Nearsightedness is caused either
by the cornea (the front window of the eye) being curved too
steeply, the axial length of the eye being too long or a combination
of both. When this occurs, the light entering the eye is focused
in front of the back of the eye and makes objects at a distance
blurred. Consequently the individual is able to see better
at near hence the term nearsightedness!
Image focuses in front of the retina in nearsighted
patients |
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Farsightedness is caused either
by the cornea (the front window of the eye) having too flat
a curve, the axial length of the eye being too short, or a
combination of both. When this condition is present, the light
entering the eye is focused behind the back of the eye and
makes objects at near more difficult to see. The farsighted
individual can use their focusing system to compensate for
their refractive problem, so may not have problems seeing
clearly, but tend to have problems with eyestrain. With high
degrees of farsightedness the eyes may cross when the individual
tries to focus to see an object clearly.
Image
focuses behind the retina in farsighted patients |
 |
Astigmatism is caused primarily
by the shape of the eye. Rather than the cornea having
a round or spherical shape, like a basketball, it’s
more like someone squeezing the ball and creating a distorted
shape. A football is an example of an object that has a distorted
shape, being flatter along one meridian and steeper along
the other. Consequently, the light entering the eye is focused
in two different points rather than one. With astigmatism
if the individual is looking at the letter T they are not
able to get both the vertical and horizontal components of
the letter in simultaneous focus. Either the cross bar is
clear and the vertical bar is blurred or vice versa. Astigmatism
affects clarity of vision at all distances.
Image
focuses in 2 points instead of one point |
 |
Correction of these problems can be achieved with glasses,
contact lenses and laser surgery.
