Refractive Problems: Myopia, Hyperopia, Astigmatism, Presbyopia
Do any of these problems sound like you?
It may sound like Greek, but the
words myopia, hyperopia, astigmatism,
and presbyopia describe vision problems that afflict countless millions of people of all ages.
All of these terms come together
to describe what are known as “refractive errors.”
Refraction refers to the ability of the eye to focus light.
The shape of the cornea, the strength of the lens and of the
eye, and the length of the eyeball determine how clearly you
see. If even one of these factors is not coordinating properly
with the others, light will not focus correctly and your vision
will not be clear.
Myopia —commonly
called nearsightedness—is the most common refractive
error. People with myopia can see objects closer to them,
but have difficulty focusing on distant objects. The condition
is caused by a cornea that has more curvature than normal,
or an eyeball that is too long. In either case, light is focused
at a point in front of the retina, causing a blurred image.
About one in four American adults are myopic. The condition
usually begins in childhood, and often stabilizes in the late
teen years or twenties.
Hyperopia is farsightedness, the opposite of myopia. For some people
with hyperopia, objects at a distance are clear, while objects
up close are blurry with uncorrected vision. This is caused
by a flatter-than-normal cornea, or an eyeball that is too
short—causing light to focus on a position behind the
retina.
Astigmatism ,
or ovalness of the cornea, is another refractive problem.
With this condition, there is typically a distortion of the
cornea that tilts or bends the image due to an unequal bending
of light as it attempts to focus. People with a high degree
of astigmatism have difficulty focusing properly at any distance,
and experience a “ghosting” or “doubling”
effect with the images they view. Nearsighted and farsighted
people may also have some degree of astigmatism.
Finally, presbyopia is a very common condition that is simply part of the normal
aging process. Presbyopia develops as the lens of the eye
loses flexibility, typically between the ages of 40 and 50.
Those who are farsighted or nearsighted find they need to
wear bifocals, and those with normal vision will need to wear
reading glasses. If patients with presbyopia have corrective
laser surgery for either myopia or hyperopia, they will probably
need to wear corrective lenses for reading.
In recent years through technological advances, ophthalmologists and researchers have devised increasingly
effective ways to overcome or minimize most of these conditions
- - most notably, the development of the LASIK surgical procedure.
