Orbit and Ocular Adnexa Flashcards
What is the Volume of each Eye?
30 cm Cubed
What is the shape of each orbit?
Pear-Shaped (ON represents the Stem)
What are the dimensions of the orbital Entrance? And where is the largest part of the orbit located?
Dimensions of entrance are 35 mm tall x 45 mm wide. Largest part of the orbit is located 1 cm posteriorly from entrance
What are the bones of the orbit?
Frontal, Palatine, Sphenoid, Ethmoid, Lacrimal, Maxillary, and zygomatic
What are the bones of the orbital roof?
Orbital Plate of the Frontal Bone and Lesser Wing of the Sphenoid
What are the bones of the medial orbital wall?
Frontal Process of the Maxillary Bone; lacrimal bone; orbital plate of ethmoid bone; lesser wing of sphenoid bone
What bone makes up the largest portion of the medial orbital wall?
Ethmoid bone
What are the bones that make up the orbital floor?
Maxillary bone; palatine bone; orbital plate of zygomatic bone
What bones make up the lateral wall of the orbit?
zygomatic bone; greater wing of sphenoid
What is the strongest wall of the orbit?
Lateral Wall
What is Whitnalls Tubercle? Where is it located? What attaches to the tubercle?
= small elevation on the orbital margin of the zygomatic bone.
Serves as site of attachment for:
- Lateral Rectus Muscle Ligament
- Lockwood Suspensory Ligament (aka suspensory ligament of the eyeball)
- lateral palpebral ligament
- levator aponeurosis
- whitnall ligament
What is transmitted through the Optic Foramen?
Leads from middle cranial fossa to apex of orbit, passing through lesser wing of sphenoid; transmitting ON, Ophthalmic artery, and sympathetic fibers from carotid plexus.
Superior Orbital Foramen
Located on medial 1/3 if superior margin of orbit
Transmits blood vessels and supraorbital nerve (branch of CN V1)
Anterior Ethmoid Foramen
located at frontoethmoidal suture.
Transmits Anterior Ethmoidal Vessels and nerve
Posteror Ethmoid Foramen
Located at junction of roof and medial orbital wall
Transmits Posterior Ethmoidal Vessels and nerves through the frontal bone
Zygomatic Foramen
Located in the lateral aspect of the zygomatic bone
Transmits zygomaticofacial and zygomaticotemporal branches of zygomatic nerve and artery
Where does the Nasolacrimal Duct travel?
Inferiorly from lacrimal fossa into the inferior meatus
Infraorbital Canal
Continues anteriorly from the infraorbital groove and exits 4 mm below inferior orbital margin
Transmits infraorbital nerve (branch of CN V2)
Superior Orbital Fissure
Located b/w wings of sphenoid bone, lateral to and partly above/below ON
is 22 mm long and spanned by tendinous annulus of Zinn
What structures are transmitted above the annulus of Zinn?
Lacrimal Branch of CN V1
Frontal Branch of CN V1
Trochlear Nerve (CN IV)
Superior Ophthalmic Vein
Mnemonic: LFTS
What structures are transmitted through the annulus of Zinn?
Superior and Inferior Divisions of CN III
Nasociliary Branch of CN V1
Sympathetic Roots of Ciliary Ganglion
Abducens Nerve (CN VI)
Path of the inferior ophthalmic vein?
Variable, may be transmitted either through or below annulus of Zinn, or through interior orbital fissure. Eventually connects with pterygoid plexus before draining into cavernous sinus.
Inferior Orbital Fissure
located below SOF b/c lateral wall and floor of orbit
Transmits infraorbital and zygomatic branches of CN V2, an orbital nerve from pterygopalatine ganglion, and possibly inferior ophthalmic vein
Significance of Peri-orbital sinuses?
provide a route for the spread of infection
How many cranial nerves directly innervate the eye and peri-ocular structures?
6 of the 12 cranial nerves
Ciliary Ganglion
Located 1 cm in front of the annulus of Zinn on the lateral side of the Ophthalmic artery (b/w ON and LR)
What are the roots of the Ciliary Ganglion?
