Friday, February 11, 2011

Cow Eye Dissection

For the cow eye dissection we began by cutting off the muscle and fat from around the eye. We started this process with a scalpel, but quickly found that the fat and muscle were difficult to cut through, so we switched over to scissors. The fat/muscle was white, light pink and tan. It was somewhat stretchy and squishy.

The net cut was around the center of the eyeball to reveal the humour in the center. This humour was opaque and grayish. The texture was similar to that of lumpy jelly. The lumps and the slight gray tinge lead me to believe that this cow was either very old when killed, had poor eyesight or the eyeball was at some point contaminated. The humour should have been transparent to allow light to pass through. This is also true of the lens. After the humour was removed we could easily see the lens attached to the front half of the opened eyeball. The lens was hard, pinkish and cloudy and approximately 18 mm by 12 mm. The lens should have been a clear, magnifying oval. We found that it was easy to peel layers off of the surface of the lens. The texture of these layers was a cross between that of string cheese and an onion. Thin layers peeled back to reveal a harder ball at the center of the lens.

We next turned our attention to the iris. The side of the iris that normally faces out was a dark brown color while the inside was a much darker brown/black. In the center of the iris was the pupil. The pupil measured 7 mm by 12 mm across. Opposite the iris, on the back of the eye, was another interestingly colored layer. The back of the eye was a blue/green color and quite shiny. Near the bottom center of the blue/green the retina was visible. The retina was approximately 4 mm in diameter. Following the retina through the back of the eye we found the optic nerve protruding from the back surface. The optic nerve was cream colored and was surrounded by brownish muscle tissue. When the retina was removed we could easily see a connection between the back of the inside surface of the eye and the optic nerve.

In our final exploration we looked at the cornea. The cornea was about 2 mm thick, whereas the surrounding tissue was a bit thicker at 2.5 mm. The cornea was also softer than the surrounding tissue, with a slightly stretchy, rubbery feel. When pressed on with a scalpel the cornea made small crunching noises.

Overall our eye was pretty much the same as the one described in the educational video that we watched pre-dissection, although our aqueous humour and lens were slightly less clear. We also found that the retina on our eye was much more fragile than the one in the video and, unfortunately, we ended up cutting ours before getting an accurate measurement of its length.

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