The eye is often compared to a camera, with its light-sensitive retina taking the place of the photographic film and the pupil representing the aperture (or opening) in the diaphragm, which covers the lens. However, this analogy doesn’t do justice to the remarkable properties of the human eye. All the parts of the eye that light passes through—the cornea, lens, vitreous, and retina—are made of living tissue and yet maintain their transparency. And the range of light and color intensities that can be perceived by the human eye is much greater than that of any man-made film.

Another eye diagram is provided by the National Eye Institute of the National Institutes of Health.

A glossary of eye-related terms is provided by the Schepens Eye Research Institute; this should be useful for understanding the structure and function of the eye’s component parts. The glossary also defines terms you may hear from your eye doctor and has links to pages about common eye diseases.

At the front of the eye is the cornea, a clear dome that helps focus light. It and the sclera, the white of the eye, protect the interior of the eye. The surface of the eye is protected and lubricated by the eyelids. Behind the cornea is the lens (crystalline lens), which completes the focusing of light onto the retina at the back of the eye. The retina contains nerve cells that send signals, through the optic nerve, to the brain.

Any part of the eye can be damaged through structural defect, disease, injury, or age-related changes. Two very common defects are poor focusing of light (refractive error, correctable by eyeglasses) and loss of transparency of the lens (cataract, treated by a standard surgery).

Click here to learn more about when to seek help from an eye care professional.