The structures of the eye include:

• The pupil, which is the opening in the colored part of the eye (iris). The iris controls the size of the pupil in response to light outside the eye so that the proper amount of light is let into the eye.
• The lens, which is located behind the iris and is normally clear. Light passes through the pupil to the lens. Small muscles attached to the lens can change its shape. Tightening or relaxing these muscles causes the lens to change shape, allowing the eyes to focus on near or far objects.
• Vitreous gel (also called vitreous humor), which is a thick liquid that fills the eye. It helps the eyeball maintain its shape.
• The retina, which is a thin nerve membrane that detects light entering the eye. Nerve cells in the retina send signals of what the eye sees along the optic nerve to the brain.
• The optic nerve, which is the nerve at the back of the eye that carries visual information from the eye to the brain.
• The macula, which is near the center of the retina at the back of the eyeball. The macula provides the sharp, detailed, central vision a person uses for focusing on what is directly in the line of sight.

By	Healthwise Staff
Primary Medical Reviewer	Kathleen Romito, MD - Family Medicine
Specialist Medical Reviewer	Christopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology
Last Revised	January 20, 2011