Dissection notes - Eye #1

Upon dissection this eye had been immersed in coconut oil and brought to about 50F for a day. My objective was to examine the eye from the rear after quartering the retina into four quadrants and laying the flaps back to expose the interior. I used a standard scalpel with a #21 blade.

Prior to the incisions, the eyeball was still quite firm. There was no cloudiness in any portion of the interior. I laid back the flaps exposing the vitreous humour. I was holding the eyeball in a cutaway ping pong ball so that it would hold its' shape when the cuts were made. This worked very nicely.

The vitreous humour, the lens, and the aqueous humour were still quite crystal clear. However, there was a bit of leakage of black pigment smearing into the vitreous humour from the interior surface of the eyeball adjacent to the cuts I had made. I had not noticed this pigment in the eyes of other animals. Interesting, but not enough so that I was going to be distracted for long from the lens, my central interest.

I swabbed these darkenings away with some cotton swabs, trying not to disturb the integrity of the rest of the vitreous humour. It was about of the consistency of the stiffer portion of the white of a very fresh chicken egg. I lifted the eye out of the ping pong ball and examined the image that came through. It was not appreciably out of focus and would have probably cleared up entirely if I had smoothed the surface of the exposed vitreous humour with a microscope slide cover and then laid it on the surface, but I didn't have one handy.

Most of the structures of the eye are tougher and more durable than you would guess. Eventually I removed a large portion of the vitreous humor with a plastic spoon. It really held its' form pretty well, but probing and prodding caused some liquefaction due to the mechanical breakdown of some of the invisible microfibers within. I had expected the capsular membrane to be tougher than it was.

I was particularly interested in observing the interface between the zonules and the membrane of the lens capsule. No such luck. The membrane had apparently spontaneously ruptured. I did not think that I had done anything severe enough to cause that during the dissection. I can only guess that it must have occurred during the time that I was removing the eye from the skull, or at the rather traumatic moment of the death of the buck.

I was a bit disappointed about the membrane, but my central interest was the lens. In its' totally relaxed state, it was quite globular, slightly flatter on the posterior face, much thicker in cross section than one would imagine. It was closer to marble shaped than lens shaped. Clearly, without the influence of the zonules and capsular membrane, the lens was not really what we usually think of as lens shaped. I put it aside, immersed in some tepid coconut oil. I wanted to play with the iris, which was quite durable and resilient.

I should mention that the pupil opening is very round, but the periphery of the iris is oval. This is why you see no white of the eye even when the deer's eye is wide open.

The next thing I wanted to do was to try to drill a hole in the lens using a conventional drillbit (1/16") by hand. It went through the lens nicely but when I removed the drill, the hole filled in. Mechanically drilling a hole in a gel was a long-shot, but I still needed to give it a try. I then did some other destructive testing of the lens until there was little left to play with.

That's about it. I decided to think a while before doing the other eye. No sense in repeating the same procedures. Not much learning in that. More later.