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
