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BIOL 2P95 (35)

Eye Movements

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Dirk De Clercq

Anatomy of the Eye and Eye Movements I. Anatomy a. Walls of orbit i. Pyramidal shaped; twice as deep as wide; ii. 45 degree angle between orbits; eyeball occupies only anterior half iii. lots of blood vessels and fat 1. shock absorber, cushion, lubricant, protects nerves/vessels 2. last place that fat pads will disappear in body iv. floor: maxilla, zygomatic, palatine v. medial: ethmoid, lacrimal, frontal (ethmoid =fragile bone, paper thin) vi. roof: frontal, sphenoid vii. lateral: zygomatic, sphenoid b. Orbital foramina i. optic canal: holds optic nerve and ophthalmic artery 1 ii. superior orbital fissure: CN III, IV, V , VI, ophthalmic veins (sup/inf) • ophthalmic veins communicate w/ cavernous sinus and facial vein iii. inferior orbital fissure: CN V from foramen rotundum iv. ethmoidal foramina: ethmoidal nerves pass thru medial wallnasal nn. v. fossa for lacrimal sac and nasolacrimal canal (inferomedial) c. Lacrimal gland i. superolateral part of orbit ii. sensory innervation: Trigeminal (CN V ) 1 iii. parasymp. innervation: pteryogoid ganglion of facial nerve (secretomotor) iv. Path of tear drainage: o lacrimal gland  canals  conjunctival sac on surface of eyeball  surface of eye  lacrimal puncta (in papillae)  canalicula lacrimal sac  nasolacrimal duct d. Conjunctiva: mucosa that covers eyelid and goes onto sclera of eye i. rich with blood vessels; gets inflamed (drinking or irritation) e. Eyelids: protective skin flaps i. Muscles 1. levator palpebrae superioris o Motor Innervation: CN III o Fxn: opening superior tarsus o assisted by superior tarsal muscle 2. Orbicularis Oculi a. Motor Innervation: CN VII b. Fxn: Blinking and tightly closing eye ii. Tarsus (superior and inferior) with tarsal glands (mybomium glands) 1. Glands open up on inner surface of eyelid 2. Secrete lipid => prevents eyelids from sticking together 3. Under hormonal control: sebaceous gland 4. Duct can get clogged  cyst iii. Ciliary glands associated with eyelashes (cilia): superficial 1. When clogstye 1 II. The Eyeball a. Layers i. Fibrous outer coat 1. sclera: tough, dense fibrous coat that covers post. 5/6 of eyeball 2. cornea: continuous with sclera, transparent ii. Vascular middle coat—three components are continuous 1. Choroid: highly vascularzied layer supplying blood and nutrients to eye; most richly vascularized structure in body 2. Ciliary body: donut shaped structure surrounding lens a. Zonular fibers: connect lens sheath to ciliary body b. Contraction=>lens flattens c. Relaxation=> lens rounds up 3. Ciliary processes: produce aqueous humor (in posterior chamber) a. Anterior chamber: from cornea to iris b. Posterior chamber: from back of iris to ant. surf. of lens o humor flows from posterior to anterior chamber thru pupil o nourishes and bathes cornea and lens (avascular) o Aqueous humor drains into canals of Schlemm o fluid is replenished every 90 minutes 4. Iris: surrounds pupil (hole=aperture of camera) a. Fxn: controls amount of light entering eye by changing shape and size of pupil b. CN III—parasympathetic innervation (contraction) i. goes thru ciliary ganglion ii. dependent on circular, concentric fibers c. Sympathetic nn.— dialation (long ciliary nerves) i. dependent on radial fibers iii. Neural inner coat: retina—posterior 5/6 of eye 1. Two different layers: developed separately a. Pigmented layer: fused with choroid b. Neural layer: picks up light rays i. axons of ganglion cells travel towards optic disk ii. connect to bipolar cells rods and cones c. Optic Disc: entry of optic nerve into retina i. In middle => no photoreceptors (blind spot) ii. Central artery/vein of retina travel with optic N. iii. Optic nerve covered by all
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