As light enters the eye, it strikes the receptor cells of the retina called the rods and cones. A chemical reaction results in the formation of electric impulses, which then travel to the brain through the optic nerve.
Update Date 4/18/2013
Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.