from vitreous traction/VMT
If the vitreous pulls on the retinal blood vessels
Preretinal/vitreous heme
Vitreous cortex
◦ Outer region of the vitreous adjacent to the retina that extends to the ora serrata. Consists of a high density gel filled with collagen fibrils, cells, proteins, and a mucopolysaccharide filler substance. The vitreous cortex is divided into anterior and posterior hyaloid regions by the vitreous base, an area at the ora serrata tha that the strongest attachment to the vitreous.
Anterior hyaloid
extends from the vitreous base anteriorly to attach to the lens
Patellar fossa
depression of the anterior vitreous caused by the posterior Lens
• Hyaloideocapsular ligament of Weiger
strong circular adhesions between the anterior vitreous, postieror zonules, and the posterior capsule of the lens
Berger’s space
a potential space between the anterior hyaloid and the posterior lens capsule that is located in the central area of the non-adhesion withi nthe circular hyaloideocapsular ligament
Posterior hyaloid
begins at the posterior edge of the vitreous base and extends posteriorly to the optic disc
Cloquet’s Canal
A normal remnant of the primary vitreous that is located in the center of the vitreous cavity. It is composed of a channel of low density liquid vitreous surrounded by a wall of high density gel vitreous
‣ Represents the former site of the hyaloid artery that was responsible for nourishing the avascular lens during embryological development
‣ After development, the hyaloid arter regresses to the optic disc where is becomes the CRA
‣ The posterior end of the canal near the optic disc is known as the area of martegiani.
Epicapsular star
located on the anterior lens capsule; it is the embryological remnant of the former connection between the anterior tunica vasculosa lentis and the posterior hyaloid artery
Mittendorfs dot
embryological remnant of the hyaloid artery on the posterior lens capsule
Bergmeisters Papilla
embryological remnant of the hyaloid artery on the optic disc.
The retina is derived from the
Neural ectoderm
Layers of the retina
RPE-PR-ELM-ONL-OPL-INL-IPL-GCL-NFL-ILM
RPE
• single layer of cuboidal pigmented cells. The apical side of the cells face the retina and the basal side lies adjacent to bruchs membrane. The BM of the RPE strongly adheres to the choroid, forming the innermost portion of bruchs membrane
the RPE is derived from the
Outer layer of the optic cup
Apical side of the RPE
◦ Although RPE has NO intercellular junctions with the rods and cones, the apical side of the RPE cells contains microvilli that extend into the PR layer to surround the PR outer segments. These microvilli are responsible for phagocytosis of the PR outer segments
The potential space between the RPE microvilli and the PR outer segments
is filled with interphotoreceptor matrix that has a varied chemical composition around rods compared to cones
The subretinal space between the RPE and the neural retina can lead to
lead to the deployment of retinal detachments
Functions of the RPE
- Phagocytosis of PR outer segments
- Transfer of ions, water, and metabolites
- Vitamin A storage and metabolism
- Blood retinal barrier
- Absorbs light
- Produces growth factors for tissue maintenance
RPE: phagocytosis of the PR outer segments
RPE cells are highly active and contain smooth ER, rough ER, golgi, and lysosomes. Undigested material from outer segments can accumulate within RPE cells as lipofuscin, which can contribute to RPE cell death
Lysosomes and the RPE
lysosomes are found within RPE cells and play a significant role in phagocytosis of the PR outer segment layer
RPE: transfer of ions, water, and metabolites
RPE cells transport substances between the choroid and retina through a complex process that involves multiple pumps, co-transporters, and channels. Examples include the following
‣ Proton-lactate water cotransporter moves lactate, a byproduct of anaerobic respiration from the RPE to the choroid
‣ Glucose transporter moves glucose from the choroid to the RPE to ensure a steady supply to the PR
What moves lactate from the RPE to the choroid
Proton-lactate water cotransporter
Glucose transporter in the RPE
Moves glucose from the choroid into the RPE to ensure a steady supply to the PR
Vitamin A storage and metabolism of the RPE
RPE cells play an important role in the visual cycle by recycling vitamin A (all-trans retinol) and retinoids between the PR and the RPE
RPE: blood retinal barrier
RPE cells are tightly linked together by a terminal complex that includes zonules occludens, zonulae adherents, and maculae adherents, forming the blood retinal barrier
RPE: absorbing light
RPE cells contain pigment granules that absorb stray light that is not absorbed by the rods and cones
Producing growth factors for tissue maintenance: the RPE
RPE cells produce VEGF which is essential for choroicapillaris function, as well as pigment epithelial derived factor (PEDF), an antiangiogenic factor that counterbalances the effects of VEGF
Myoid
Inner layer of the inner segment that contains ER and Golgi apparatus for protein synthesis
Myopia=makes protein
Ellipsoid
The outer layer of the inner segment that is packed with mitochondria
Ellipsoid=energy
Cillium of the PR
Connects the outer and inner segments of the PR
Outer segment of the PR
contains stacks of membranous discs that contain photopigments produced by the inner segment
‣ The outer segment produces the discs that surround the photopigment molecules. There are appx 600-1000 discs per rod and 1000-1200 per cone
‣ Disc membranes are continues with the plasma membrane in cones but are free floating (NOT continuous with the plasma membrane) in rods
Disc photopigments are formed
in the inner segment assembled into discs at the base of the outer segment, and are continually shed at the tip of the outer segment for phagocytosis by the RPE
Rods
◦ Used for scotopic vision; rods detect objects under low levels of illumination
◦ Rod density is greatest about 5mm (20 degrees) concentrically from the fovea in an area known as the rod ring
◦ Rod discs contain photopigment rhodopsin, which absorbs photons maximally at 507nm; rhodopsin DOES not detect color
◦ Rods terminate in spherules (compared to cones, which terminate in pedicles)
Cones
Used for photopic vision. Cones contain 3 different photopigments (iodopsins) that each contain the same chromophore (11-cis-retinal) but differ in their protein (opsin) component
‣ Cyanolabe (blue): max absorbs at 440nm
‣ Chlorolabe (green): 535nm
‣ Erythrolabe (red): 565
Location of the fovea relative to the ONH
The fovea is 5mm temporal and 0,4mm inferior to the center of the ONH (superior and nasal to the ONH if viewing with a 78 or 90D condensing lens) and contains ONLY cone photoreceptors at the highest concentration in the retina
ELM
• not a true membrane and does not contain any cells. It is formed by a band of desmosomal attachments between muller cells and the inner segments of the PR. Ir provides structure to the retina and acts as a barrier against large metabolites
ONL
• contains the cell bodies of the rods and cones
OPL
• location of synapse between rod spherules and cone pedicles and the dendrites of bipolar and horizontal cells
Rod spherules
each rod spherules can synapse with 1-4 rod bipolar cell dendrites (the ONLY type of bipolar cell rods synapse to). Horizontal cell dendrites may also connect to rod spherules
Cone pedicles
larger than rod spherule. Can form a synaptic triad that consists of 3 horizontal cell dendrites OR 2 horizontal cell dendrites on either side of 1 bipolar cell dendrite with an invagination in the cone pedicle.
