Q. How does my eye work? A. The primary function of your eye is to focus light.  You need glasses or contact lenses when your eyes cannot focus light properly. Your eye works like a camera.  Light rays enter through the cornea, which provides most of the focusing power.  Light then travels through the lens where it's fine-tuned to focus properly on the retina on the back of the eye. The retina acts like film in the camera.  Light is changed by the retina into electrical impulses that are carried by the optic nerve to the brain.  Light must be focused precisely on the retina for you to see clearly. A brief description of the various parts of the eye follows.  This will help you better understand the terminology and process behind different vision correction procedures.

A Glossary of Terms 

Cornea  The cornea is sometimes referred to as the "window of the eye".  It provides most of the focusing power when light enters the eye.  The cornea is composed of five layers of tissue.  The outer layer (the epithelium) is the eye's protective layer.  

Pupil  The pupil is the "black circle" in your eye.  The primary function of the pupil is to control the amount of light entering your eye.  When you are in a bright environment, the pupil becomes smaller to allow less light to pass through.  When it is dark, the pupil expands to allow more light to reach the back of your eye. 

Lens  The lens is the clear structure located behind the pupil.  Its primary function is to provide fine-tuning for focusing and reading, which it accomplishes by altering its shape.  At the age of 40 to 50, the lens becomes increasingly rigid and presbyopia sets in, usually making reading glasses necessary.  As you age beyond 60, the lens becomes progressively cloudy and hard.  Cataracts may form and this clouding may eventually interfere with your vision.

Iris  The iris is the colored part of your eye.

Retina  The retina consists of fine nerve tissue that lines the inside wall of the eye and acts like the film in a camera.  Its primary function is to capture and transmit images.

Optic Nerve  The optic nerve carries images to the brain.

Sclera  This is the "white part" of your eye.  The sclera's purpose is to provide structure, strength, and protection for your eye.  

Vitreous Gel  This is the clear "gel-like" substance located inside the eye's cavity.  It provides the spherical shape to your eye.