Long Sensory Root: arises from nasociliary branch of CN V1 (contains sensory fibers of cornea, iris, and ciliary body)
Short Motor Root: arises from inferior division of CN III (fibers synapse on ganglion, and post-ganglionic fibers carry parasympathetics to iris)
Sympathetic Root: comes from plexus around ICA (innervates ocular blood vessels and dilator muscles of iris)
**Only parasympathetic fibers synapse
What do the roots of the ciliary ganglion combine to form?
the Short Ciliary Nerves
Short Ciliary Nerves
exist as 2 groups of 6-10 fibers arising from the ciliary ganglion, traveling on either side of the ON
Pierce sclera around the ON (along with long ciliary nerves)
pass anteriorly between the choroid and the sclera unit the ciliary muscle forming the plexus that supplies the cornea, ciliary body, and iris
Where do the 4 rectus muscles insert?
Into the globe
What is the spiral of Tillaux?
formed by the progressively lengthening insertions of the rectus muscles around the limbus
What are the distances from the limbus for the rectus muscles?
MR: 5.5 mm
IR: 6.5 mm
LR: 6.9 mm
SR: 7.7 mm
The Annulus of Zinn consists of what?
is made up of superior and inferior tendons, and serves as the origin of the 4 rectus muscles
What do the upper and lower tendons of the annulus of zinn form?
Superior tendon: the SR, and portions of the MR and LR
Inferior Tendon: the IR, and portions of the MR and LR
Origin of the Levator Palpebrae Superioris
the lesser wing of the sphenoid bone at the apex of the orbit (superior to the annulus of sinn)
Origin of the Superior Oblique muscle
originates from the periosteum of the sphenoid bone (above and medial to optic foramen)
Origin of inferior oblique muscle
originates from a shallow depression located anteriorly in the orbital part of the maxillary bone
Blood Supply of the Muscles
Superior and Inferior branches of ophthalmic artery, lacrimal artery, and infraorbital artery
Lateral Rectus: supplied by a single vessel from the lacrimal artery
Other Rectus Muscles: 2 anterior ciliary arteries (communicate with major arterial arcade of the ciliary body via perforating scleral vessels)
What muscles are innervated by CN III?
Superior Division- SR and LPS
Inferior Division- IR, IO, and MR
What does CN IV (trochlear) innervate?
Superior Oblique muscle
What does CN VI (abducens) innervate?
Lateral Rectus
What is the nerve:muscle fiber ratio of the eye muscles? And why is this significant?
Ratio is between 1:3-1:5
This is significant b/c it allows for the precise ocular movements
The EOM consist of what type of muscle fibers?
Tonic slow type and fast twitch type.
Tonic, Slow type muscle fibers
Unique to EOM
innervated by multiple grape-like nerve endings (“En Grappe”)
used for smooth pursuit movements
Fast Twitch type muscle fibers
larger and located deeper within the muscles than the tonic slow type fibers
rapidly contract
innervated by plate-like nerve endings (en plaque)
aid in saccadic movements
What are the dimensions of the palpebral fissure?
27-30 mm long x 8-11 mm wide
How much can the upper eyelid be raised and by what muscle?
15 mm by the levator palpebrae superioris
how much additional widening can occur to the palpebral fissure, and by what muscle?
2 mm additional widening, performed by frontalis muscle
What are the layers of the eyelid from dermis inward?
Skin-> Eyelid Margin-> Subcutaneous CT-> Orbicularis Oculi-> Orbital Septum-> LPS-> Mullers muscle-> Tarsus -> Conjunctiva
Eyelid Skin
Thinnest skin in the body
Contains fine hairs, sebaceous glands, and sweat glands
What is the “Gray Line?”
aka “internarginal sulcus”, located along the entire length of the eyelid
corresponds to the most superficial portion of the orbicular is oculi (muscle of Riolan)
What is located anterior and posterior to the Gray Line?
Anterior: Eyelashes/Cilia
Posterior: openings to tarsal (meibomian) glands
The eyelid margins contain what glands?
Glands of Zeis= modified sebaceous glands associated with cilia
Glands of Moll= apocrine sweat glands of skin
How are the muscle fibers of the orbicular is oculi arranged?
in concentric bands around the palpebral fissure
What are the sub-divisions of the orbicularis oculi? What are the functions of each sub-division?
