Lasik | What Is Lasik Surgery?
LASIK stands for Laser-Assisted In Situ
Keratomileusis and is a procedure that permanently changes
the shape of the cornea, the clear covering of the front of the
eye, using an excimer laser. A mechanical microkeratome (a blade
device) or a laser keratome (a laser device) is used to cut a flap
in the cornea. A hinge is left at one end of this flap. The flap is
folded back revealing the stroma, the middlesection of the cornea.
Pulses from a computer-controlled laser vaporize a portion of the
stroma and the flap is replaced. There are other techniques and
many new terms related to Lasik that you may hear
about.
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.
Refractive
Surgery To Correct Myopia, Hyperopia &
Astigmatism
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.
Watch a animation movie of the Lasik
procedure.
Other
Types Of Refractive Surgery
Radial Keratotomy (RK) and Photorefractive
Keratectomy (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. Food and Drug Administration, Center for Devices
and Radiological Health
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