Comparing LASIK and PRK

by Jennifer Kimberley


LASIK (Laser Assisted in-situ Keratomileusis) and PRK (Photorefractive Keratectomy) are types of refractive surgery, meaning that they change the way your eyes bend light. They both use an excimer laser to vaporize tiny pieces of unwanted tissue from the cornea, the front clear part of the eye. The laser is a cool ultraviolet laser which does not burn the eye, and is programmed according to your treatment plan to penetrate only to certain depths.
Light Refraction
When light enters the eye, it is bent (refracted) by the cornea's curved shape, and then bent some more by the eye's lens. The lens is behind the iris, the colored part.

In a 20/20 eye, the cornea and lens between them refract incoming light at exactly the right angles to make it all focus clearly on the back of the eye. The retina is the inside surface of the back, and is filled with light-sensitive cells. These nerve cells receive the light, forming a tiny upside-down image of what you're looking at. They convert this image information to neural (electrical) information and send it via the optic nerve to the brain's vision center.

Conditions Treated by LASIK and PRK
If you have blurry vision, there could be several reasons why, but not all would involve the bending of light. LASIK and PRK can improve vision only if the cause of poor vision is incorrect light refraction.

There are three such conditions:
* Nearsightedness (myopia - light is being bent too much and is focusing in front of the retina
* Farsightedness (hyperopia) - light is not being bent enough, and is focusing behind the retina
* Astigmatism - the cornea is oval-shaped like a football, with two curvatures, and is bending light two ways (more sharply on the steeper curvature and less sharply on the flatter curvature). This gives blurry vision.

How LASIK Works
Wavefront-guided LASIK is the most sophisticated and accurate of the ways LASIK is done. Your eye surgeon will have a complete LASIK system that includes both diagnostic and treatment aspects. The term wavefront refers to the diagnostic light which is shone into each eye. It reflects back to the LASIK system in a modified form - the front of the light wave is wavy in a pattern which expresses the microscopic contours of your eye.

A 3-dimensional map is made from this returning light pattern, one for each eye. Your LASIK surgeon will base your treatment plan on this information, and since the treatment laser is part of this same LASIK system, the 3-D map can guide the laser as it works on your eye.

* First, a thin flap is cut in the corneal surface, to expose the layer beneath. It is folded back out of the way while treatment proceeds.
* The treatment laser vaporizes tiny pieces of corneal tissue according to your treatment plan.
* This reshapes the corneal curvature to give your clear vision.
* The flap is folded back and smoothed down gently. It will heal without any sutures.

You will have clear vision immediately after your LASIK procedure, and can go home the same day, with someone driving you. Most people rest until the next day, and then return to normal activities.

How PRK Works
There is no flap made on the corneal surface. To expose the stromal layer below, your LASIK surgeon would remove surface tissue altogether, with a special instrument. Then laser treatment is done as it is for LASIK, and instead of folding a corneal flap back over the treated area, a bandage contact lens is inserted.

The eyes take longer to heal after PRK, and you'll feel more discomfort. But the corneal surface - epithelium - is like our skin surface in some ways. It continually discards old cells and replaces them with new ones. So the cornea can heal itself very well and quickly. You would wear the bandage contact lenses until your LASIK surgeon judged it time to remove them - probably a week or so.

As with LASIK, you will immediately have clear vision, but will not notice it so much until the eyes have healed.

Advantage of PRK
It avoids all the possible complications that the LASIK flap can cause. Sometimes that flap does not heal correctly, but forms wrinkles in itself which distort vision. A second surgery can correct that. In rare cases, the flap is created wrongly, with no hinge, or with a hole in the center, or uneven thickness. Good patient screening almost always prevents flap complications, but with PRK they are not possible at all.

Choosing between LASIK and PRK would be done in discussions with your LASIK surgeon. The first step is to schedule an initial consultation. Be sure to choose a highly-trained and well-experienced eye surgeon who is thorough in screening patients. LASIK and PRK are not suitable for everyone, and a successful outcome will depend on careful screening.

About the Author
Contact Western Laser Eye Associates today for more information about refractive eye surgery and to schedule an appointment.