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LASIK & Vision Surgery
There are several types of surgery designed to address common refractive
errors, including myopia,
hyperopia, and
astigmatism. The most popular of
these are outlined below.
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LASIK
LASIK refers to 'laser assisted in situ keratomileusis'. It is a surgical
procedure wherein the shape of a patient's cornea is permanently altered.
The surgery is accomplished using an instrument called an excimer laser.
The FDA initially approved the use of excimer laser's in a type of vision
surgery called PRK. PRK was used to treat myopia and astigmatism. In the
past many years, these lasers have increasingly been used in the surgical
procedure referred to as LASIK, which has now become the most common
vision surgical procedure in the United States and elsewhere. LASIK and
other vision surgeries such as PRK and RK are all designed to correct
refractive errors. For this reason, the methods are often called
refractive surgeries. LASIK is used to correct the most common refractive
errors, including myopia, hyperopia, and astigmatism.
The cornea is a critical part of the physiology of the eye and vision. The
cornea is the clear cover at the front of the eye and it's primary role is
to focus light waves that enter the eye back onto the retina. Just as a
camera focuses light to create an image, the cornea bends and focuses
light to form an image on the retina, a process called refraction. When
the cornea is misshapen, the image on the retina appears out of focus,
blurred or distorted. The improper focusing of the eye results in
'refractive errors'. There are three primary types of refractive errors,
including myopia (nearsightedness), hyperopia (farsightedness), and
astigmatism. More often than not, vision impairment is a result of a
combination of these types of refractive errors.
LASIK surgery involves the removal of tissue from the cornea using a
laser. This results in the cornea being reshaped to address refractive
errors. The process begins with a surgical cut into the cornea, creating a
flap. This cut is not complete, but leaves one section attached so that is
can be folded back. When folded, the surgeon can access the middle of the
cornea, called the stroma. Laser pulses are used to remove a part of the
stoma, then the flap is folded back into position. The removal of tissue
from the cornea allows the surgeon to reshape the cornea so that light is
refracted properly to the retina, solving a patient's particular
refractive problems.
Other Types of Refractive Surgeries
1) PRK (Photorefractive Keratectomy)
PRK was the first kind of vision surgery used to reshape the cornea. Like
LASIK, an excimer laser is used to reshape the cornea; however, unlike
LASIK, no flap is cut. Instead, the top layer of the cornea, called the
epithelium, is scraped away to reveal the stroma. PRK is an effective
surgical technique, but requires a longer recovery period. Some surgeons
still prefer PRK to LASIK, particularly to address certain types of
refractive errors. PRK is most often used to treat astigmatism and
hyperopia.
2) RK ( Radial Keratotomy)
RK is used to treat myopia and was once a far more common method than it
is today. Over 1 million Americans underwent the procedure in the 1980s.
Lasers are not used in RK. Instead, slits are cut into the cornea using a
sharp, surgical knife. The slits allow a surgeon to reshape the cornea,
causing a relaxing and flattening of the central cornea.
3) LTK (Thermokeratoplasty)
This type of refractive surgery is used to treat hyperopia
(farsightedness). In LTK, heat is used to reshape the cornea. Laser heat
is used; however, the laser used is a holmium YAG laser, different than
that used in LASIK or PRK. No removal of tissue occurs. Instead, the laser
is used to shrink the collagen fibrils in the peripheral cornea. The
effect is an increase in the steepness of the central cornea, thus
reducing farsightedness.
4) Intacs (Intracorneal rings)
Intacs are a very recent development in the treatment of myopia. They
arguably offer a distinct advantage over treatment with LASIK or PRK in
that the process is reversible or 'changeable', allowing a patient to
address changes in vision requirements over time. In this procedure,
extremely thin intracorneal rings are inserted into the cornea, causing
changes to the curvature of the cornea. The rings require no maintenance
and cannot be felt when in the eye. This surgery is presently only
available to those U.S. citizens with low degrees of myopia.
Other types of surgeries designed to correct refractive errors exist and
are been studied in clinical trials. These surgeries hold much promise for
the increasingly effective treatment of all types of refractive errors.
Phakic IOL (implantable contact lenses) is only one example of a new
technique that may, in time, revolutionize the treatment of refractive
patients with ever more precision.
If you want to consider vision surgery to address your vision
requirements, talk to your eye doctor about what method may best suit your
needs.
Resources: Learn about
LASIK surgery and if you're a good
candidate. Read detailed
information about LASIK from the FDA.
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