◦ Cone pedicles may synapse with midget, flat, or diffuse flat bipolar cells
Site of the first synapse within the visual pathway
OPL
What is Henles layer in the macula
OPL
The only retinal layer to receive blood supply from the choroid AND the retina
OPL
What layers of the retina are supplied by the CRA
NFL, GCL, IPL, and INL, and a portion of the OPL.
Reintoschisis
Splitting of the OPL
Where are hard exudates located
OPL
IPL
• location of the synapse between the 2nd order (bipolar) and 3rd order (ganglion cell) neurons in the visual pathway. Amacrine cells modify the synapse between the bipolar and ganglion cells by providing temporal input and increasing signal resolution
Bipolar cells synapse with
One process from an amacrine cell and one dendrite from a ganglion cell
Amacrine cells synapse with
Bipolar cells, ganglion cells, interplexifme cells, and amacrine cells within the IPL
Excitatory cells in the retina
RP, bipolar, ganglion
Inhibitory cells of the retina
Horistonal
Amacrine
Ganglion cell layer
• the location of the ganglion cell bodies. Each ganglion cell has a single axon that travels within the optic nerve and terminates in the LGN or other areas of the brain
Where are there no ganglion cells
In the foveola
P cells
parvocellular cells have small diameter axons and are sensitive to color and fine detail. More common than M cells and project to the parvocellular layers of the LGN (3/4/5/6).
P1-cells
midget ganglion cells. Most common ganglion cells and contain only one dendrite that synapse with one midget bipolar cell, which connects with one cone PR within the fovea
P2 cells
larger, contain multiple dendrites that synapse multiple bipolar cells
M cells
magnocellular cells have larger diameter axons and are sensitive to dim changes in illumination and motion. M cells reject to the magnocellualr layers of the LGN (1 and 2)
Types of ganglion cells
M cells and P cells
Midget ganglion cells
‣ Midget ganglion cells are responsible for resolving fine detail because they carry visual info from a single cone PR within the fovea
Nerve fiber layer
• composed of axons of ganglion cells that collectively form the ON
Where is the NFL thickest
At the superior and inferior optic disc margin where the largest proportion of axons enter the optic nerve
Where is the NFL not present
In the fovea
Papillomacular bundle
consists of the NFL fibers that extend from the macula and insert on the temporal margin of the optic disc
‣ The superior and inferior temporal fibers arc over the papillomacular bundle and insert at the superior and inferior margins of the optic disc
‣ The superior and inferior nasal fibers insert directly into the superior and inferior nasal margins of the optic disc
Abnormal findings of the NFL
- CWS: soft exudates, located within the NFL an most commonly caused by DM
- Splinter hemorrhage: drance heme, hemes that occur within the NFL at or near the disc margin
- Flame hemorrhage: within the NFL and are associated with retinal vascular pathology
Dot blot hemes
assocaited with deep retinal vascular pathology and are found within the INL. CWS, splinter hemes, and flame hemes, are associated with superficial retinal vascular pathology and are found within the NFL
ILM
• the innermost boundary of the retina (closest to the vitreous) that is continuous with the inner limiting membrane of the ciliary body. The ILM is comprised of the footplates of muller cells and their basal lamina and are bound to vitreous humor collagen fibrils
◦ The ILM is present over the macula but NOT over the optic disc. Astrocytes replace the footplates of muller cells at the optic disc
◦ Epiretinal membranes occur on the ILM and are commonly located within the macula
Is the ILM present over the macula
Yes
Where is the ILM not prestn
Over ther ONHY
What replaces the footplates of the ILM at the ONH
Astrocytes
Neural messaging
‣ 128 mill PR-35 mill bipolar cells-1.5mil ganglion cells
‣ the neural message is highly refined from the PR to the ganglion cells
‣ The optic nerve acts like a bottleneck through which all visual information must pass through.
Neuroglial cells
Muller cells
Astrocytes
Microglial cells
Muller cells
the most common glia cell that is present exclusively in the retina. Extend from the ELM to the ILM. Most cell bodies located within the INL
◦ Although not found within the PR layer, microvilli from the apical surface of muller cells may extend towards the inner segments of the PR to form fiber baskets
Muller cells provide structural and nutritional support to the retina in the following ways
‣ Maintain alignemtn of other neurons within the retina
‣ Provide nutrients to the retina and aid in glycogen metabolism
‣ Act as a buffer and regulate electrolyte concentration within the extracellular space (particularly K+ concentration)
‣ Absorb and recycle metabolic waste products such as GABA and glutamate
Metabolism of the retina
◦ Retina is highly metabolic. It’s primary source of energy is glucose that is produced via anaerobic glycolysis. O2 and nutrients are transported across the RPE into the inner segments of the PR. Excess glucose is converted to glycogen and stored in muller cells to ensure the PR have a constant supply of nutrients.
