Sheep Eye Dissection

I learned from sheep eye dissection was the stump of the optic nerve to the left, and the cornea to the right . The sclera is the tough, outer coat of the eyeball, which helps keep the shape of the eye,and protect it from injury.The pinkish parts around the sclera are the remnants of extrinsic muscles, which have been cut off. These muscles move the eyeball in its socket from left to right, up and down , and a little bit of rotation. The back of the eyeball, seen from inside, shows the retina as a translucent greenish membrane, with wrinkles in it. Although some of the wrinkles formed from taking the eye apart, many of them are the remains of blood vessels, which supply the retina with nutrients and oxygen.
The point where all these blood vessels, and also all the nerves of the retina, gather together to leave the eye and become the optic nerve, is the blind spot. There is no room for any light receptors in the blind spot, because of all the nerves and blood vessels here.
A tiny bit of black choroid is exposed at the bottom of the eyeball. The rest of the choroid can only be seen through the veil of the retina.
The black part of the choroid blocks and absorbs light, preventing light from bouncing around in the eye, and washing out the image. It also prevents bright light from coming through the sclera from outside.
Because sheep have to watch out for predators, such as wolves, which might attack when it is getting dark, they have a band of very reflective choroid, called the tapetum lucidum, across the middle of the eyeball, from left to right. The tapetum makes the retina in front of it twice is sensitive to light, by bouncing back light rays which may have missed a light-sensitive cell, and giving them a second chance to be picked up. Behind the retina here, the tape tum lucidum may be silvery, pearly white, or a beautiful iridescent blue when exposed.
The blind spot is not visible, but its approximate position can be guessed at by following the direction of the optic nerve.
The blind spot is never located over the tape tum, as this is the zone where sensitive vision is needed for sheep to see danger coming. Humans do not have a tape tum. Instead, in the human eye, a small central area in each eye, called the fovea, is packed with colour-sensitive cells called cones. This gives us sharp, full-colour vision in the centre of our visual field. Sheep do not see colour, and do not have a fovea.
Sheep do not have a round pupil like humans. Instead of varying from a small circular opening in bright light, to a large circular opening in dim light, the sheep's pupil remains wide, and only varies in height. In bright light, the pupil may have a peanut-like shape. As the light becomes dimmer, the sheep's pupil will chance to an oval shape, then finally to a full circle. This gives the sheep wide-angle vision, to scan the horizon for predators without moving its head.
The iris is made of muscles, which change the size (and shape, in sheep) of the pupil. Pigment such as melanin in the iris prevents light from entering the eye, except through the pupil.The ciliary muscle (or ciliary body) surrounds the edge of the lens, and causes the lens to change in thickness, to focus on near or far-away objects.The lens is clear and transparent as crystal in a living eye, but the preservative changes it to a cloudy orange color, almost opaque to light. In life, it is flexible, and able to change shape to focus. In preserved eyes, it becomes hard and rigid.

en.wikipedia.org/wiki/Eye/
http://retina.anatomy.upenn.edu/~lance/eye/eye.html
http://www.macula.org/anatomy/eyeframe.html