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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