vision

Ability or act of seeing. Light that enters the eye is focused by the eye lens, creating a sharp image on the retina. Electrical signals from the retina travel down the optic nerve where they are interpreted by the brain.

In humans, the image of an object created by each of our eyes is slightly different because our eyes are in different positions. The brain combines the two images to give a sense of depth. This is known as binocular vision. With one eye closed we lose some of our sense of depth and perspective.

A person who is short-sighted (suffers from myopia) can see clearly objects that are close, but cannot create a sharp image of objects that are far away. The light from distant objects is being focused in front of the retina. This defect can be correct using diverging lenses.

A person who is long-sighted (suffers from hypermetropia) can see clearly objects that are far away, but cannot create sharp images of objects that are close. The light from these near objects is focused behind the retina. This defect can be corrected using converging lenses.