Eyeball Dissection Observations
Materials:
*sheep eyeball *dissection tray *safety goggles
*scissors *paper towels *probe
*gloves (optional)
Procedures:
External parts of the eye
1. Get an eyeball from the teacher and place it on the tray so that the front of the eye is facing you. Rotate the eye until the tear gland is facing you.
2. On the outside of the eye, find each part of the eye listed below. On Eye Drawing #1, Label, color and write the function of each part of the eye that you find using Diagram #1 to help you.
a. Fat- large amounts of fat help to protect & cushion the eye from shock
b. Tear gland- forms a bulge at the top area of the eye. Produces tears to wash the surface of the eye.
c. Tear ducts- tubes that carry tears from the gland to the eye
d. White coat- Tough outer coat of the eye (white of the eye)
e. Iris- round black circular section that controls amount of light entering into the eye
f. Pupil- Round hole at the end of the iris. This is where light enters into the eye.
g. Eye muscles- Reddish flat muscles around the eye.
i. Upper muscle- muscle on top of the eye that raises the eye
ii. Lower muscle- muscle below the eye to lower the eye
iii. Outer muscle- muscle on the outside that moves eye away from the nose
iv. Inner muscle- muscle that moves the eye toward the nose
3. Cut away the muscles using your scalpel. Be careful when using the scalpel. Do NOT cut towards your body or someone else’s body.
4. Turn the eye so it is facing sideways, to the right/left of you. Look at the front surface of the eye. Find the parts below. Label, color and write the function of each part that you see in Eye Drawing #2, use Diagram #2 to help. (The optic nerve you may have to draw into the diagram #2 picture. Do NOT color in the muscles.)
a. Optic nerve- Found in the back. The optic nerve is a white cord connects the eye to the brain.
b. Eyelid- Covers and protects the eye from dust, bright light, impact
c. White coat- Tough outer coat of the eye (white of the eye)
d. Membrane- Smooth moist membrane that covers the white coat
e. Cornea- Clear layer in front of the eye that allows light to enter & helps focus light
f. Iris- round black circular section that controls amount of light entering into the eye
g. Pupil- Round hole at the end of the iris. This is where light enters into the eye. Changes in the pupil are caused by changes in the iris.
i. When bright light is present, the iris closes/ constricts the pupil.
ii. When there’s very little light, the iris opens/ enlargens the pupil.
Internal Parts of the Eye
1. Place the eye on the tray so that it is facing you.
2. Call the teacher over to pierce the white coat behind the edge of the cornea with a scalpel. Make sure the hole is large enough for your scissors.
3. Use your scissors and carefully cut around the eye using the edge of the cornea as a guide. Lift the eye and turn it as needed as you cut. Try not to squeeze the liquid out of the eye and be careful.
4. Remove the front part of the eye. Place the back part onto your tray with the inner part facing upward (so you don’t lose the liquid).
5. Locate the following parts of the eye. Label, color and write the function of each part that you find on Eye Diagram #3 using Diagram #3 to help you locate the parts.
a. Cornea- Feel the tough tissue of the cornea.
i. Use your scissors to cut across the cornea to see how thick it is. Measure and record the thickness in centimeters of the cornea under Diagram #3.
b. Vitreous humor- liquid that fills the eye and gives it shape
c. Iris- black tissue that controls amount of light entering eye
d. Pupil- Round hole at the end of the iris. This is where light enters into the eye.
e. White coat- Tough outer coat of the eye (white of the eye)
f. Lens- The lens is seen through the pupil.
g. Retina- The white tissue inside the back of the eye is the retina.
i. Try to find the blood vessels that are inside the retina. Label and color the retina and blood vessels in Eye Diagram #4.
6. Use the probe to lift up and remove the lens. The lens is normally clear but may be cloudy due to being preserved.
a. If you can see through the lens, try to read print to observe the magnification power of the lens.
7. Using your scissors, cut across the lens to observe the layers of tissue that form the lens. Peel off several layers of the tissue and note the fine fibers.
8. Write down your observations about the lens underneath Eye Diagram #3.
9. Dump out the vitreous humor onto the tray to observe the retina below.
10. Lift out the retina. Find the dark colored layer known as the dark coat that is attached to the white coat. Many animals have a shiny layer that reflects light into the eye to better their night vision. Human dark coat does not have a shiny layer.
11. Underneath Eye Diagram #4, write down if sheep have a shiny dark coat or not.
12. Throw away the parts of the eye in the designated container.
13. Clean and dry all dissection tools and the tray and place them back where you found them.