Orbital: acts as a sphincter, strictly voluntary
Pre-Septal: both voluntary and involuntary functioning in spontaneous and reflex blinking
Pre-Tarsal: plays a role in tear drainage
- firmly adheres to the tarsus and is partly attached to the Ant and Post Lacrimal Crests
Where do the pre-tarsal and pre-septal parts of the orbicularis oculi unite?
along the superior palpebral fissure
What is the muscle of Riolan?
a small bundle of striated muscle fibers of the orbicularis oculi extending to the eyelid margin
Orbital Septum
thin sheet of CT encircling the orbit as an extension of the periosteum of the roof/floor of the orbit
attaches to the anterior surface of the LPS as well as the levator aponeurosis
orbital fat located posterior to septum
provides a barrier to the anterior/posterior extravasation of blood or infection
Levator Palpebrae Superioris
body overlies the superior rectus
near the whitnall ligament, changes direction from horizontal to more vertical and divides anteriorly into aponeurosis and posteriorly into superior tarsal (mullers) muscle
Where does the aponeurosis insert into?
Anterior surface of Tarsus
Medially/laterally into canthal tendons
trochlea of superior oblique muscle
fibrous tissue bridging superior eyelid fold
What is the length of the LPS + Tendon?
50-55 mm long
What is Mullers Muscle?
smooth, sympathetically innervated muscle originating from the undersurface of the LPS in the upper eyelid
attaches to the upper border of the tarsus and to conjunctiva of upper fornix
What is the counterpart to Mullers muscle in the lower eyelid?
Capsulopalpebral muscle
Tarsal Plates
consist of dense CT
attached to orbital margins by medial and lateral palpebral ligaments
What is the difference between the upper and lower tarsus?
The upper tarsus is 3x wider then the lower tarsus, but identical in their other dimensions.
Upper: 29 mm long x 1 mm thick x 11 mm wide
Lower: 29 mm long x 1 mm thick x 4 mm wide
What kind of glands are located in the Tarsus?
modified oil-producing holocrine meibomian glands that are vertically oriented in parallel rows throughout the tarsus
upper eyelid–contains 30-40 orifices
Lower eyelid–contains 20-30 orifices
What is the palpebral conjunctiva?
a thin transparent vascularized membrane covered by non-keratinized stratified squamous epithelium that lines the inner surface of the eyelid
What is the vascular supply of the eyelid?
it is derived from both the internal (ophthalmic) and external carotid (facial) arteries, with the terminal branches of both systems anastomosing,
superficial and deep plexuses provide blood supply to upper and lower lids
What is the venous drainage of the eyelids?
Superficial system (Pre-Tarsal)– drains into internal and external jugular systems
Deep system (Post-Tarsal)- drains into cavernous sinus
Describe the lympathic drainage of the eye?
Lympathics are found in the eyelids and conjunctiva, but none in the orbit or eye itself.
drainage parallels venous drainage via 2 groups
1- medial group- drains into submandibular LNs
2- lateral group- drawings into superficial pre auricular LNs
What is the Caruncle?
a small fleshy ovoid structure attached to the inferomedial side of the plica semilunaris
contains sebaceous glands and fine colorless hairs
surface covered by non-keratinized stratified squamous epithelium
What is the Plica Semilunaris?
a narrow, highly vascular crescent-shaped fold of conjunctiva located lateral to and partly under the caruncle
epithelium is rich in goblet cells
is a vestigial structure (analogous to nictitating membrane of animals)
Location of Main Lacrimal Gland
located in a shallow depression within the orbital portion of the frontal bone
Parts of the Main Lacrimal Gland
divided into two parts by the levator aponeurosis
1- Main gland
2- Palpebral portion
Entrance point of excretory lacrimal ducts onto the eye
5 mm above superior margin of upper tarsus into the conjunctival fornix
Which part of the lacrimal gland should you biopsy if needed?
The main gland, as the ducts pass through the palpebral portion, you wouldn’t want to damage them during the biopsy.
Function of the lacrimal gland
is an exocrine gland that produces serous secretions
What cell types make up the lacrimal gland?
Acinar Cells- line lumen of gland
Myoepithelial Cells
What is the blood supply of the lacrimal gland?
supplied by the lacrimal artery, which is a branch of the ophthalmic artery
What is the innervation of the lacrimal gland?
