Analyze and experience, through dissection, the structure of a cow’s eye.
Experiment and Observations:
We started by cutting the excess fat and muscle around the eye. This tissue was a bit tough to cut through, requiring a sharp scalpel and sharp scissors. This seems fairly obvious. The muscles around the eye are required to move the eye around so that the cow can focus on objects without moving its head. Humans would have a similar structure.
After just a few minutes of cutting the optic nerve became visible and prevalent. It was a very tough stem-like structure that extends out the back of the eye. This is the nerve that sends the images received by the eye to the brain for interpretation.
Once the fat was cut away the cornea (outer covering) and the sclera became visible. These are the outer coverings of the eye and are, not surprisingly, difficult to cut through since they protect the sensitive inner eye.
We cut the eye in half around its circumference and immediately noticed the vitreous humor. This gel substance sits inside the eye and protects/holds the inside structures of the eye. This fluid was probably about 30 - 35 ml and acts as the “filler” for the space in the eye.
Next we decided to remove the iris. This was about 2 inches across with an opening in the center where the light and images pass through into the lens (pupil). The iris in the cow is brown, hence the cow’s brown eyes when looked at in the daylight. The iris is the muscle that regulates the amount of light that enters the eye so that it is easier to focus in light/dark conditions.
Next we removed the lens. This was about the size of a small marble (one inch across) and once we cut into it, the lens started to “shed” layers as we pulled them off. This must be some sort of magnification technique or just the way the lens is built. Perhaps the layers help to clarify what we see as well.
Behind the lens lies the retina - the area that collects the images and sends them to the optic nerve. We can see the nerves in the back that branch out from one point, which leads to the optic nerve. The retina is basically attached to the eye at this point as well.
Once we removed the retina, we got to the tapetum, which was the most interesting part of the experiment. The tapetum is the blue-green colored substance at the back of the eye that reflects light. It is the same substance you see when a cat’s eye glows green in light, except a cow’s eye would be blue-green. Humans do not have this substance in their eye.
After dissecting the eye I realized how important it would have been to dissect and learn about the eye for someone like Goethe or Newton to make the observations that they did. We can learn so much about the structures of the eye through dissection that can help us get closer to our understanding of color and how the brain interprets color and sight.