8b – Anatomy of the Eye II Flashcards
Ocular muscles: recti muscles
-dorsal, ventral, lateral, medial
-angle eye in RESPECTIVE direction
-originate from APEX of orbital cone (around optic canal)
-tendon inserted anterior to vertical EQUATOR)
Ocular muscles: oblique muscles
-dorsal and ventral
-rotate eye to CORRECT direction due to recti muscles
*tendon inserted near vertical equator
Dorsal oblique muscle originates from:
-apex of orbital cone
-deflects around TROCHLEA (acts like a pulley)
Retractor bulbi muscle:
-pull eye back into orbit
-tendon inserted POSTERIOR to vertical equator
-absent in humans
Retractor bulbi muscle in ox:
-form a COMPLETE circle around optic nerve
Retractor bulbi muscle in dog:
-multiple single muscles
Eyelids (palpebrae) consist of:
-skin
-musculofibrous layer
-mucous membrane (palpebral conjunctiva)
Skin of palpebrae:
-thin
-delicate
-TACTILE hair (cilia, eyelashes)
Cilia in dogs and cats:
-dogs: only present in upper lid
-cats: neither upper or lower lids
Upper palpebrae:
-more extensive and mobile
>medial and later angles meet at palpebral FISSURE
Roots of cilia associated with:
-small ciliary and sebaceous glands
*INFLAMMATION of gland=stye
Musculofibrous layer formed by:
-orbicularis oculi
-orbital SEPTUM
-aponeurosis of levator muscle
Orbicularis oculi:
-lies directly under skin
-closes eyelids
Tarsus: palpebrae
-plate-like fibrous continuation of orbital septum
-STABILIZES edge of lid
What lines the edges of palpebrae?
-a row of 20-40 small holes
>open a series of tarsal glands that secrete fatty material
Lacrimal puncta:
-open near medial angle
-part of lacrimal system
Part Two
Third eyelid:
-nictitating membrane
-conjunctival FOLD between lacrimal caruncle and eyeball
-invisible when eye is closed
Nictitating membrane is covered:
-with conjunctiva on BOTH SIDES
Nictitating membrane is supported by:
-a T-shaped CARTILAGE
>bar lies in free edge of the fold
>stem points backwards into orbit medial to eyeball
Third eyelid is kept retracted by:
-smooth muscle (orbitalis)
Third eyelid is innervated by:
-sympathetic fibers
Position of third membrane:
-slides passively over eyeball when eyeball is retracted OR
-pushed into orbit
>cats can draw 3rd eyelids
>remain drawn in certain neurological disorders
Third eyelid is seen in:
-most domestic and wild animals
>even some primates (gorillas)
>not in HUMANS (semilunar fold is its remnant)
Role of third eyelid:
-provide added protection to the protruding eyes of animals
Third eyelids bulbar surface:
-subepithelial lymph nodules can be seen
>may become inflamed
Palpebral conjunctiva:
-thin, transparent mucous membrane forming posterior lid
Bulbar conjunctiva:
-continuation of the palpebral conjunctiva reflected at base of libs
>continues on sclera
Conjunctival sac:
-potential space between lids and eyeball
-fornices
Fornices:
-dorsal and ventral extremities of conjunctival sac
Pale conjunctiva suggests:
-anemia
-shock
-internal hemorrhage
Lacrimal apparatus consists of:
-lacrimal fluid
-lacrimal gland PROPER
-accessory lacrimal gland of 3rd eyelid
-(deep 3rd eyelid lacrimal gland in pigs and ox)
Lacrimal fluid:
-TEAR
-keeps conjunctiva clean and moist
-supplies nutrients to the cornea
Lacrimal gland proper:
-between eyeball and dorsolateral wall of orbit
-duct open in dorsal fornix
Lacrimal fluid is repelled by:
-fatty secretion of tarsal glands
Lacrimal lake:
-where fluid pools at medial angle
-shallow depression around lacrimal CARUNCLE
*fluid then drawn by capillary action via lacrimal puncta into lacrimal canaliculi and down into lacrimal sac then into duct system
Nasolacrimal duct:
-opens in nasal cavity/nostrils
Blood supply of orbit: humans
-mostly thru internal ophthalmic artery with optic nerve
Blood supply of orbit in domestic animals:
-MOSTLY thru external ophthalmic artery
>branch of maxillary artery
3 subdivision of external ophthalmic artery:
- Supplying eyeball, penetrate SCLERA to reach uvea and retina
- Supplying OCULAR muscles
- Leave orbit to supply adjacent structures
Arteries for uvea and retina:
-short posterior ciliary arteries
-long posterior ciliary arteries
-anterior ciliary arteries
-greater arterial circle of iris
Short posterior ciliary arteries:
-mainly to retina
Anterior ciliary arteries:
-anterior parts
Greater arterial circle of iris:
-anastomoses of all above to pupil and ciliary body, conjunctiva
-also nourish cornea by diffusion
Leave orbit to supply adjacent structures:
-lacrimal artery
-supraorbital artery (only in large animals: to upper eyelid)
-malar artery to eyelids
-external ethmoidal artery to ETHMOIDAL conchae
Nerve supply of the orbit:
-6 of 12 CRANIAL nerves wholly or partly supply the obit
>optic (II)
>oculomotor (III)
>trochlear (IV)
>abducens (VI)
>ophthalmic (V1)
>zygomatic n. (branch of V2)
>auriculopalpebral (VII)
Optic (II):
-sense of VISION
Oculomotor (III):
-somatic to most ocular muscles
>dorsal, medial and ventral recti
>ventral oblique
>levator palpebral superioris
>part of retractor bulbi
Trochlear (IV):
-DORSAL oblique
Abducens (VI):
-lateral retus
-retractor bulbi
Ophthalmic (V1) divides in orbit into 3 branches:
-lacrimal n
-FRONTAL n
-nasociliary n
Lacrimal nerve:
-to lacrimal gland
-skin above the lateral angle of eye
Frontal nerve:
-much of upper eyelid
-forehead
-frontal sinus
Nasociliary nerve:
-structures at medial angle
-frontal sinus
-horn in small ruminants
-long ciliary to posterior part of eyeball
>including cornea
-ethmoidal
Zygomatic n (branch of V2):
-lower eyelid and adjacent skin
*main nerve of horn in ox
Auriculopalpebral (VII):
-later becomes palpebral
-supply muscles of eyelids (EXCLUDING the levator palpebrae superioris)
Autonomic sympathetic innervation:
-dilates pupil
Autonomic parasympathetic innervation:
-constricts pupil
-accommodates lens for near focus