Secretomotor cholinergic, vasoactive intestinal polypeptide (VIP)- ergic, sympathetic, and the lacrimal nerve (branch of CN V1)
Name the accessory lacrimal glands. Where are they located? Cytology? Production? Innervation?
Glands of Krause and Wolffring. Locared at the proximal lid borders or in the fornices. Cytologically identical to main lacrimal gland (acinar and myoepithelial cells). Similar innervation to main gland. Produces 10% of lacrimal secretory mass.
What is the diameter of the lacrimal punctum? And what is their orientation?
Diameter of the punctum is 0.3 mm, and oriented posteriorly toward the tear lake.
What are the distances from the medial canthus for the upper and lower punctum?
The lower punctum is located 6.5 mm from the can thus, and the upper punctum is located 6.0 mm from the canthus. Disparity is due to formation of the maxillary sinus, which pulls the lower punctum laterally.
What is the path of drainage for tears?
Punctum->canaliculus->lacrimal sac->nasolacrimal duct-> nose
In what percentage of people do the upper and lower canaliculi join to form a common canaliculus?
90%
What is the conjunctiva?
a mucus membrane made of up non-keratinizing squamous epithelium with numerous goblet cells and thin highly vascularized lamina propria.
about 2 - 5 cells thick
What are the zones of the conjunctiva?
Palpebral, forniceal, and bulbar.
What is the palpebral conjunctiva?
covers the eyelids inner surface, begins at the mucocutaneous junction. Is firmly adherent to tarsus and freely mobile at fornices
What is the forniceal conjunctiva?
a freely mobile, redundant conjunctiva located at the fornices. Becomes enmeshed with fibrous elements of levator aponeurosis and mullers muscle.
What is the bulbar conjunctiva?
freely mobile conjunctive that fuses with tenons capsule and inserts into the limbus.
What is the blood supply of the conjunctiva?
Anterior Ciliary arteries, posterior conjunctival arteries (via proximal arcade), and branches of the marginal arcades of the lids.
Limbal blood supply derived from ciliary arteries via anterior conjunctival arteries.
What is the innervation of the conjunctiva?
derived from the ophthalmic division of CN V
What is Tenons Capsule?
envelope of elastic tissue that fuses posteriorly on the ON sheath and anteriorly on the inter muscular septum (located 3 mm posterior to limbus)
is the cavity in which the globe moves
composed of fibroblasts and collagen fibrils
Where is Tenons Capsule the thickest?
around the equator of the globe
Where do the EOM penetrate Tenons Capsule?
10 mm behind their insertions into the globe
What is the suspensory ligament of lockwood? What is its function?
created from fusion of the sheaths of the IR, inferior tarsal muscle, and check ligament of MR/LR
Provides support for the blogs and anteroinferior orbit
Posterior Ciliary Vessels
Originate from the ophthalmic artery and supply the entire uveal tract, cilioretinal arteries, sclera, margin of the cornea, and adjacent conjunctiva
How do the posterior ciliary arteries and nerves enter the globe?
In a ring around the ON
How do the long ciliary arteries and nerves enter the globe?
They enter on either side of the ON close to the horizontal meridian and pierce the sclera
Where do the Anterior Ciliary Arteries originate? What do the Anterior Ciliary Arteries supply?
They originate from the Ophthalmic Artery
They supply the SR, MR, and IR (usually in pairs)
Where does the blood supply of the LR come from?
a single lacrimal artery originates from a anterior ciliary vessel
Posterior Ciliary Vessels eventually form what structure? Where is it located? How is it arranged?
The inter muscular circle of the Iris (branches supply major arterial circle).
Lies within the apex of the ciliary muscle
Has a radial arrangement
What are the vortex veins?
veins that drain the venous system of the choroid, ciliary body, and iris (Uvea)
How many vortex veins are located in each eye? Where are they located? And where do they exit the eye?
each eye contains 4-7+ veins
usually located with at least one per quadrant
They exit the eye 14-25 mm posterior to the limbus bw the rectus muscles
How far are the ampulla of the vortex veins located from the ora serrate?
8-9 mm from the ora serrate.
Note: a circle connecting the ampullae roughly corresponds to the equator
