The human eye has been referred to as the most complex organ in our body. When you consider how difficult the task of providing vision is and how something so small can have so many working parts. The human eye is similar to a camera in its function. A tough white covering called the sclera protects the eye. Part of the white sclera can be seen in the front of the eye. A clear delicate membrane called the conjunctiva covers the sclera.The first part of the eye's visual system is the clear round membrane at the front of the globe called the cornea, similar to the lens of the camera. Behind the cornea is a colored circle of tissue called the iris. The iris controls the amount of light that enters the eye by enlarging or reducing the size of the opening in its center, called the pupil. Behind the iris is the lens, the second part of the optical focusing system of the eye. The large space behind the crystalline lens is filled with a clear jellylike substance called the vitreous. The vitreous is transparent allowing light rays to pass through unaffected to produce an image on the back surface of the eye, commonly referred to as the retina. The retina has a series of light sensitive cells which acts like the film of a camera reacting to the incoming light and sending a record of it via the optic nerve to the brain.