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As light enters the eye, it strikes receptor cells on the retina called rods and cones. The light triggers a chemical reaction in the cells, which then send electric impulses through the optic nerve to the brain.

Review Date 9/7/2021

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, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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