The human eye has three layers. The outermost layer is called sclera. The middle layer of the eye is called the uvea, and the innermost layer is called the retina. The retina is the light-sensitive membrane at the back of the eye. When light enters the eye, the cornea and lens focus the light onto the retina. The central area of the retina, called the macula, contains millions of nerve endings packed closely together. These nerve endings are responsible for the sharpness of the visual image. The retina converts the image into electrical impulses that are carried to the brain by the optic nerve. So, without the retina, the eye cannot communicate with the brain and vision is lost.