External Eye and Adnexa Anatomy Flashcards
What are the anatomical direction terms used in reference to the eye
Anterior, Posterior, Superior, Inferior
How does the placement of the bony orbit in the skull differ in carnivores vs herbivores and what is the effect of this on vision?
Carnivores: more rostrally
= more binocular, less peripheral vision, larger blind spot caudally
Herbivores: more laterally
= more peripheral, less binocular, small blind spot caudally but have small blind spot cranially as well
Which species have an incomplete orbit
What structure is present to “complete” the orbit
Carnivores and pigs
Have orbital ligament
the Pterygoapalatine fossa houses what anatomical structures?
Globe and adnexa
Formaina for arteries, veins, and nerves serving the globe/adnexa
Which cranial nerves supply the globe/adnexa
CN II (optic)
CNIII (oculomotor)
CN IV (trochlear)
CNV1 (ophthalmic)
CN VI (abducens)
(CNV2 [maxillary])
where is the supraorbital fossa and what anatomical structures are present there
Space dorsal and caudal to orbit
Houses: an extension of retrobulbar fat pad
coronoid process of mandible extends into this space
Clin sig of retrobulbar fat pad
EXTRA-prominent in horses
“blobs-in-and-out” when horses chew!
Last place in body for fat storage - shows starvation/cachexia
List the layers of the eyelid
Skin
Musculofibrous layer
Conjunctiva
What structures are in the skin layer of the eyelid
Cilia (eyelashes)
Sebaceous glands of cilia
Cilia species differences
Dogs - no lower eyelashes
Cats - no eyelashes at al! only fine hairs
Horses, Cows - prominent upper eyelashes, and also have lower eyelashes
What 3 structures are in the musculofibrous layer of the eyelid
Orbicularis oculi m
Orbital septum
Tarsus
What is the orbicularis oculi m, what does it do, and what is it innervated by?
Circumferential muscle - “purse-string”
Closes the eyelids
Innervated by CN 7, facial n
What is the orbital septum, where is it located, and what does it do?
Fibrous connective tissue
Arises from oribtal margin
Continuation of periorbita
What is the tarsus and what does it do?
aka tarsal plate
Thickened extension of orbital septum
Gives structure to lid margin - near the free edge of the lids that supports the free edge, prevents “flopping”
Has ligamentous attachments to the orbit medially and laterally
What are the palpebral ligaments and what do they do
ligaments anchoring the eyelids medially &
laterally so that they close in a horizontal “line” rather than a “circle” when the orbicularis oculi contracts
What is the levator palpebrae superioris m, what nerve innervates it and what does it do?
- narrow strip of muscle running longitudinally into upper lid
- contraction raises the upper lid
- innervated by CN III, which also innervates the muscle that rotates the eye upward (dorsal rectus m.)
- simultaneous contraction of the two muscles ensures that when the globe rotates upward, the upper lid is also raised
List the major muscles of the eyelid
Levatoir Palpebrae superiors
levator anguli oculi medialis
retractor anguli oculi lateralis
Superior tarsal m (aka Muller’s muscle)
What is the muller’s muscle and what innervates it? What will result if it is damaged?
aka superior tarsal muscle
smooth muscle functions to maintain the elevation of the upper eyelid. It receives sympathetic innervation.
Damage to this muscle, or the nerves which supply it, will result in ptosis of the affected eye as seen in Horner syndrome.
Describe the conjunctival layer. What is it made from? What cell type can be found here and what do they do? Describe species differences and what happens if it becomes inflamed.
Non keratinized epithelial layer
Thin and transparent
Goblet cells → mucin in the tear film
Also houses MANY microvessels and provides nutrition to eyelids and periphery cornea
lateral bulbar parts may be pigmented in some individuals, esp. Pugs, Eq, Bo
When inflamed vessels can become visible (bloodshot eyes)
What is the palpebral conjunctiva
Posterior surface of palpebrae
Anterior and posterior surfaces of the 3rd eyelid
the portion lining the eyelids
- the internal surface of the superior and inferior
palpebrae, AND outer surface of the third eyelid
What is the bulbar conjunctiva
Surface of anterior sclera
the portion covering the sclera (“white part of the eye”) and inner surface of the third eyelid
What is the conjunctival fornix
Reflection of conjunctiva from eyelid to eyeball
the “pocket” at the deepest point of the superior and inferior palpebrae where the palpebral conjunctiva reflects onto the globe to become the bulbar conjunctiva
What is the conjunctival sac
Space between palpebral conjunctiva and bulbar conjunctiva
What is the fibrous portion fo the musculofibrous layer
Orbital Septum
What structures are present in the tarsal plate and what do the do?
tarsal glands (aka melbomian glands)
a row of glands just deep to the upper and lower tarsal plates
open onto free margin of each lid by a series of tiny, just-grossly visible openings (row of teeny dots)
secrete one layer of the tear film (the oily layer)
What is the third eyelid
aka nictitating membrane, semilunar fold
Fold of conjunctiva surrounding a T shaped cartilage Bar of ‘T’ forms free edge of 3rd eyelid Stem of ‘T’ directed caudally into orbit between lower lid and globe
What glands and tissue are associated with the third eyelid, where are they located, and what species differences are there
“superficial” gland of the third eyelid
- present in all species
- lies at the base (deepest) part of the cartilage
- “stem of the “T”
- contributes to part of the tear film
associated glands of the third eyelid
deep (Harderian) gland of the third eyelid
- present in pigs and ruminants
Lymphoid tissue present on bulbar surface
How does the third eyelid move and species differences
held in retraction by tonic contraction of the orbitalis (smooth) muscle
the contraction is under sympathetic control (lack of sympathetic tone produces Horner’s syndrome)
- motion over the eye is passive
when eye is retracted (or retropulsed) into the orbit, the third lid slides over globe
In cat: skeletal muscle in 3rd eyelid so has voluntary control
What is cherry eye
prolapse of superficial gland of third eyelid
What three things make up tear film and what structures produe each?
