The Refractive Errors
When light enters the eye, it is bent, or refracted, by a clear tissue on the front of the eye called the cornea. The
cornea, in effect acts like a lens to focus incoming light onto the retina on the back of the eye.
Myopia, or nearsightedness
The light entering the eyes does not focus on the retina as it
should, but instead focuses at a point in front of the retina.
The result is that distant objects appear blurry, while near
objects appear clear.
Hyperopia, or farsightedness
The light entering the eye focuses at a point behind the
retina. The result is that near objects appear blurry, while
distant objects appear clear. In some cases, hyperopia may
cause blurriness at both distance and near because of
accommodation to see clearly, causing asthenopia.
Astigmatism
In astigmatism, the cornea is not spherical or basketball-shaped as it is in the normal
eye; rather, it is shaped more like an American football (elliptical). The light rays
entering the eye fail to come to a single focal point. The result is that objects are not
focused into a single image on the retina, causing vision to be distorted or blurry for
distance and near. Astigmatism can accompany nearsightedness or farsightedness.
Presbyopia
From the Greek language meaning “old eye.” It is the inability to focus on objects up
close due to loss of the accommodation power. This occurs normally with age and usually becomes apparent in
people in their early forties.