8b – Anatomy of the Eye II Flashcards by Danielle Groenendijk

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)

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Ocular muscles: oblique muscles

-dorsal and ventral
-rotate eye to CORRECT direction due to recti muscles
*tendon inserted near vertical equator

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Dorsal oblique muscle originates from:

-apex of orbital cone
-deflects around TROCHLEA (acts like a pulley)

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Retractor bulbi muscle:

-pull eye back into orbit
-tendon inserted POSTERIOR to vertical equator
-absent in humans

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Retractor bulbi muscle in ox:

-form a COMPLETE circle around optic nerve

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Retractor bulbi muscle in dog:

-multiple single muscles

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Eyelids (palpebrae) consist of:

-skin
-musculofibrous layer
-mucous membrane (palpebral conjunctiva)

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Skin of palpebrae:

-thin
-delicate
-TACTILE hair (cilia, eyelashes)

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Cilia in dogs and cats:

-dogs: only present in upper lid
-cats: neither upper or lower lids

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Upper palpebrae:

-more extensive and mobile
>medial and later angles meet at palpebral FISSURE

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Roots of cilia associated with:

-small ciliary and sebaceous glands
*INFLAMMATION of gland=stye

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Musculofibrous layer formed by:

-orbicularis oculi
-orbital SEPTUM
-aponeurosis of levator muscle

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Orbicularis oculi:

-lies directly under skin
-closes eyelids

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Tarsus: palpebrae

-plate-like fibrous continuation of orbital septum
-STABILIZES edge of lid

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What lines the edges of palpebrae?

-a row of 20-40 small holes
>open a series of tarsal glands that secrete fatty material

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Lacrimal puncta:

-open near medial angle
-part of lacrimal system

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Part Two

Third eyelid:

-nictitating membrane
-conjunctival FOLD between lacrimal caruncle and eyeball
-invisible when eye is closed

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Nictitating membrane is covered:

-with conjunctiva on BOTH SIDES

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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

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Third eyelid is kept retracted by:

-smooth muscle (orbitalis)

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Third eyelid is innervated by:

-sympathetic fibers

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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

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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:

1. Supplying eyeball, penetrate SCLERA to reach uvea and retina 2. Supplying OCULAR muscles 3. 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