The retina is a light-sensitive layer at the back of the eye that covers about 65 percent of its interior surface. Photosensitive cells called rods and cones in the retina convert incident light energy into signals that are carried to the brain by the optic nerve. Retinal photos allow your doctor to evaluate your retina the day of your exam and furthermore document its appearance for comparison at subsequent exams. This is very important to maintaining good vision for life.