Perfect Vision
Perfect (20/20) vision occurs when the rays of light entering a spherical cornea focus precisely on the surface of the retina -producing a sharp image. No corrective lenses, such as glasses or contact lenses, are required.
Nearsightedness
Nearsightedness, or myopia, occurs when the curvature of the cornea is too steep or too long. This steep curvature or elongation of the eye causes the rays of light to focus in front of the retina. As a result, nearby objects can be seen clearly but distant objects are blurry.
Farsightedness
Farsightedness, or hyperopia, occurs when the cornea is too flat or short. This flatness or shortness causes light rays to focus behind the retina rather than directly onto the retina. As a result, distant objects can be seen clearly but nearby objects are blurry.
Astigmatism
Astigmatism can exist alone or in combination with nearsightedness or farsightedness. An abnormal, non-spherical (football) shape of the cornea causes light rays to focus at more than one point. The result is a distorted or blurred image.
