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PRK (Photorefractive Keratectomy) is a
vision correction procedure which uses a laser to reshape the
cornea. and takes just a few minutes and is done under topical
anesthesia.
The cornea is a part of the eye that helps focus light to create
an image on the retina. It works in much the same way that the
lens of a camera focuses light to create an image on film. The
bending and focusing of light is also known as refraction.
Usually the shape of the cornea and the eye are not perfect and
the image on the retina is out-of-focus (blurred) or distorted.
These imperfections in the focusing power of the eye are called refractive
errors. There are three primary
types of refractive errors: They are myopia, hyperopia and astigmatism. Persons
with myopia, or
nearsightedness, have more difficulty seeing distant objects as clearly as near
objects. Persons with
hyperopia, or farsightedness, have more difficulty seeing near objects as
clearly as distant objects.
Astigmatism is a distortion of the image on the retina caused by irregularities
in the cornea or lens of
the eye. Combinations of myopia and astigmatism or hyperopia and astigmatism are
common.
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MYOPIA
(Nearsighted) |
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HYPEROPIA
(Farsighted) |
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Light rays are focused
in front of the retina instead of directly on the retina |
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Light rays are not bent
enough to focus directly on the retina |
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ASTIGMATISM |
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PRK |
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Light rays are focused
at more than one point on the retina |
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The Cornea is reshaped
so light rays can focus directly on the retina |
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To treat nearsightedness, the cornea is made flatter by
removing tissue from the center of the cornea.
To treat farsightedness, the flat cornea is made steeper by
removing peripheral tissue in a ring shape on the outer edges of
the cornea. This steepens the central visual part of the cornea.
To treat astigmatism, the cornea is made less oval
shaped. Astigmatism means that the eye has an oval or football
shape.
The laser reduces the oval shape making the focusing
ability clear in all directions. Astigmatism can be treated at
the same time as nearsightedness and farsightedness.
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