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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, a 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. The lasik flap
is
created using a highly sophisticated and accurate
instrument known as a "microkeratome", to
create 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.
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