netbook
desktop
mobile
tablet-landscape
tablet
phone-landscape
phone
Research to Prevent Blindness

How the Eye Works

View Video

Light rays enter the eye through a transparent layer of tissue, known as the cornea. The cornea bends light through a watery substance called the aqueous humor. As light continues on its pathway it passes through the dark, round opening in the center of the colored iris known as the pupil. The iris, the part of the eye that gives the eye its color, also changes the size of the pupil from very small to large in order to regulate the amount of light that is entering.

Light then passes through another structure, called the lens.  The lens is attached to muscles which contract or relax in order to make adjustments which allows light to be focused for clarity. Once through the pupil and lens, light then passes through the larger posterior portion of the eye that is filled with a clear, jelly-like substance called the vitreous humor. Continuing through, light comes to the retina, the membrane that lines the back wall of the eye, containing photo- receptor (rod and cone) cells. These cells convert light to electrical impulses. 

The cone cells (about 7 million in number) are in greatest concentration in the small, central part of the retina, called the macula. This area is responsible for producing sharp, detail vision and color vision. The rod cells (numbering about 100 million), in the peripheral retina, provide vision in dim light. Electrical impulses are sent through the optic nerve, the bundle of retinal fibers that exits the back of the eye, and transported to the brain where they are interpreted in the primary visual cortex and an image is perceived. 

Order RPB's Guide to Eye Health

The Parts of the Eye

Click the red targets to see definitions for parts of the eye, or move the blue magnifying glass to explore the eye diagram.

 

Diagram courtesy of National Eye Institute, National Institutes of Health.

Search the National Eye Institute's online glossary on the eye 

 

Subscribe

Get our email updates filled with the latest news from our researchers about preventing vision loss, treating eye disease and even restoring sight. Unsubscribe at any time. Under our privacy policy, we'll never share your contact information with a third party.