How it Works
Excimer Laser Surgery for Myopia
Laser light is capable of performing surgical procedures too delicate for the finest scalpel. This makes laser light the ideal tool to use on the eye. The term "laser" is an acronym for "Light Amplification by Stimulated Emission of Radiation," which is the scientific description of the method for creating this intense beam of light.
The excimer laser uses a mixture of argon and fluorine gases to produce a slender beam of invisible ultraviolet light energy. This ultraviolet light has a much shorter wavelength than the ultraviolet light in sunlight that causes sunburn.
The excimer laser does not burn the eye. It removes only 1/4 of a micron (an amount invisible even with a normal examining microscope, representing about one ten-millionth of an inch) of cornea with each pulse. The excimer laser energy first breaks up the molecular bonds in the cornea's collagen connective tissue, and then scatters the small molecules into the air. This process is call photo-ablation.
In laser vision correction, the excimer laser is used to reshape the curvature of the eye so that light becomes focused crisply on the retina. This can reduce your dependency on glasses or contact lenses. The reshaping may be carried out in one of two ways: on the surface of the cornea, with photorefractive keratectomy (PRK), or under the surface of the cornea, with laser in-situ keratomileusis (LASIK).
Customized Laser Vision Correction
Excimer lasers have been used to correct the nearsightedness, farsightedness and astigmatism of over six million people worldwide. An estimated 98% of these patients are now seeing 20/20 to 20/40 without glasses. With such impressive results, how could you expect laser vision correction to improve?
Since the mid-1800s doctors have measured vision by having patients read letters on a standard Snellen Eye Chart. Doctors consider your vision "normal" if you can identify the small letters on the 20/20 line from a distance of 20 feet. But scoring 20/20 on your vision test doesn't necessarily mean you have excellent vision, especially if the letters you are able to identify are not crisp and clear.
Until now, laser vision correction, like glasses and contacts, could only correct the visual distortions caused by nearsightedness, farsightedness and astigmatism. However, these three common types of vision distortions, called "lower order aberrations," are only responsible for 85-90% of the overall quality of your vision. There are other imperfections on your eye's optical system that may affect the clarity of your vision and how well you see at night or in low light. Doctors call these visual distortions "higher order aberrations" and they can cause a glare, shadows, halos and other annoying visual effects. Unless these higher order aberrations are addressed along with the lower order aberrations, the quality of your vision may not be ideal, even if you have measurable vision of 20/20.
Now, thanks to advanced wavefront technology, it's possible to measure and address both lower and higher order aberrations. Here's how it works: First, flat waves of light are passed through your eye using a computerized wavefront-measuring instrument, and as the light waves travel through your eye's optical system, the distortions in your vision are measured. The diagnostic unit captures the distorted waves as they exit your eye and compares them to the perfectly flat light waves that would have been reflected if your optical system were perfect. Next, a map is generated representing your unique visual distortions, including both lower and higher order aberrations. This map is a guide for the laser, telling it how and where to reshape the cornea to correct your vision.
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