Sheep Eye Dissection

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Sheep Eye Dissection
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External Anatomy
Using your scissors, remove all the fat and
muscle tissue surrounding the eyeball. Look at
the before and after pictures below.
before removing fat and muscle
after removing fat and muscle
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Once you have removed all the fat and
muscle surrounding the sheep eye, identify the
structures in the picture below.
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The sclera is the white, outer covering of
the eye. The cornea is the transparent layer at
the front of the eye through which light
first enters the eye. The optic nerve carries
impulses from the eye to the brain.
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Using your scissors, poke a hole in the sclera
just outside of the cornea. Be careful, it may
spray eye juice on you if you squeeze too hard!
poke here with scissors
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Now, insert the point of your scissors into
the hole and cut all the way around the eye
following the line indicated below.
cut all the way around the eye following this line
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Next, remove the portion of the eye
containing the cornea that you just cut out with
the scissors. Now, remove the contents of the eye
and lay them on the tray next to the part you
just cut out. Use the diagram below to identify
the eye struc- ures that are now visible.
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The iris controls how much light enters the
eye by expanding and contracting to control
the size of the pupil. The pupil is the hole in
the iris through which light enters the inner
eye. The ciliary muscle expands and contracts to
change the shape of the lens. The lens
focuses the image onto the back of your eye. The
vitreous body or vitreous humor is a transparent
jelly that fills the inside of the eye.
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Now, look at the empty eyeball and locate
the back layer of the eye called the retina.
Also locate where the optic nerve leaves the
eye. This is called the blind spot.
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The retina is a tissue at the back of the eye
that is sensitive to light energy. This is where
the image is focused by the lens. Light energy
stimulates the cells on the retina which send
impulses to the optic nerve. The optic nerve
carries these impulses to the brain and then you
see. Using your tweezers, remove the retina
which is the white layer covering the back of the
eye. Now you should be able to see a bluish
layer called the tapetum. Look at the diagram on
the next slide to identify the tapetum.
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The tapetum is a reflective surface that
helps some animals to see better at night. If
you have ever seen a dog or cats eyes shine at
night it is from the tapetum. Humans do not have
a tapetum layer in their eyes.
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Cleanup
Throw the eye parts in the garbage, wipe out
your tray with a paper towel, and wipe off the
dissecting tools. Wash your hands with soap and
water and then answer the questions beginning on
the next slide on a separate piece of paper.
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Photograph ID

• Sclera
• Conjunctiva
• Lens
• Iris
• Pupil
• Vitreous humor
• Choroid
• Retina
• Optic nerve
• Eye muscles
• Adipose
• Cornea

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Questions Conslusions
1. What is the sclera? 2. What is the cornea and
what does it do? 3. What is the function of the
optic nerve? 4. What does the iris do? 5. What is
the pupil? 6. What is the function of the ciliary
muscle? 7. What does the lens do? 8. What is the
vitreous humor? 9. Where is the blind spot
located? 10. What is the retina? 11. What is the
function of the tapetum? 12. Do humans have a
tapetum layer?