Friday, February 11, 2011

Cow Eye Dissection

Touching the cool plastic, running a finger over the cold metal top of the scalpel, finally, after too many long months, my arm felt complete again. Dissections were always the best part of my day in high school; there is a difference between learning from a textbook and actually exploring the images with your own hands. Coincidentally (or maybe not), a similar debate took place in the Bowler and Morus Making Modern Science: A Historical Survey (2005) reading for this week. The two authors discussed the early conflicts between science and medicine: as a doctor, should you have more schooling or more experience? There is a lot that a book with pretty pictures can teach you, but you can learn so much more with experience and discovery. (Maybe this was Faust’s problem, he spent too much time “Entombed within this book-lined tower.../ This is your world! Call this a world!... / Shut out from Nature’s teeming throng, / Which God made man to dwell among, / You skulk in reek and mold alone” (Goethe, Faust, 402-16).) Either way, doctors today get both sides of this debate: working hard for long years in college and then spending long years working with established doctors in hospitals observing and learning. Eye dissections similar to the one we did in class provide experience and thus, are a great learning opportunity.

The eye is a fascinating piece of the body. The eye is a perfect example of one of the main principles of biology: structure goes with function every time. The fat and tissue surrounding the eye, for example, is there to protect the cow’s eye from getting damaged by the scalp (figure one). After removing the fatty tissue surrounding the eye, we carefully inserted the scalpel into the sclera (figure two). After making the incision, we then used scissors to carefully cut the rest of the eye. The sclera was surprisingly tough. As far as structure being for function, this makes perfect sense because the sclera must be tough in order to protect the eye, but it doesn’t appear as thick as it is. Not only that, but the texture is really weird. It is smooth, but moves and feels almost like plastic. After cutting all the way about the eye, we carefully peeled the two halves away from each other, while trying to keep the retina intact on the back half of the eye (figure three). We then had to carefully remove the vitreous humor from the front half of the eye. This was one of the hardest parts of the dissection. The vitreous humor did not enjoy getting poked and prodded to come out (figure four). This part of the eye, which would normally be clear, had a yellowish tint to it. This would be clear in a working eye because you need to be able to see through it. After the removal of the vitreous humor, the lens was easily popped out (figure five). This was probably one of the most fascinating part of the lab. Either it has been too long since I have done this dissection or I have never realized this at all, but the lens is made up of layers and layers of cells. You can peel layers to reach the center. The outer layers of the lens are softer and, as you approach the middle of the lens, it got harder (figure five). The back of the eye came with its own surprises as well. The blind spot was where the optic nerve met the back of the eye. And the behind the retina, there was a beautiful color similar to that of a peacock’s feathers. It is this structure that makes a cow’s eyes reflect back light like a cat’s. Being careful and keep the retina in tact, we found that the retina is attached to the optic nerve (figure seven). This dissection was a lot of fun. The eye is fascinating; full of different structures with their own specific functions which enables us to see everything. However, it is only after dissecting an eye can one really appreciate the anatomy of an eye that provides one with the beautiful gift of sight.

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