Before we talk about what can go wrong, it is important to understand how the eye functions with it is working properly. The eye is like a camera. When you take a picture, the lens in the front of the camera allows light through and focuses that light on the film that covers the back insisde wall of the camera. When the light hits the film, a picture is taken. The eye works in much the same way. The front parts of the eye (the cornea, pupil, and lens) are clear and allow light to pass through. The light also passes through the large space in the center of the eye called the vitreous cavity. The vitreous cavity is filled with a clear, jelly-like substance called the vitreous or vitreous gel. The light is focused by the cornea and the lens onto a thin layer of tissue called the retina, which covers the back inside wall of the eye. The retina is like the film in a camera. It is the seeing tissue of the eye. When the focused light hits the retina, a picure is taken. Messages about this picture are sent to the brain through the optic nerve. The brain then interprets these messages and this is how we see.