If you experience a distortion or blurring of images
at all distances, nearby as well as far, you may have
astigmatism. Even if your vision is fairly sharp, headache,
fatigue, squinting and eye discomfort or irritation may indicate
a slight degree of astigmatism. A thorough eye examination,
including tests of near vision, distant vision and vision clarity,
can determine if astigmatism is present. Astigmatism is not a
disease. It simply means that you have a variation or
disturbance in the shape of your cornea.
Astigmatism is one of a group of eye conditions known
as refractive errors. Refractive errors cause a disturbance
in the way that light rays are focused within the eye.
Astigmatism often occurs with nearsightedness and
farsightedness, conditions also resulting from refractive errors.
Astigmatism usually occurs when the front surface of
the eye, the cornea, has an irregular curvature. In
astigmatism, the front surface of the cornea is curved
more in one direction than in the other. With the cornea’s
shape more like that of an American football or rugby ball
than a basketball, the light hitting the more curved surface
comes to a focus before that which enters the eye through the
less curved surface. Thus, the light is focused clearly along
one plane, but is blurred along the other so only part of
anything being looked at can be in focus at any time.
This abnormality may result in vision that is much like
looking into a distorted, wavy mirror. The distortion
results because of an inability of the eye to focus
light rays to a point.
Not all corneas are perfectly curved, just as sets of
teeth are seldom perfectly aligned. The degree of variation
determines whether or not you will need corrective eyewear.
If the corneal surface has a high degree of variation in its
curvature, light refraction may be impaired to the degree that
corrective lenses are needed to help focus light rays better.
The exact reason for differences in corneal shape remains
unknown, but the tendency to develop astigmatism is
inherited. For that reason, some people are more prone to develop astigmatism than others.