Definition

Vision disorders are conditions caused by the eye's inability to properly focus light rays. Three major types of vision disorder are hyperopia (pronounced HY-puh-ROH-pee-uh), or farsightedness; myopia (pronounced my-OH-pee-a) or nearsightedness; and astigmatism, which causes the eye to form a blurred image of an object.

Description

Light that strikes the eyeball first passes through the cornea. The cornea is the tough, transparent covering at the front of the eye. It is shaped like a dome, with the top of the dome facing outward. Light then passes through the lens. The lens is located just inside the eyeball, behind the cornea. The lens has a double-convex shape. That is, it bulges outward in the middle.

The cornea and lens bend light as light waves pass through them. This process is known as refraction. In a normal eye, the light waves are brought to focus on the...