The cornea and lens
combine to focus visual images on the back of the eye. When the overall
shape 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, most or all of the blur can be eliminated.
Laser In Situ Keratomileusis (LASIK) and Photo-Refractive Keratectomy
(LASIK) are two surgical techniques which utilize lasers to reshape
or change the curvature of the cornea.
LASIK had its origins
about thirty years ago and was originally developed to treat patients
who had very poor vision due to corneal disease. It has now evolved
into a successful technique for correcting refractive errors. The current
procedure, done on an outpatient basis, involves both the use of conventional
and laser surgery to correct nearsightedness, farsightedness and astigmatism.
LASIK can correct a much higher degree of nearsightedness with or without
astigmatism than any other refractive procedure, 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 cut into and behind a layer
of the cornea. A portion of the cornea is peeled back to create a flap
and expose the inner portions of corneal tissue. The eye is then 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, selected tissue at certain
angles is removed to insure that the cornea curves equally in all directions.
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.
Advantages of LASIK include:
- Faster healing
- Rapid visual
- Less risk of
- Less risk of
- Less post-op
- The second eye
can be done within a week
- Treatment of
a wider range of nearsightedness
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. During LASIK , a part of the cornea is peeled back
so that the laser removes tissue from the inner corneal layers. PRK
is used for low to moderate amounts of nearsightedness.
Just as in LASIK, the laser treatment requires less than a minute. But
unlike LASIK, the healing period time is longer. The correction for
nearsightedness, farsightedness and astigmatism is the same as in LASIK.
The corneal curvature is changed so that the visual images are properly
focused on the back of the eye.