Cow's Eye Dissection

image source: Daily Mail

When I caught word that we would be completing a cow's eye dissection, my mind immediately flashed back to 5^th grade, when I did the exact same experiment for the first time. Although cow's eyes haven't changed all that much since 1999, I've certainly come a long way since then, and therefore observed much more than just “there is a lens, an iris, and some squishy stuff in the middle.”

Fat and Muscle – In fifth grade, the fat and muscle had already been trimmed away for us, as no one in their right mind would trust a fifth grader to complete that task safely or successfully, so this step was entirely new for me. The fat was apparent, but I had a hard time determining whether I should cut what ended up being the muscle, because it was wrapped so perfectly around the eye. I ended up realizing that it should in fact be cut away, and after doing so, I was left with a very apparent sclera.

Sclera – The sclera was a much harder shell than I had expected (If I dissect again, I will be less careful cutting off the fat/muscle than I was this time). After the initial incision was made and the first bit of vitreous humor made its escape, the rest of the cut went smoothly.

Vitreous Humor – The vitreous humor just felt like 'jelly water' and fell out of the eye with little effort. This is probably what I remember the most from the fifth grade dissection, and also what I observed the least about in this dissection.

Lens – The lens proved to be the most interesting part for me this dissection. Although it is one of the parts I remember from fifth grade, I did not remember it being so hard/cloudy. Maybe I did, but just was not aware at the time that due to its function, it's much softer/clearer when the cow is alive. As a whole, the lens was about 2 cm in diameter, and 1 cm high. The lens could actually be peeled, and had the consistency of “string cheese and an onion” as said by Ben. The string cheese effect became less and less apparent the closer I peeled to the middle of the lens.

Iris – The iris was a very thin, almost paper-like muscle. I was surprised how easy it was to peel away from the sclera. The Iris was about 3 cm in diameter, and the side facing outward was brown, which I learned was simply because cows have brown eyes. :)

Retina – I was also surprised about how easy it was, for the most part, to detach the retina from the eye (up until the optic nerve, of course). The retina had a very similar consistency/color as the iris, only the edges of the retina weren't quite as distinct as they were on the iris. The edge of the retina was more brittle and arbitrary as to where it would easily peel off and where it would decide to stick.

Tapetum – Actually, I found this part to be the most interesting part of the dissection, as I did not even know that this part of the eye existed before I began the dissection. The tapetum was a brilliant looking layer that apparently allows for better night vision in cows, cats, and I assume other animals. It looked like a dark blue, light blue, and purple gas spill on water. I had just assumed that this was the back of the sclera, until I realized that this part could be peeled off as well. After realizing that the tapetum was its own part, I was surprised that the tapetum and the retina did not stick together as I peeled off the retina.