lab 15 sheepeyediss
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College Level Sheep Eye Dissection Guide
Passaic County Community CollegeDesign - Dr. E. Hager
Edited by Dr. S.C. Wache
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Note the eyelid on the anterior half of the eyeball.
Note the fat around the eyeball. It protects by cushioning the eyeball within the bones that surround the eye
Take the fine tipped scissors to cut away the eyelid and extra fat.
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Scalpel
Cleaned Eyeball
Excess Fat and Eyelid
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Cornea
–extension of sclera over the lens
-opaque in preserved specimen
Anterior View of the Sheep Eye
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Cornea
Pupil
Sclera
Anterior View of the Sheep Eye
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Optic Nerve
–cranial nerve II
Posterior View of the Sheep Eye
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Prepare a coronal cut: Start by making a primary incision into the sclera using a scalpel; then, using the bone cutting scissors, complete the coronal sectioning of the eyeball.
Optic Nerve
Incision into the tough connective tissue called the sclera
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Sensory Cranial Nerve II
Sclera
Lens in the anterior half
Vitreous Humor in the posterior half of the eyeball: this jelly-like fluid helps maintain shape of the eyeball
Function of the lens: it bends the parallel waves of light; it aids in focusing of light. Read TB, p. 457, Clin. Appl. 12.5 regarding myopia and hyperopia.
Note the thickness of the sclera layer.
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Anterior Half of the Sheep Eye
Lens
Ciliary Body
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The lens is easily pushed out.
Often, some of the vitreous humor sticks to it.
Removal of the Lens
Lens
Suspensory Ligaments / Ciliary
Muscles sticking to the lens
Vitreous Humor
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Lens removed
LensCiliary Muscles
Iris
Pupil
Compare to Lab Manual Fig. 35.9.
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Lens
Vitreous Humor
Suspensory ligaments attach the ciliary muscles to the lens.
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Posterior Half of the Sheep Eye
Nervous tissue overlying the retina.
Ganglionic nerve directed toward the optic disk.
Choroid coat in-between the retina and the sclera.
Sclera
Optic disk: place where the ganglia join to form the optic nerve and where there is no retina (also called the ‘blind spot’)
Note: The choroid coat contains melanin (otherwise found in the melanocytes within the basal layer of the skin) which protects the inside of the eye from light and prevents light from entering from the sides.The retina is a light sensitive area rich in the two photoreceptor cells, rods and cones.
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Sclera
Tapetum lucidum- shiny part of the choroid coat.
Melanin containing part of the choroid coat.
Retina and nervous tissue pulled to the side. Note: The fovea centralis (a small rodless area of the retina that affords acute vision) and the macula lutea constitute the region of maximum visual acuity and are made up almost completely of cones which provide color vision. Rods are active during night vision.
Note: The choroid coat also contains the tapetum lucidum which reflects light and enhances night vision. It is well developed in cats. Rhodopsin, a protein within rods and cones, is excited by photons, the energy-rich particles that make up a light wave. Once excited above threshold, an impulse is sent along the sensory nerve to the CNS where it is interpreted in interneurons.