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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.
(See the animation of the LASIK procedure and what should I expect before, during, and after surgery.)
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).
What the FDA regulates
In the United States, the Food and Drug Administration (FDA) regulates
the sale of medical devices such as the lasers used for LASIK. Before a
medical device can be legally sold in the U.S., the person or company
that wants to sell the device must seek approval from the FDA. To gain
approval, they must present evidence that the device is reasonably safe
and effective for a particular use, the "indication." Once the FDA has
approved a medical device, a doctor may decide to use that device for
other indications if the doctor feels it is in the best interest of a
patient. The use of an approved device for other than its FDA-approved
indication is called "off-label use." The FDA does not regulate
off-label use or the practice of medicine.
The FDA does not have the authority to:
- Regulate
a doctor's practice. In other words, FDA does not tell doctors
what to do when running their business or what they can or cannot tell
their patients.
- Set the amount a doctor can charge for LASIK eye surgery.
- "Insist" the patient information booklet from the laser manufacturer be provided to the potential patient.
- Make
recommendations for individual doctors, clinics, or eye centers.
FDA does not maintain nor have access to any such list of doctors
performing LASIK eye surgery.
- Conduct or provide a rating system on any medical device it regulates.
The
first refractive laser systems approved by FDA were excimer lasers for
use in PRK to treat myopia and later to treat astigmatism. However,
doctors began using these lasers for LASIK (not just PRK), and to treat
other refractive errors (not just myopia). Over the last several years,
LASIK has become the main surgery doctors use to treat myopia in the
United States. More recently, some laser manufacturers have gained FDA
approval for laser systems for LASIK to treat myopia, hyperopia and
astigmatism and for PRK to treat hyperopia and astigmatism.
See the section on FDA-approved lasers
for more details on which lasers have received FDA approval and the
specific indications and treatment ranges for which they were approved.
Updated August 16, 2007
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