Astrocytes
most concentrated within the inner retinal layers. Fibrous cells that provide structure to nerve fibers and retinal caps
◦ Astrocytes help form the ILM at the optic disc (muller cells form the ILM throughout the rest of the retina). They perform similar functions as muller cells
Microglial cells
phagocytic cells that respond to inflammation and/or injury. Microglial cells can be found anywhere in the retina.
Neurglial cells and signal processing
◦ Neuroglial cells have NO ROLE in signal processing. They provide protection and structural support to the retina.
Blood supply to the outer 5 layers of the retina
Choroida
Vortex veins
Blood supply to the inner 5 layers of the retina
CRA
CRV
What layer receives blood from CRA and choroid
OPL
CRA networks
Superficial network in the NFL
Deep cap in the INL (near the OPL)
Cilioretinal branch of the SPCA of the choriocapilaris
supplies the inner layers of the macula. It is present in 15-20% of the population and allows the macula to be spared in a CRAO
What do Retinal arteries and veins share
• Retinal arteries and veins share a common adventitious at AV crossings. Because of this close relationship, damage to the arterial walls resutls in venous wall compression and thrombus formation. This explains why almost all branch retinal vein occlusion occur at AV crossings.
How large is the macula
3.5DD
Diameter of the macula
5.5mm
How far is the macula from the ONH
3.5mm from the lateral edge and 1mm inferior
Xanthophyll pigments of the macula
zeaxanthin and lutein) that are responsible for reducing chromatic aberration and may provide protection against free radicals. Mostly found withinin the inner segments of the PR (and to a lesser extend, in the outer segments of the rods); they contribute to the more yellow appearance of the macula compared to the surrounding retina.
Fovea
1DD
1.5mm diamter
Foveal avascular zone
‣ The central 0.40-0.50mm of the fovea is avascular in order to minimize light scattering and allow for resolution of fine details. This area is supplied by the underlying choriocapillaris via the SPCAs
Foveola
0.35mm diamter
0.13mm thickness
Last area of the retina to mature during development
What is the last area of the retina to mature during development
Foveola
Thinnest area of the retina
Foveola
What cells are in the foveal
ONLY PR
The ganglion cells, bipolar cells, and other retinal cells are displaced laterally in order to minimize light scattering
Where is the retina the thickest
Parafovea
Where is the highest concentration of cone
Foveola
Area of best VA
What type of cones are missing from the foveola
S cones
Rods
Retinal layers within the foveola
RPE, PR, ELM, Henle’s fiber layer, and ILM
Henles fiber layer
term used for the OPL at the macula. This layer contains the axons of PR. There are no bipolar cells or ganglion cells withi nthe fovea or foveola (and thus not INL, IPL, GC layer, or NFL)
Parafovea
◦ 0.5mm zone that surrounds the fovea (1mm). The clivus (sloping of the retinal layers within the macula) marks the boundary between the parafovea and the fovea. ALL retinal layers are present within the parafovea
‣ The parafovea is the thickest area of the retina and contains the largest number of bipolar cells (7-11 layers) and ganglion cells (7-11)
Perifovea
◦ 1.5mm zone that surrounds the parafovea (total 3mm)
‣ Boundary between the peri and parafovea is the location where the ganglion cell layer becomes 4 cell layers thick. Boundary between the perifovea and the periphery is where ganglion cell layer is one cell thick
Where does the density of rods increase outside of the fovea
Density of rods increases at 1.2-1.7mm from the center of the fovea. Density peaks 5mm from the center of the fovea and forms the rod ring just outside perifovea
Peripheral retina terminates where
5mm anterior to the equator of the eye at the ora serrata
Ora serrata
2mm band at the anterior most portion of the retina and is composed of dentate processes and oral bays
‣ Dentate processes are extensions of peripheral retina onto pars plana of the CB
‣ Oral bays are extensions of pars plana into the peripheral retina
At the peripheral retina, what happens
◦ The RPE becomes the pigmented ciliary epithelium
◦ The neural retina significantly thins and transitions into the NPCE
◦ The vitreous base, the strongest attachment between the vitreous and the retina extends over and posterior to the ora serrata
◦ Retinal vasculature becomes very limited towards the ora seratta. The peripheral 1.5mm of anterior retina contains very few, if any, capillaries
Sensory CN
1,2,5,7,8,9,10
Motor CN
3,4,5,6,7,9,,10,11,12
Both motor and sensory CN
5, 7, 9, 10
Facial nerve function
Facial expression
Ant 2/3 tast, lacrimation, salivation
Glossopharyngeal nerve function
Swallow, salivate, post 1/3 taste
Vagus nerve functions
Taste, swallow, palate elevation, talk, viscera
Accessory nerve function
Head turn
Shoulder shrug
Hypoglossal nerve function
Tongue movement
Uvula in a CN X palsy
Uvula away from the side of the lesion and the palate does not elevate. Patient will report a hoarse voice
CN XII palsy and tongue
Tongue towards the side of the lesion
Optic nerve
◦ Sensory information only. Composed of axons of ganglion cell bodies within the GCL of the retina. All axons converge at the optic disc, exit the sclera at the lamina cribrosa, and leave the orbit via the optic foramen to travel through the optic canal
Nasal fibers of the optic nerve
from GC bodies nasal to the fovea) cross at the optic chiasm to join the temporal fibers of the other eye within the optic tract
The optic tract contains
• The optic tract contains nasal fibers from the contralateral eye and temporal fibers from the ipsilateral eye that carry info from the same side of the visual field
CN II fibers travel to one of three final destinations
- LGN: relates visual information to the primary visual cortex (V1)
- Pretectal nucleus: involved in pupil innervation
- Superior colliculus: saccades
CN III
◦ CN III has a right and left nucleus located in the midbrain at the level of the superior colliculus. Each nucleus contains sub-nuclei that proved voluntary motor control to the SR, MR, IR, and IO muscles, as well as an EW nucleus that provides parasympathetic innervation to the ciliary and iris sphincter muscles through the ciliary ganglion
