The eye has many parts to it that make it function right and without any of them we would not be able to see right or even see at all. Some parts of the eye are the the iris which is a muscle that makes the pupil bigger to let more light into the eye and make it smaller to let not as much light in. 

The clear jelly that gives the shape of your eyeball is called the vitreous humorous, it needs to be clear because if it was not then you would be blind because the light that the pupil would let in would not get through to the retina.