OverviewThe cornea allows light to enter the eye. As light passes through the eye the iris changes shape by expanding and letting more light through or constricting and letting less light through to change pupil size. The lens then changes shape to allow the accurate focusing of light on the retina. Light excites photoreceptors that eventually, through a chemical process, transmit nerve signals through the optic nerve to the brain. The brain processes these nerve impulses into sight.
Update Date 9/2/2014
Updated by: Franklin W. Lusby, MD, ophthalmologist, Lusby Vision Institute, La Jolla, CA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.