CN III nuclei
‣ CN III nuclei are connected to the nuclei of CN IV, VI, and VIII through the medial longitudinal fasciculus (MLF). They also receive information from the superior colliculus and the visual cortex
CN III fibers only cross for which EOM
Superior rectus
CONTRA SR
The levator palpebrae muscel for each eye is controlled by
Only one central subnucelus of CN III
Lesion of the levator subnucleus
Will resutls in a sudden onset bilateral ptosis
How do the fibers of CN III travel
◦ Fibers fro mthe sub-nuclei join together as they exit the brainstem and then travel in close proximity ro the PCA before piercing the roof of the cavernous sinus. Within the cavernous sinus, CN III receives sympathetic fibers from the ICA plexus. CN III divides into superior and inferior divisions just before it enters the superior orbital fissure
Superior division of CN III
• Innervated the SR and superior levator palpebrae muscle. Sympathetic fibers travel with the superior division to innervate mullers muscle of the upper eyelid
Inferior division of CN III
- Innervated the MR, IO, IR, iris sphincter muscle, and ciliary muscle
* The inferior division contains parasympathetic fibers from the EW nucleus that course to the CG; these fibers leave the ganglion as SPCNs and innervate the iris sphincter and the ciliary muscle for pupillary contrition and accommodation.
Pupillary fibers of CN III
located on the outside of all other fibers within CN III. This is important to understand if a CN III lesion is an emergency or not
Cn III palsy that is pupil involving
should immediately raise suspicion for an aneurysm of the PCA. The pupil is invovled because of the aneurysm pushing on the pupillary fibers on the outside of the CN III
Where is the most likely place of a pupil involving CN III palsy
Junction between the PCA and the ICA
Pupil sparing CN III palsy
likely caused by ischemia of the small blood vessels that nourish the inner fibers of CN III, most likely as a result of DM or HTN. Since the pupil is not involved, the likelihood of a compressive lesion pushing on CN III is low
Trochlear nerve
◦ Longest and skinniest nerve
◦ Contains two nuclei that are located in the midbrain at the level of the inferior colliculus
◦ The CN IV nuclei are connected to the nuclei of CN III, VI, and VIII through the MLF. They also connect to the superior colliculus via the tectobulbar tract, which then connects to the visual cortex
◦ TCN VI is the ONLY cranial nerve that leaves the dorsal side of the midbrain and decussates to innervate the contralateral SO muscle
what is the only CN to leave the dorsal side of the midbrain and decussate to unnerve the contralteral EOM
4
Contra SO
Anatomical origin of SO
Lesser wing
The physiological origin of the SO
Trochlea
The _____ are the only EOMs to receive innervation from the contralteral Cn nuclei
SR and SO
V1
Provides sensory information from the head to the tip of the nose
V2
Provides sensory info from the side of the nose to the mouth
V3
Provides sensory info from the the head and ear to the mandible. It also provides motor info to the muscles of mastication
How do the sensory fibers travel for Cn V
‣ The sensory fibers travel from the face and head structures, through the cavernous sinus and synapse in the trigeminal ganglion (posterior portion of the cavernous sinus) before traveling to the sensory nuclie in the pons to relay to the thalamus.
What are the sensory nucleus of the trigeminal nerve
- Spinal nucleus: medulla, pain and Temp from ipsilateral face
- Main sensory nucleus: pons, light touch
- Mesencephalic nucleus: pons, mediates proprioception
Herpes and V1
• Herpes simplex keratitis can affect any or all of the branches of V1. This, these patients are much more likely to have involvement of the upper eyelid and forehead rather than the lower eyelid and forehead
V1 branches
Nasociliary
Frontal
Lacrimal
Nasocilairy nerve
V1
sensory info from the cornea, iris, and tip of the nose. It has several branches including the long ciliary nerves, short ciliary nerves, intfratrochlear nerves, and the anterior and posterior ethmoid nerves
• The LPCNs: sensory to cornea, iris, Ciliary muscle. Sympathetic fibers to the dilator muscle of the iris
• SPCNs: sensory fibers to cornea, iris, ciliary muscle
• Infratrochlear nerve: sensory fibers to the medial angle of the eyelids
Branches of nasociliary nerve
◦ Branches from the nasociliary nerve of V1 innervate the cornea and the tip of the nose. This explains why Hutchinson’s sign indicates a high likelihood of corneal involvement in herpes zoster
Frontal nerve
V1
branches in the cavernous sinus just before it enters the orbit through the superior orbital fissure. The frontal nerve divides into two terminal branches
Branches of the frontal nerve
Supratrochlear
Supraorbital
Supratrochlear nerve
Frontal branch
passes just superior to the trochlea of the SO to ultimately provide sensory innervation for the skin and muscles of the forehead and the medial portion of the upper eyelid and conjunctiva
Supraorbital nerve
Branch of the frontal
provides for the forehead and scalp, the central portion of the upper eyelid and the conjunctiva
Lacrimal nerve
Branch of V1
sensory feedback for the lacrimal nerve
• Just before it enters the lacrimal gland, the lacrimal nerve receives parasympathetic fibers of CN VII from the zygomatic branch of V2; these fibers are responsible for lacrimation
• Once it leaves the lacrimal gland, the lacrimal nerve pierces the orbital septum to supply the lateral conjunctiva and ther lateral part of the upper eyelids
V2
Maxillary division
‣ Travels along the inferior lateral portion of the cavernous sinus before entering the foramen rotundum of the greater wing of the sphenoid. V2 divides into two terminal branches just before entering the orbit through the inferior orbital fissure
Branches of the maxillary nerve
Infraorbital nerve
Zygomatic nerve
Infraorbital nerve
Branch of V2
‣ Travels along the inferior lateral portion of the cavernous sinus before entering the foramen rotundum of the greater wing of the sphenoid. V2 divides into two terminal branches just before entering the orbit through the inferior orbital fissure
Zygomatic nerve
