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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.
In LASIK
surgery, precise and controlled removal of corneal
tissue by a special laser, reshapes the
cornea changing its
focusing power. LASIK is a procedure that permanently
changes the shape of the
cornea, the clear covering
of the front of the eye, by using an excimer laser. A knife, called a
microkeratome, is used to cut a flap in the
cornea. A hinge is left at one end of this flap. The
flap is
folded back revealing the stroma, the middle section of
the cornea. Pulses from a computer-controlled
laser vaporize a
portion of the stroma and the flap is replaced.
(Courtesy of the FDA) |
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