A Guide for the Dissection of a Sheep's Eye

Put on the gloves. Wash the preservative fluid off the eye by placing it under running water. Dry it with a fresh paper towel.

Locate the parts of the eye: the eyelid, the cornea, the sclera, or "white," the fatty tissue, the optic nerve and the four extrinsic muscle bundles. Note that a human eye has six muscle bundles in the back.

Use the scissors to cut away any excess fat and muscle from the eye, and expose the sclera and the optic nerve. Make sure not to cut the optic nerve, which is a tough, tubelike structure that emerges from the back of the eye. Write down any observations about the eye's appearance. Note that the cornea is cloudy when dead but transparent when alive.

Place the eye in the dissecting pan, with the cornea on your left and the optic nerve on your right. Use your scalpel to make a very small incision through the sclera, halfway between the optic nerve and the cornea. Stop cutting when fluid oozes out of the sclera. Record your observations.

Insert the point of the scissors into the incision, and snip the sclera around the ball of the eye. Roll the eye over as you cut, supporting the eye in the palm of your hand as needed, until the sclera is cut completely in two. Be careful not to cut the lens. Record your observations.

Separate the two halves of the eye, and lay them in the dissecting pan, cut side up. Observe the vitreous humor, which is the clear jellylike substance inside the eye. Observe the dark reflective lining in the back half of the eye -- this is the tapetum, and is not found in a human eye. Observe the saclike structure attached to the optic nerve -- this is the retina, which is responsible for transmitting images to the brain through the optic nerve. Using the probe, lift the retina away from the lining of the eye. Record your observations.

Use your forceps to peel the retina away from the tapetum. Separate the retina from the optic nerve using the scissors or scalpel. Use the forceps or probe to gently separate the tapetum from the outer sclera. Record your observations.

Use your forceps or probe to lift the vitreous humor from the other half of the eye. If desired, tip the eye on its side to spill the liquid out onto the dissecting pan.

Find the lens, and remove it using your forceps. Note that although the lens would be transparent in a living animal, it is cloudy when dead. Observe the suspensory ligament around the edges of the lens. Record your observations.

Examine the rest of the front half of the eye, how the removal of the lens allows light through the pupil. Turn the eye half over, and use a scalpel to make a small incision in the boundary between the cornea and the sclera. Insert the scissors into the incision and cut all the way around the cornea to remove it. Compare the thickness of the cornea with that of the sclera. Record your observations.