Branch of V2
courses laterally from the inferior orbital fissure and divides into the terminal branches that innervate LATERAL structures, including the lateral aspect of the forehead, the lateral side of the cheek, and the lateral aspect of the lower eyelid. Remember, the zygomatic nerve of V2 carries parasympathtic fibers from the pterygopalatine ganglion of CN VII to the lacrimal nerve of V1 to stimulate lacrimation
Nerve supply to the lower eyelid from lateral to medial
zygomatic, maticofacial, infraorbital, infratrochlear. Note that the infratrochlear nerve (a branch of the nasociliary nerve) provides nerve supply to the medical portion of the lower lid (majority) and the upper lid
V3
Mandibualr branch
‣ Provides sensory innervation to the lower face
‣ Provides motor innervation to the muscles of mastication
CN VI-abducens
◦ Located in the pons. Fibers leave the nucleus between the pons and medulla and then make a tight bed over the petrous ridge of the temporal bone before entering the cavernous sinus
Which nerve can be compressed most from increased ICP
CN 6
CN VI palsy can also result from an ICA aneurysm with the cavernous sinus due to the close association between the ICA and the CN VI as they travel through the cavernous sinus
If someone has a CN 6 palsy, what way is their head going to turn
Toward the affected side
CN VII
◦ Motor innervation to the muscles of facial expression and supplies parasympathetic fibers to the inner ear and facial glands (including lacrimal gland). The facial nerve also carries taste sensation (sensory) from the anterior 2/3 of the tongue
Voluntary motor root of CN VII
innervated the facial muscles, including the orbicularis oculi to close the eye
Involuntary motor root of CN VII
parasympathetic fibers stimulate secretion of the facial glands including lacrimation of the lacrimal gland. The involuntary motor root also provides a branch to the stapedius muscle of the middle ear to dampen sound
Sensory root of Cn VII
carries taste form the anteiror 2/3 of the tongue
Course of CN VII
‣ Input to CN VII nucleus begins in the precentral motor cortex in the frontal lobe
‣ Fibers descend within the corticobulbar tract to the pons where the facial motor nucleus and the superior salivatory/lacrimal nuclei are located
‣ Fibers exit the nuclei of CN VII as a main motor root and the nervous intermediate root ( carries parasympathetic fibers of CN VII). Fibers arc around the abducens nucleus before exiting the brainstem. They enter the internal auditory canal in the petrous portion of the temporal bone and travel trough the geniculate ganglion
‣ After leaving the geniculate ganglion, the greater petrosal nerve and the chorda tympani nerve branch off the main root of CN VII. The remaining fibers exit the temporal bone of the skull through the stylomastoid foramen. They enter the parotid gland and divide into 5 branches to innervate the muscles of facial expression
Any nuclear lesion of CN VI may also damage
CN VII due to the close associated between the two nuclei within the brainstem
Greater petrosal nerve
Cn VII
‣ Carries parasympathetic innervation to the lacrimal gland. The greater petrosal nerve joins the deep petrosal nerve ( contains post ganglion sympathetic fibers) to form the Vidian nerve
‣ The vidian nerve travels to the pterygopalatine ganglion were parasympathetic fibers synapse
‣ Post ganglion fibers leave the pterygopalatine ganglion and join the zygomatic branch of V2. The zygomatic branch sends a communicating branch to the lacrimal nerve of V1 to innervate the lacrimal gland
Chorda tympani nerve
Cn VII
‣ Terminal branch of Cn VII that carries taste fibers to the anterior 2/3 of the tongue and provides parasympathetic supply to the submandibular and sublingual glands
Facial expression of CN VII
‣ The main root of CN VII passes through the stylomastoid foramen and enters the parotid glands, where it divides into the 5 branches (temporal, zygomatic, buccal, mandibular, and cervical branches) to supply the muscles of facial expression. The tow most superficial branches (temporal and zygomatic) innervate the muscles around the eye
• The temporal branch innervated the procerus, corrugator, occipital frontalis, and the orbicularis occuli
• The zygomatic branch innervated the orbicularis oculi
Facial nerve branching in the parotid gland and innervation
• Although the facial nerve branches within the parotid gland, it DOES NOT innervate the gland. The glossopharyngeal nerve (CN IX) provides innervation to the parotid gland. Removal of an acoustic neuroma may result in damage to the nearby parotid gland and CN VII, causing facial paralysis on the affected side
Bell’s palsy
‣ Remember that the upper neurons of CN VII in the brainstem receive bilateral input from the cerebral cortex. The lower neurons of CN VII receive contralateral input and provide innervation to the ipsilateral facial muscles
‣ Bell’s palsy: an idiopathic lesion of the lower motor neurons of Cn VII that result in impaired innervation to the upper and lower ipsilateral facial muscles, causing drooping of the mouth, and poor eyelid closure. Can result in paralytic lagophthalmos and secondary exposure keratopathy
Always ipsilateral, all of face
Stroke
‣ Remember that the upper neurons of CN VII in the brainstem receive bilateral input from the cerebral cortex. The lower neurons of CN VII receive contralateral input and provide innervation to the ipsilateral facial muscles
-a supranuclear lesion results in impaired innervation to the contralateral muscles of the lower face, often resulting in drooping of the mouth. The contralateral fibers to the upper face that allow eyelid closure and wrinkling of the forehead are after spared, and patient’s are able to firmly close their eyes and wrinkle their forehead
Always contralateral, lower side of the face
Parasympathetic innervation
• originates from the midbrain ( CN III) and the pons (CNVII) and performs 3 major functions
◦ Oculomotor nerve: travels to the iris sphincter and the ciliary muscle for miosis and accommodation
◦ Facial nerve: travels to the lacrimal gland for lacrimation
Sympathetic innervation
