 Nearsightedness
(or Myopia)
Myopia is the medical term for nearsightedness, and refers to a condition in
which an individual is able to see objects that are close clearly but sees distant
objects out of focus.
The cornea and lens of the eye work together to properly focus visual images
on the retina. If an image is out of focus, it is because the cornea is too steep
or the shape of the eye is too long. When this occurs, visual images are focused
in front of the retina and myopia occurs.
Myopia normally starts to appear between the ages of eight and twelve years
old, and almost always before the age of 20. Myopia affects nearly 30% of the
U.S. population. Once myopia starts, and as the body grows, the condition often
worsens. It usually stabilizes in adulthood. Changes in eyeglasses or contact
lens prescriptions are necessary during growth periods.
 Farsightedness
(Hyperopia)
Hyperopia is a medical term for farsightedness. It is a vision condition in
which the eye has more difficulty seeing up close than at a distance.
The cornea and lens of the eye work together to properly focus visual images
on the retina. If an image is out of focus, it is because the cornea does not
have the proper curvature. Hyperopia occurs when the eye is smaller than normal,
or the cornea is flattened. When this happens visual images are focused behind
the retina.
Usually this condition is undetected until later in life because when we are
young the eye is able to compensate for the hyperopia by contracting the internal
lens of the eye.
 Astigmatism
Astigmatism is a vision condition that occurs when the cornea is curved more
in one direction than another. The irregular shape of the cornea prevents light
from focusing properly on the retina at the back of the eye. As a result, objects
may appear blurred at all distances.
In a few cases, astigmatism is caused by lid swellings and corneal scars, or
by keratoconus, a rare condition in which the cornea becomes misshapen and pointed,
when it should be smooth and rounded.
Presbyopia
 Presbyopia
is a vision condition in which the lens loses its flexibility, making
it difficult to focus up close. During the early and middle years
of life, the lens of the eye has the ability to focus both near
and distant images by getting thicker for near objects and thinner
for objects at a distance. When this ability is lost, presbyopia
results.
Presbyopia usually becomes noticeable in the early to mid-forties. As we age,
the lenses in the eye lose some of their elasticity, and without elasticity they
lose some of their ability to change focus for different distances. The loss of
flexibility takes place over number of years, but it may seem to occur suddenly.
Only when the loss of elasticity impairs vision to a noticeable degree is the
change recognized.
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