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 The
cornea and lens combine to focus visual images on the back of
the eye. When the overall length of the eye is incorrect or
when the curvature of the cornea is incorrect, the visual images
are not in focus. The cornea accounts for approximately 2/3rds
of the focusing power of the eye. By surgically changing the corneal
curvature, visual images can be brought into focus.
Laser
In Situ Keratomileusis (LASIK) and Photo-Refractive Keratectomy
(PRK) are two surgical techniques which utilize the excimer
laser to reshape or change the curvature of the cornea.
LASIK utilizes conventional and laser surgery to correct
nearsightedness, farsightedness and astigmatism. LASIK can
correct nearsightedness and farsightedness with or without astigmatism,
with excellent results (95% of patients achieve 20/40 vision or
better).
In
performing LASIK, eye drop anesthetic is used to numb the
eye. The surgeon then uses a special instrument to create a corneal
flap. The flap is retracted and the eye is positioned under the
excimer laser (which has been computer programmed to remove microscopic
amounts of the internal corneal tissue). Removal of the tissue
changes the curvature of the cornea. If the patient is nearsighted,
tissue closer to the central part of the cornea is removed to
decrease the curvature or flatten the cornea. If a patient is
farsighted, tissue in the peripheral part of the cornea is removed
to increase the curvature of the cornea. To correct for astigmatism,
tissue is removed along the axis of the astigmatism. After the
laser has been used, the flap is returned to its original position.
The corneal tissue has extraordinary natural bonding qualities
that allow effective healing without the use of stitches.
Since
only local anesthetic is used, patients remain awake during
the procedure. The entire procedure takes only a few minutes.
Improved vision is often possible on the day following the surgery.
Eye drops and night protection are necessary for designated periods
of time.
PRK
Photo-Refractive
Keratectomy, PRK is another method of surgically reshaping
the cornea using the excimer laser. The difference between LASIK
and PRK is that for PRK, the corneal flap is not created. That
is, the outer layer of the cornea remains in place and the laser
removes tissue directly from this outer layer. PRK can be used
for low to moderate amounts of nearsightedness. The healing period
for PRK is longer and usually only one eye is treated at a time.
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