• 1st order preganglionic fibers begin in the hypothalamus and descend to the C8-T2 region of the spinal cord to synapse in the ciliospinal center of budge. 2nd order pre ganglionic fibers leave the ganglion and travel around the clavicle and across the apex of the lung before entering the sympathetic chain of ganglia around the neck. Fibers ascend the chain and synapse in the superior cervical ganglion. Post ganglionic fibers from the SCG form a plexus around the ICA and enter the skull via the carotid canal
Once inside the orbit, the post ganglionic sympathetic fibers within the ICA plexus may follow three routes
◦ 1. Follow the superior division of CN III to innervate mullers muscle of the upper eyelid
◦ 2. Follow the nasociliary nerve of CN V1 and branch with either the LPCNs or SPCNs
‣ LPCNs: to the iris dilator and the ciliary muscle
‣ SPCNs: choroidal and conjunctival blood vessels
◦ 3. Provide innervation to the blood vessels of the lacrimal gland (causing vasoconstriction) through the vidian nerve (the motor root of the pterygopalatine ganglion)
Hyperactive sympathetic innervation to the blood vessels of the choroid
thought to play a role in the development of central serous chorioretinopathy by contributing to localized damage in Bruch’s membrane
Summary of SPCNs and LPCNs
‣ SPCNs: originate from the ciliary ganglion and carry post ganglionic symptthetic and parasympathic fibers to various anteiror structures within the eye. They also carry sensory info from the eye back to the CG via the nasociliary nerve
‣ LPCNs: branch from the nasociliary nerve of V1 as it crosses the optic nerve. They carry post ganglionic sympathetic fibers to the eye, as well as sensory information from the eye back to the trigeminal ganglion
‣ Sensory information carried by both the SPCN and LPCNs is eventually taken to the trigeminal ganglion for analysis
Composition of the ON
• composed of axons of ganglion cells
• Courses to 3 destinations
◦ Midbrain, LGN, superior colliculus
Where does the ON go
◦ Midbrain, LGN, superior colliculus
Introrbital portion of the ON
surrounded by pia, arachnoid, and dura membranes that are continuous with the meninges of the cranium
◦ The subarachnoid space (between the arachnoid and pia sheaths) of the optic nerve is continuous with the subarachnoid space of the cranium and contains CSF
◦ The dura and arachnoid meninges fuse together and become continuous with the periorbita and the sclera; they DO NOT continue with the intracranial portion of the optic nerve (only the pia mater surrounds the intracranial optic nerve)
Papiledema
results from increased ICP that causes CSF within the subarachnoid space to leak over the superficial optic disc. The disc margins are blurred in papilledema because the CSF spreads over the margins into the surrounding RNFL
Oligodendrocytes and the ON
provide myelination to the axons posterior to the lamina cribrosa. Astrocytes provide structural support to the optic nerve axons
Schwann cells and the ON
not found within the optic nerve and therefore DO NOT provide myelination to the optic nerve
Optic sheath and EOM sheaths
‣ The optic nerve sheath is attached to the sheaths surrounding the SR and MR muscles. This association explains why appx 90% of patients with optic neuritis experience pain on eye movement
Blood supply to the retinal NFL
SPCA and the CRA
Blood supply to the intraocular portion of the ON
supplied by the circle of zinn (SPCAs) and other branches of the SPCAs
Blood supply to the introrbital ON
supplies by the branches from the CRA and the pial mater arterial plexus
Blood supply to the intracranial ON
branches of the ophthalmic, anteiror cerebral, anterior communicating, and ICA
Innervation to the blood supply to the ON
the optic nerve is able to auto regulate its blood supply (like the retina but unlike the choroid)
• the most anterior potion of the optic nerve. It is located in the nasal retina 15 degrees carom fixation and subtends an angle of 5-7 degrees
Optic disc
Shape of the disc
slightly larger vertically (1.75mm) than horizontal (1.50mm)
ON in the VF
acts like a blind spot in the VF because it DOES NOT contain a any PR (only NFL and glial membrane produced by astrocytes)
What type of glial cells are present in the ON
there are NO muller cells over the optic disc. Instead, astrocytes cover the optic disc and form the ILM of Elschnig
How long is the ON
50-60mm
Intraocular portion of the ON
1mm
‣ Portion of the ON that extends from the optic disc to the lamina cribrosa. Can be divided into 2 sections
What are the two sections of the intraocular portion of the ON
Pre laminar
Laminar
Prelaminar portion of the intraocular portion of the ON
anteiror the lamina cribrosa. NO MYELIN
◦ The optic nerve fibers are separated from the surrounding retinal tissue by a ring of glial tissue known as the intermediary tissue of Kuhnt. This glial tissue continues posteriorly as the border tissue of Jacoby and separates the optic nerve fibers from the choroid. Scleral collagen fibers at this level also surround the glial tissue, forming the border tissue of Elschnig
◦ Tight junctions within the glial tissue helps to protect the optic nerve fibers from fluid that leaks from the fenestrated chorodial vessels
What part of the ON has no myelin
Prelaminar intraocular portion
Laminar intraocular portion of the ON
section that exits the globe through the lamina cribrosa, a network of collagen and elastic fibers that bridge across the posterior scleral foramen and help support the optic nerve
Infraorbital portion of the ON
30mm
‣ Extends postierorly from the lamina cribrosa unit it exits the orbit via the optic canal. This portion of the ON is S-shaped and the axons are separated by CT septae, allowing for eye movements without damage to the ON
• The optic nerve axons posterior to the lamina cribrosa become myelinated by oligodendrocyte. The axons are also covered by the meninges that cover the rest of the brain
Intracanalicular portion of the ON
6-10mm
Portion running through the optic canal
Intracranial portion of the ON
10-16mm
Portion extendin ffrom the optic canal to the optic chiasm
Fibers of the optic nerve travel to these different locations
◦ 90% of the optic nerve fibers synapse in the LGN before traveling to the primary visual cortex
◦ Fibers traveling to the superior colliculus aid in saccadic eye movements
