Cause Details Myopia (nearsightedness) Distance vision is blurred because light rays are focused in front of fovea. Myopia is usually inherited and often discovered in childhood. Myopia often progresses throughout the teenage years when the body is growing rapidly.
Hyperopia (farsightedness) Near vision is blurred because light rays are focused behind fovea.
It can also be inherited. Children often have hyperopia, which may lessen in adulthood. In mild hyperopia, the distance vision is clear while near vision is blurry. In more advanced hyperopia, vision can be blurred at all distances
Astigmatism Refraction unequal in different parts of eyeball. It usually occurs when the front surface of the eye, the cornea, has an asymmetric curvature. Normally the cornea is smooth and equally curved in all directions, and light entering the cornea is focused equally on all planes, or in all directions. See topic
Presbyopia Age-related diminution in near vision. Onset usually noticed around ages 40+ years. The lens of the eye becomes more rigid and does not flex as easily. As a result, the eye loses its focusing ability and it becomes more difficult to read at close range. This normal ageing process of the lens can also be combined with myopia, hyperopia or astigmatism. There is no way to slow down or reverse presbyopia
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