How does the eye function? Very simply the eye works like a colour video camera. The iris (the coloured part) acts as the aperture of the camera to regulate the amount of light reaching the inside of the eye. The cornea, together with the lens of the eye, bends the light rays and brings them to a point of focus on the retina. The retina acts like a photographic film and transmits images to the brain via the optic nerve.

These three conditions are referred to as refractive errors. All three involve distortions in the shape and length of the eye, which effects refraction, or the bending of light as it is focused on the eye's retina. All three conditions can be treated separately or in combination. Most refractive errors can be treated within a defined range of optical power.

The major symptoms of refractive errors are blurred vision, eyestrain and possibly ghosted images. These symptoms usually disappear with either corrective lenses or one of the various forms of eye surgery.