In ordinary circumstances,
the curvature of the cornea, the power of the lens and the length
of the eye are finely coordinated to focus images perfectly on the
retina and thereby produce clear, strain free vision. Sometimes
this system fails and light rays focus the image ahead or behind
the retina. This results in unclear vision, eye strain and headaches.
These conditions are known as refractive errors and can be of the
following types:
Nearsightedness
Technically called myopia, nearsightedness means you have trouble
seeing and resolving objects at a distance. When the eye is too
long in relation to the curvature of the cornea, images focus in
front of the retina instead of on it and objects at distances appear
blurred. Patients with myopia are able to see near objects.
Farsightedness
Technically called hyperopia, farsightedness means you have trouble
with close up vision. It occurs when the eye is functionally too
short. The rays of light are focused behind the retina producing
a blurred image. Some people who are farsighted are able to use
their focusing muscle (accommodation) to bring the image forward
allowing them to see clearly. This ability worsens with age and
reading glasses or bifocals may be needed. Farsighted people see
distance objects more clearly than near objects.
Aging eyes
The normal solution for refractive errors is to wear spectacles
or contact lenses to see clearly. There is one other condition for
which people normally need to wear glasses. This condition is normally
associated with aging, and is known as presbyopia.
Presbyopia is a normal aging process. As we get older, the lens
loses its ability to flex and focus at near objects. The onset of presbyopia
typically is between 40 and 50. When this occurs people who already
wear glasses may need bifocals and those who have never worn glasses
may require reading glasses. Presbyopia is an important concept
to understand, if you are over 40, and if you are considering laser
correction. One advantage of mild nearsightedness (myopia) is the
ability to remove your glasses after presbyopia sets in and still
be able to read. If you have Laser Vision Correction for nearsightedness,
you will lose this ability. That's because your vision typically
becomes normal, and normal for the aging eye usually will require
reading glasses for small print. The excimer laser has no effect
on your focusing muscles and therefore cannot treat presbyopia.
However, there are ways around this problem, and it is best to talk
to one of our expert eye doctors to discuss the best solution for
you.
Astigmatism
Many patients with myopia or hyperopia have some degree of astigmatism.
This means that your eye is slightly oval and your cornea is shaped
like a football rather than a sphere. People with astigmatism experience
distortion or tilting of images due to unequal bending of the rays
of light entering your eyes. High degrees of astigmatism will cause
blurred vision for distance and near objects.
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