external lipid layer - tarsal glands
Intermediate aqueous layer - lacrimal glands
Internal mucous layer - goblet cells in conjunctiva
Describe the tear pathway
Lacrimal gland proper -> Lacrimal ductules -> lacrimal lake (gland of thrid eyelid also releases tears here)-> superior puncta/inferior puncta -> lacrimal ducts -> lacrimal sac -> nasolacrimal duct -> nasal cavoty
List the categories of gland in the eye and what anatomical structues are in eachj
Lacrimal glands
- Lacrimal gland proper
- Gland of the 3rd eyelid
- Deep gland of the 3rd eyelid
Sebaceous glands
- Tarsal glands
- Ciliary glands
Mucus glands
- Goblet cells in conjunctiva
What glands are near the eyes in carnivores and clin sig
Zygomatic salivary gland - ventral to eyeball on floor of orbit
can get inflammed and rupture -> press on eyeball
What are the three layers of the orbital fascia
Periorbita
Superficial layer
Deep layer
What is the periorbita, what is it made of, where does it attach, what structures does it surround and what structures does it give rise to?
Conical sheath
Smooth muscles and connective tissue
Attaches around optic canal to orbital rim
Surrounds eye mm, vessels, nerves, lacrimal gland, fat
Gives rise rostrally to orbital septum and tarsi of eyelids
What is the orbitalis m, what does it do and what is it innervated by?
One of 3 smooth mm in the periorbita
Muscle fibers oriented circumferentially
Innervated by sympathetic nervous system
Action is to constrict the periorbita to maintain eyeball position in orbit
What is the superficial muscular fascia and what structures does it cover
loose connective tissue deep to periorbital that surrounds levator palpebrae superioris and lacrimal gland
What is the deep muscular fascia and what structures does it cover
aka Bulbar fascia, sheath of the globe, Tenon’s capsule, vagina bulbi
deepest of all “investing” layers and separates posterior globe from adnexa within the periorbita
blends with limbus of globe
surrounds each extraocular muscle and optic nerve
What is the episclea space and what is its purpose and clin sig
space between the globe and Tenon’s capsule allows the eyeball to rotate freely
Enucleation (sx removal of eyeball) is performed here with dissection of the globe away from the tenon’s capsule
Describe the orbital fat, its purpose, and clin sig
Intra-periorbital, Extra-periorbital
Serves as a protective cushion
within which the eyeball moves
Helps position globe in orbit
The last of fat stores to be utilized to meet energy needs -sunken eyes are a sign of cachexia
Which extra ocular muscles are innervated by CN3
Dorsal, ventral, and medial rectus
Ventral Oblique
Which extra ocular muscles are innervated by CN6
Lateral rectus, rectractor bulbi
Which extra ocular muscles are innervated by CN4
Dorsal oblique
Describe the retractor bulbi muscle, what it surrounds, what it does, species differences, and what it is innervated by
One muscle with 4 slips
Surrounds CN II Optic n
Innervated by CN VI Abducens n
Retraction of globe leads to passive protrusion of 3rd eyelid
Not present in primates or birds
Which extraocular muscles originate at the apex of the periorbita
All 4 Rectus mm
Dorsal oblique m
Retractor bulbi m
Levator palpebrae superioris m
Which extraocular muscles originate at the medial orbital wall
Ventral oblique m
Which extra ocular muscles insert anterior to the equator of the globe
All 4 Rectus mm
Both Oblique mm
Which extra ocular muscles insert posterior to the equator of the globe
Retractor bulbi m
Which extraocular muscles insert in the upper eyelid
Levtator palpebrae superioris
Which is the action of the rectus extraocular muscles
rotate the globe in the direction of their name along the horizontal or vertical axis
(ie dorsal rectus rotates the globe dorsally)
Which is the action of the oblique extraocular muscles
Rotate globe relaytive to longitudinal axis
The dorsal oblique m rotates the top of the globe medially (intorsion).
The ventral oblique m rotates the top of the globe laterally (extorsion).
action of retractor bulbi
Pulls globe caudally
Action of levator palpebrae superioris
lifts upper eyelid
What nerves supply sensory to the eyelid
CN V Trigeminal- Ophthalmic branch CN V Trigeminal- Maxillary branch
What nerves supply somatic motor to the extracular mm
CN III Oculomotor
CN IV Trochlear
CN VI Abducens
What nerves supply motor to the eyelid mm
CN III Oculomotor
CN VII Facial
What nerve supplues parasymp. to the lacrimal gland
CN VII Facial
What is the main artery to the eye
External ophthalmic aa
Describe the arterial supply to the eye
Common carotid a to
External carotid a to
Maxillary a to
External Ophthalmic a to
Ciliary aa (Anterior, posterior Long, short)
Describe the venous drainage to the eye
Satellite veins
Scleral venous sinus and plexus
- Site of resorption of aqueous humor
Vorticose veins
- Non-satellite veins draining the choroid
