The Sheep Eye Dissection

Yesterday, we completed a sheep dissection in class. The images below represents the different stages of our dissection. The first image shows the cornea, which is the clear layer of proteins covering the main portion of the eye. What is fascinating about the cornea is that these transparent proteins do not require any blood or oxygen as there are no capillaries in the cornea. Also shown in the first image is the sclera, extrinsic muscle, and fatty tissue. The sclera is an EXTREMELY tough (it took a bunch of cuts with our scalpel to finally break through it) which protects and contains the contents of the eye. Onto the next image. As you can see, my partner and I (finally) cut through the sclera. In essence, we opened the eye. On the left half of the eye, we see the jelly-looking substance: the vitreous humor. This jelly helps to maintain the pressure inside of the eye. On the right half, the banana-looking structure is the retina. The retina receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition. The black and iridescent blue film behind the retina is the choroid. This is used to reflect light. The tapetum lucidum, the iridescent blue portion, is used to help nocturnal animals see in the dark. Humans do not have a tapetum lucidum. In the third and final image, the eye is completely take apart. The vitreous humor, the cornea, the choroid, the tapetum lucidum, and the sclera are visible. Three new pieces are the lens, which is to the right of the vitreous humor and to the left of the cornea, and the pupil and iris, which is between the upturned half of the eye (with the choroid) and the cornea. The iris is the brownish region in the sclera. The pupil is the opening inside the iris. The whole job of the iris and pupil is to control the amount of light that gets into the eye. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina.

An untouched sheep's eye

A sheep's eye with the back part removed.

From left to right: vitreous humor, lens, cornea, front of eye,
and back of eye