What is Astigmatism? Definition
Astigmatism is one of a
group of eye conditions, called refractive
errors, that cause a disturbance in the way
light rays are focused within the eye. This
occurs when the cornea, a thin sheet of
clear tissue covering the eye around the
pupil, is irregularly curved. Normally, the
eye is a near-perfect sphere, but in
astigmatism, the front surface of the cornea
is curved more in one direction than in the
other--more football-shaped than
basketball-shaped. In fact, most astigmatic
corneas have two axes of irregular
curvature, one flatter than the other. This
distortion causes an inability of the eye to
focus light rays correctly onto the retina
and may result in vision resembling the
distortion in a funhouse mirror. This
blurred vision applies to objects at all
distances, though the condition may be
accompanied by near- or far-sightedness.
Unequal astigmatism may ultimately lead to
amblyopia, or "lazy eye," a condition in
which one eye suffers loss of acuity due to
the patient favoring his or her other, less
astigmatic, eye.
Astigmatism can be Mild or Serious
Not all people with
astigmatism require medical assistance; the
distortion can be fairly mild. Some experts
believe all human beings have a degree of
astigmatism. However, in many cases the
curvature of the eye is more severe, and
corrective lenses must be used to refocus
light rays in the eye. These corrective aids
may take the form of spectacles or contact
lenses. Many astigmatic patients use
specially curved contact lenses called toric
lenses, which include an additional power
element called a cylinder. These lenses bend
incoming light farther in one direction than
in another in order to oppose the refractive
effects of eye curvature. Astigmatism may
also be corrected by a refractive surgical
procedure called laser-assisted in-situ
keratomileusis, or lasik for short. Radio
keratotomy and astigmatic keratotomy are two
older forms of corrective corneal surgery.
Symptoms
Symptoms of astigmatism
include blurring or distortion of images at
all distances, plus headache, fatigue, eye
irritation, and frequent squinting. These
symptoms may grow more intense as a person
gets older, so it's a good idea to get
regular eye check-ups, especially if a
person has already been fitted for
corrective lenses. The patient's
prescription may need to be altered in order
to correct for changes in eye curvature.
Diagnosis
Astigmatism is easily
diagnosed by a standard ophthalmic exam that
includes a refraction test. Special tests
are seldom required. Children, or other
patients who are unable to respond to
questions, can have their refractive errors
measured by a test (called retinoscopy) that
uses reflected light.
Astigmatism is usually
present from birth. Its cause is unknown.
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