- (AKA
myopia) If you are nearsighted you have blurred distance vision, however near vision remeains sharp, except in some cases. In most cases, the eyeball is too long from front to back. As a result, light rays from distant objects meet before they reach the retina When the light rays do strike the retina, they form a blurred image. Eyeglasses or contact lenses that are concave bring the light rays together at the retina and correct most cases of nearsightedness. Concave lenses are thinner in the middle than at the edges.
- (AKA
hypeopia) This occurs in most cases because the eyeball is too short from front to back. Unless the lens accommodates, light rays from distant objects reach the retina before they meet, causing a blurred image. The lens of a normal eye remains relatively flat for distance vision and becomes thicker for nearby objects to be brought into focus. In a farsighted eye the lens mus also thicken for sharp distance vision. Sharp images of distant objects are received by far sighted eyes. But the constant use of the muscles of the ciliary body to adjust the shape of the lens may cause headaches and eyestrain. The lens may not thicken enough for sharp near vision also. Glasses or contacts that are convex correct farsightedness. Convex lenses are thicker in the middle than at the edges.
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