Sheep Eye Dissection Procedure

Materials

Sheep eye Latex/vinyl gloves Safety glasses
Lab Apron Dissecting probe Dissecting scissors
Tweezers Dissecting tray Paper towels

Procedure
1. Examine the outside of the eye. See how many parts of the eye you can identify. You should be able to find the whites (or sclera), the tough, outer covering of the eyeball. You should also be able to identify the fat and muscle surrounding the eye. You should be able to find the covering over the front of the eye (the cornea). When the cow was alive, the cornea was clear. In your sheep’s eye, the cornea may be cloudy. You may be able to look through the cornea and see the iris, the colored part of the eye, and the pupil, the dark oval in the middle of the iris.

2. Cut away the fat and muscle.

3. Use the scalpel to make an incision through the sclera in the middle of the eye.

4. Use your scissors to cut around the middle of the eye, cutting the eye in half. You’ll end up with two halves. On the front half will be the cornea. The cornea is made of pretty tough stuff—it helps protect your eye. It also helps you see by bending the light that comes into your eye. Once you have removed the cornea, place it on the board (or cutting surface).

5. The back of the eye is filled with a clear jelly. That’s the vitreous humor, a mixture of protein and water. It’s clear so light can pass through it. It also helps the eyeball main­tain its shape.
6. Now you want to remove the lens. It’s a clear lump about the size and shape of a squashed marble. The lens of the cow’s eye feels soft on the outside and hard in the middle. Hold the lens up and look through it. What do you see? Put the lens down on a newspaper and look through it at the words on the page. What do you see?
7. The next step is to pull out the iris. The iris is between the cornea and the lens. It may be stuck to the cornea or it may have stayed with the back of the eye. Find the iris and pull or cut it out. It should come out in one piece. You can see that there’s a hole in the center of the iris. That’s the pupil, the hole that lets light into the eye. The iris contracts or expands to change the size of the pupil. In dim light, the pupil opens wide to let light in. In bright light, the pupil shuts down to block light out.
8. On the inside of the back half of the eyeball, you can see some blood vessels that are part of a thin fleshy film. That film is the retina. Before you cut the eye open, the vitreous humor pushed against the retina so that it lay flat on the back of the eye.
9. Use your finger to push the retina around. The retina is attached to the back of the eye at just one spot. Can you find that spot? That’s the place where nerves from all the cells in the retina come together. All these nerves go out the back of the eye, forming the optic nerve, the bundle of nerves that carries messages from the eye to the brain.
10. Under the retina, the back of the eye is covered with shiny, blue-green stuff. This is the tapetum. It reflects light from the back of the eye. Have you ever seen a cat’s eyes shining in the headlights of a car? Cats, like sheep, have a tapetum.
Clean-up
Place all biological parts of the eye in the biological waste bucket.
Return the tray and tools to the sink and wash them thoroughly, placing tools in the appropriate places
One person must use paper towel and disinfectant to clean up desks and the surrounding area
Place gloves in the garbage
WASH HANDS CAREFULLY