are several methods for performing laser eye surgery, but all of them involve
using a laser to reshape the cornea. Here are the main types.
uses the Microkeratome to make a flap on the cornea, which gets temporarily
put aside, while lasers are used to remove the layers of tissue under the
cornea. Where and how much tissue is taken out determines the amount and
type of correction. (For farsightedness, the tissue removed is mostly
around the edge, leaving a small build up in the center of the eye, which
effects the vision. For nearsighted eyes, the tissue is made flatter
in the center of the eye, changing the vision.) Then the flap is replaced.
After surgery, it takes a few hours to heal. LASIK can be used to
improve farsightedness, nearsightedness, or astigmatism. LASIK is
considered state-of-the-art and is the most commonly used laser eye surgery.
(Photorefractive Keratoplasty) uses a laser to remove tissue, but, unlike
LASIK, it also removes the surface layer. But the surface of the
cornea contains elements that are critical for stable vision. So,
though the eye replaces and heals the surface over time, those elements
were taken out, causing problems for the eye. Visual stability can
take years to achieve after surgery. (The reason for the instability
is because after the surgery, the eye tries to heal itself in a process
called remodeling. With LASIK, the surface is never violated, therefore
the tendency for remodeling is greatly reduced.)
(Radial Keratotomy) corrects mild forms of nearsightedness, by making small
incisions in a radial pattern on the cornea, therefore flattening it.
But a major concern about RK is the way that the incisions weaken the eye.
Another concern is that eyes with RK can experience progressive flattening,
making them farsighted over time. The effect is worse for eyes undergoing
larger amounts of correction, and that is why today RK is usually replaced
by LASIK surgery. RK is the oldest of the modern refractive procedures.
(Automated Lamellar Keratoplasty) corrects nearsightedness by removing
a thin layer from the surface of the cornea, leaving it aside, and removing
a layer of the cornea underneath it. But when the surface layer is
replaced, some of the cornea has been taken away, leaving it thinner and
flatter than it was originally. ALK has the advantage of leaving
the corneal strength intact, unlike RK. The disadvantage is that
it is not as precise as the laser in removing tissue, and therefore it
sometimes takes multiple procedures to obtain the right amount of correction.
ALK has recently been replaced by LASIK.