◦ Fibers traveling to the pretectal nucleus aid in pupil movement
Papillomacular bundle: visual pathway
composed of the fibers from the macula that enter the temporal side of the optic disc. Damage to these fibers can result in central, centric eval, and paracentral visual field defects
Central scotoma is often caused by
macular disease, vit optic nerve disease that affects the papillomacular bundle will also cause reduced visual acuity (nutritional/toxic neuropathy)
Nasal fibers
axons from retinal ganglion cells nasal to the optic nerve that tenure the nasal side of the disc
Superior and inferior arcuate fibers
axons from ganglion cells temporal to the fovea that enter the disc at the superior and inferior poles, respectively
ISNT rule
describes the comparative thickness of the rim tissue, with the inferior rim being thickest and the temporal rim being thinnest
What fibers cross at the optic chiasm
Superior and inferior nasal fibers
Anterior knee of willebrand
inferior nasal fibers that cross through the optic chiasm and then loop anteriorly into the contralateral optic nerve before entering the optic tract
Posterior knee of willebrand
superior nasal fibers that loop posteriorly into the ipsilateral optic tract before crossing through the optic chiasm
How do the nasal fibers cross in the optic chiasm
‣ The optic tract contains fibers that travel from the optic chiasm to the LGN. Note how the posterior knee (which contains the superior fibers) comes to the medial side of the left optic tract, while the anterior knee (containing inferior fibers) courses to the lateral side of the tract. Macualr fibers are protected in the middle of the tract
Optic chiasm
located within the circle of Willis. The ICA and posterior communicating arteries travel along the lateral edges of the optic chiasm. The pituitary gland is located inferior to the optic chiasm
Optic tract
extends from the optic chiasm to the LGN and contains fibers (crossed and uncrossed) from each eye that provide information from the same side of the visual field. The optic tract travels along the lateral surface of the cerebral peduncle parallel to the posterior cerebral arteries
Right optic tract
‣ Superior fibers (nasal and temporal) course to the medial side of the optic tract. The medial portion of the right optic tract contains right superior temporal and left superior temporal nasal fibers
‣ Inferior fibers course to the lateral side of the optic tract. The lateral potion of the right optic tract contains right inferior temporal and left inferior nasal fibers
‣ Macular fibers travel in the middle of the tract
LGN
• fibers within the optic tract synapse at the LGN located within the thalamus. Remember that appx 90% of optic nerve fibers synapse at the LGN before projecting to the primary visual cortex. The LGN is composed of 6 layers that contains three cell types
What are the three cell types of the LGN
◦ 1. Magnocellular layers: layers 1 and 2, contain large magno cells
◦ 2. Parvocellular layers: layers 3-6, contain medium parvo cells
◦ 3. Koniocellular layers: contain small cells located between each layer
Crossed fibers of the optic tract synapse in what layers of the LGN
1,4,6
Uncrossed fibers of the optic tract synapse in what layers of the LGN
2,3,5
The fibers of the optic tract synapse in what orientation
Superior fibers synapse medial LGN, inferior fibers synapse lateral LGN
Macular fibers form a wedge of synapses at the dorsal edge of the LGN and extend throughout its entire thickness
SMIL
Superior fibers=medial
Inferior fibers-Lateral
What all does the LGN do
‣ In addition to serving as the location of the first synapse within the post optic nerve portion of the visual pathway, the LGN also receives fibers from subcortical areas and the primary visual cortex to help fine tune the visual information that is relayed to the primary visual cortex.
The fibers that leave the LGN and travel to the primary visual cortex are called
The optic radiations
Inferior radiations
composed of the inferior retinal fibers from the lateral side of the LGN. These fibers travel through the temporal lobe and around the tip of the lateral ventricle into the parietal lobe (forming Meyer’s loop) before terminating in V1 in the occipital lobe.
Superior radiations
composed of the superior retinal fibers from the medial side of the LGN. These fibers course directly posterior through the inferior parietal lobe before terminating in V1 in the posterior portion of the occipital lobe
Primary visual cortex
primary visual cortex (V1/Broadmans area 17/striate cortex) is located on the medial surface of the occipital lobe. The calcarine fissure divides the internal posterior portion of the occipital lobe into anterior and posterior sections
Cuneus Gyrus
the superior portion of the visual cortec in the occipital lobe. Superior retinal fibers terminate here
Lingual Gyrus
inferior portion, inferior fibers terminate here
Macular fibers
project to the outer surface of the apex of the occipital lobe and make up appx 50% of the fibers within V1
Superior macular fibers project to
Cuneus gyrus
Inferior macular fibers project to
Lingual gyrus
Summary of the inferior retinal fibers
lower fibers (inferior fibers) course laterally in the optic tract and form Meyer’s loop before ending in the Lingual gyrus
Contents of the primary visual cortex
◦ Contains myelinated nerve fibers that mainly project from the LGN, as well as fibers from the superior colliculus and the frontal eye fields. It is organized into 6 horizontal layers and multiple vertical columns of neurons
Layer 4 of V1
location of the synapses beterrn the optic radiations and the neurons in the striate cortex. Fibers from the parvo and magnocellular layers of the LGN synapse in different strata within layer 4. Axons projecting from the neurons within layer 4 of V1 travel to higher cortical areas for further visual information processing
Layer 5 of V1
sends axons to the superior colliculus for control of saccadic eye movements
Layer 6 of V1
provides feedback information back to the LGN
Ocular dominance columns in V1
‣ Vertical columns of cells are organized into ocular dominance columns that contain fibers from only one eye. Ocular dominance columns are further organized into stimulus orientation columns.
