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Vision
Care Center | What
is LASIK? | When is
LASIK not for me?
LASIK
Surgery Checklist | Glossary
What is LASIK?
The eye and vision errors
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: 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. Glasses or
contact lenses are designed to compensate for the eye's
imperfections.
Surgical procedures aimed at improving the focusing
power of the eye are called refractive surgery. In LASIK surgery,
precise and controlled removal of corneal tissue by a special laser
reshapes the cornea changing its focusing power.
Other types of refractive surgery
Radial Keratotomy or RK and Photorefractive Keratectomy or PRK are
other refractive surgeries used to reshape the cornea. In RK, a very
sharp knife is used to cut slits in the cornea changing its shape.
PRK was the first surgical procedure developed to reshape the
cornea, by sculpting, using a laser. Later, LASIK was developed. The
same type of laser is used for LASIK and PRK. Often the exact same
laser is used for the two types of surgery. The major difference
between the two surgeries is the way that the stroma, the middle
layer of the cornea, is exposed before it is vaporized with the
laser. In PRK, the top layer of the cornea, called the epithelium,
is scraped away to expose the stromal layer underneath. In LASIK, a
flap is cut in the stromal layer and the flap is folded back.
Another type of refractive surgery is thermokeratoplasty in which
heat is used to reshape the cornea. The source of the heat can be a
laser, but it is a different kind of laser than is used for LASIK
and PRK. Other refractive devices include corneal ring segments that
are inserted into the stroma and special contact lenses that
temporarily reshape the cornea (orthokeratology).
Source: U.S. FDA Center for
Devices and Radiological Health
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Note: The above information is intended to supplement, not substitute
for, the expertise and judgment of your physician, pharmacist, or other
healthcare professional. It is not intended to diagnose a health
condition, but it can be used as a guide to help you decide if you
should seek professional treatment or to help you learn more about your
condition once it has been diagnosed.
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