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This excerpt taken from the EYE 10-K filed Mar 14, 2006. Refractive Disorders. Refractive
disorders, such as myopia, hyperopia, astigmatism and presbyopia, occur when
the lens system is unable to properly focus images on the retina. For example,
with myopia (nearsightedness), light rays focus in front of the retina because
the curvature of the cornea is too steep. With hyperopia (farsightedness),
light rays focus behind the retina because the curvature of the cornea is too
flat. Astigmatism makes it difficult for a person to focus on any object
because the otherwise uniform curvature of the cornea or lens is somehow disrupted
or becomes uneven. Presbyopia is the progressive loss of flexibility of the
lens and its ability to change shape to focus on near or far objects, and is
presumably caused by aging of the eye’s lens and the muscles that control the
shape of the lens.
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