When does binocular processing of visual information begin (what part of the pathway)
V1
Blood supply of the optic chiasm
supplied by the circle of Willis and branches of the ICA
Blood supply of the optic tracts
anteiror choroidal branch of the MCA
Blood supply to the LGN
anterior choroidal and PCA
Blood supply to the optic radiations
anterior choroidal, MCA, and PCA
Primary visual cortex blood supply
PCA and the MCA
‣ The PCA and the MCA serve as a dual blood supply to the primary visual cortex. If one arterial blood supply is blocked (stroke), vision is often spared because the 2nd arterial blood supply is still able to provide nutrients and O2 to the visual cortex
If there is a tumor in the occipital lobe that does not spare the macula
Tumor is compressing both the MCA and PCA
If blood supply to one side of the visual cortex is blocked
Macular sparing because there is another blood supply
STROKES are macular sparing
Which are macular sparing, strokes or tumors
Srtrokess
Post chiasmal lesions
produce homonymous visual field defects. This means that the same side of the visual field is affected in both eyes
◦ A right post chiasmal lesion will result in the loss of the left VF in the right AND left eye
The more posterior a post chiasmal lesion is located
the more congruous the visual field defects are between the eyes
◦ Congruity refers to the similarity between homonymous defects in each eye. Remember that fibers from each eye carry visual information about a particular point in the VF travel closer together as they travel more posterior in the visual pathway. Thus, these fibers are often damaged together, producing VF defects with a similar size and shape between the two eyes
Occipital lobe lesions cause what kind of defects, congruous or noncongruous
congruous defects because it is the most posterior location within the visual pathway
Incongurous VF defects
are homonymous defects that DO NOT have a similar size and shape between the two eyes. Lesions that are more anterior in the visual pathway cause incongruous field defects
Complete homonymous hemianopsia
describes a defect involving one half of the visual field. The location of the lesion cannot be determined based on the appearance of the VF defect, as a lesion anywhere along the visual pathway may result in this type of VF loss. Thus, a complete defect CANNOT be described as congruous or non-congruous. Congruity is reserved for INCOMPLETE homonymous VF defects
Temporal lobe lesions
superior VF defects. This is often referred to as “pie in the sky”: defect. Remember that a lesion in the temporal lobe damages the inferior retinal fibers forming Meyer’s loop.
Parietal lobe lesions
inferior visual field defects. This is often referred to as “pie on the floor” defects. Remember that a lesion in the parietal lobe damages superior retinal fibers (and is also associated with asymmetric OKN response)
How to remember what kind of VF defect is caused by partietal and temporal lobe lesions
PITS
- parietal=inf VF
- temporal=superior VF
VA in post chiasmal lesions
unaffected in post chiasmal lesions unless bilateral lesions are present. Remember that in order for VA to be affected, the macular region of the occipital lobe has to lose BOTH of its blood supplies
The macular region of the visual cortex blood supply
dual blood supply from the MCA and the PCA
A macular involving VF defect will occur only if
BOTH PCA and MCA are affected
◦ If only one blood supply is affected, vision will remain unaffected (macular sparing) because the other blood supply will continue to provide nutrients to the macular fibers within the occipital lobe
Macualr sparing homonymous hemianopsia
most commonly resutls from a stroke that has affected either the MCA or the PCA (but not both). It is very rare for a stroke to affect BOTH blood supplies of the superficial occipital lobe
Macula only homonymous hemianopsia
most commonly occurs from a tumor that has compressed BOTH blood supplies to the macular cortex. Although it can results from multiple strokes that affect the MCA and the PCA, this is extremely rare
Bitemporal hemianopsia
classically caused by a pituitary gland tumor that compresses the nasal fibers from each eye that cross at the optic chiasm
Optic chiasm lesion that extends towards one of the optic nerves
causes a junctional scotoma. This often appears as central vision loss in one eye and superior temporal vision loss in the fellow eye
‣ The eye with the affected optic nerve will have very poor VA. The other eye will have minimal damage (and good VA) because the anterior knee of WIlbrand loops into the damaged optic nerve
Bitemporal defects or junctional scotoma
indicate a lesion at the optic chiasm
VF defects that respect the horiztonal midline
result from lesions anteiror to the chiasm and are most commonly due to glaucoma
VF defects that respect the vertical midline
result from post-chiasmal lesions and are most commonly due to strokes
90% of homonymous hemianopsia are from
strokes. The main exception occurs with macula only homonymous hemianopsias, which are rarely caused by strokes (think compressive lesion!)
Optic nerve lesions
◦ Cause asymmetric VF loss between the eyes
◦ Defects typically respect the horizontal midline
◦ Defects may be bilateral but they are NOT congruous
◦ An APD can occur if asymmetrical damage between the optic nerves is great enough
◦ VF defects will correspond to the location of the lesion within the retinal nerve fiber layer
Unilateral defect, binasal step, and/or arcuate scotoma
retinal or optic nerve pathology
Retinal lesions VF loss
◦ Causes asymmetrical vision loss between the eyes
◦ Defects DO NOT respect the horizontal or vertical midline
◦ Defects may be bilateral but they are NOT congruous
