What is Refractive Error?
Refractive error prevents light rays from being brought to a single
focus on the retina resulting in reduced visual acuity. To see clearly,
refractive errors are most often corrected with ophthalmic lenses
(glasses, contact lenses). The three principal types of refractive
conditions are myopia, hyperopia, and astigmatism. Another
ophthalmic condition that also results in blurred near vision is called
presbyopia. Presbyopia is a progressive loss of accommodation
(decreased ability to focus at near distance due to physiological
changes in the eye’s crystalline lens) that normally occurs around 40
years of age. Bifocals or reading glasses are necessary to correct this
condition.
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Myopia (nearsightedness, distant objects appear fuzzy) is a condition in which light rays are focused in front of the retina. About 30% of Americans are myopic.
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Hyperopia (farsightedness, near objects appear fuzzy) is a condition
in which light rays are focused behind the retina. An estimated
40% of Americans are hyperopic. However, this number may not
be accurate. Young hyperopes (< 40 years), who can compensate
for their farsightedness with their ability to accommodate, are often
not counted in this number and some studies incorrectly include
presbyopes, who also require plus power lenses to see clearly.
Astigmatism is a condition often caused from an irregular curvature
of the cornea. As a result, light is not focused to a single image on the
retina. Astigmatism can cause blurred vision at any distance and may
occur in addition to myopic or hyperopic conditions. Approximately
60% of the population has some astigmatism.
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What is Laser Refractive Surgery?
In October 1995, the Food and Drug Administration (FDA) approved
the use of the excimer laser to perform a refractive procedure
called Photorefractive Keratectomy (PRK). PRK improves visual
acuity by altering the curvature of the cornea through a series of
laser pulses. The laser photoablates (vaporizes) the corneal tissue
to a predetermined depth and diameter. PRK can be used to correct
myopia, hyperopia, and astigmatism. Reported PRK problems such
as postoperative pain, prolonged healing period, increased risk of
infection, and glare (halos) at night, has resulted in Laser in situ
Keratomileusis (LASIK) becoming the preferred choice for refractive
surgery by patients and eyecare practitioners. A survey in the United
States found that the percentage of refractive surgeons performing
PRK had decreased from 26% in 1997 to less than 1% in 2002.
LASIK is performed using two FDA approved devices: the
microkeratome and excimer laser. During the LASIK procedure, the
microkeratome slices a thin fl ap from the top of the cornea, leaving
it connected by a small hinge of tissue. The corneal fl ap is folded
aside and the excimer laser is used to reshape the underlying corneal
stroma. The flap is then returned to its original position.
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Is LASIK an Option for Me?
An eye care specialist should thoroughly evaluate your current
ocular health and correction requirements to determine whether you
are a suitable candidate for refractive surgery.
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