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Laser Vision Correction

Laser vision correction is a technique used to permanently correct myopia, hyperopia, and astigmatism by reshaping the front surface of the eye, called the cornea. Ophthalmologists have been performing refractive surgery for many years, but advancements in laser technology have recently made laser refractive surgery much more safe, predictable and less expensive.

Is Laser Vision Correction for You?

Laser vision correction should not be taken lightly. If you are perfectly happy with your glasses or contact lenses and the vision they provide, then this procedure is probably not for you. If you are an outdoors or sports enthusiast, don't like or have trouble wearing glasses and contact lenses, and you want to be free of the hassles of those devices, laser vision correction is something you should consider. The procedure will give you much more visual independence.


Laser vision correction is unlikely to make your uncorrected vision better than it is right now with your contact lens or spectacle prescription. Put another way, laser vision correction will not improve you best corrected visual acuity. What laser vision correction will do is significantly reduce your dependence upon glasses or contact lenses. In some cases, an enhancement (second laser procedure) or mild (thin) prescription lenses will still be needed to sharpen up your vision. The higher your prescription is, the more likely you are to need an enhancement or prescription lenses after the initial laser vision correction procedure.

How Does Refractive Surgery Work?

Most refractive surgeries work by reshaping the cornea, which is the most powerful refracting surface of the eye. Small changes in the curvature of the cornea lead to relatively large changes in the focusing power of the eye. For myopia, the cornea is purposely flattened or reduced in curvature. For hyperopia, the cornea is purposely steepened. And for astigmatism, the cornea is purposely flattened and/or steepened to varying degrees in different directions, depending upon the orientation and magnitude of the astigmatism.

The Procedures

Several different procedures have been developed to correct near-sightedness, far-sightedness, and astigmatism (when the eye is shaped like a football instead of like a basketball). The most common ones are:

Radial Keratotomy (RK) is a surgical procedure in which radial incisions are made into the cornea to allow the periphery to bulge forward, resulting in flattening of the front surface of the cornea. Results are relatively unpredictable. This technique is principally used to correct near-sightedness and astigmatism.

Photorefractive Keratectomy (PRK) is a laser procedure in which a precisely determined thickness the outer layers of the cornea is vaporized and allowed to heal over, resulting in a new shape to the cornea. This technique can be used to correct myopia, astigmatism, and hyperopia.

Laser In Situ Keratomileusis (LASIK) is a laser vision correction procedure developed approximately 20 years ago and approved by the FDA approximately 5 years ago. It is very similar to PRK (above). One important step occurs before the laser ablation is performed: a thin flap is created with a microkeratome and it is folded back to reveal corneal stroma (the central tissue of the cornea), upon which the laser ablation is performed. The flap is then folded back into place. This procedure leaves most of the corneal epithelium intact and therefore heals quickly. This procedure can be used to correct significant amounts of near-sightedness, astigmatism, and far-sightedness. The long term outcome (5 to 10 years) of this procedure appears to be excellent, but we do not have much data beyond that.


How The Eye Works

The major anatomical components of the eye are illustrated in Figure 1. From the point of view of light entering the eye, the first refracting (light bending or focusing) structure is the cornea. Approximately two-thirds of the focusing power of the eye is due to the cornea. After the cornea, light enters the anterior chamber and is partially blocked by the pupil, which is the opening in the iris. Light entering through the iris is then focused by the crystalline lens in the eye, which is the only structure in the eye with significantly variable power. The crystalline lens is focused by a muscle attached around the periphery of the lens. The light then passes through the vitreous and focuses on the retina (if properly corrected). If the light does not focus onto the retina, then an uncorrected refractive condition exists.

Refractive conditions are most commonly treated with corrective lenses -- either spectacle lenses or contact lenses. The most common ones are near-sightedness (myopia), far-sightedness (hyperopia), astigmatism (when the eye is shaped like a football instead of like a basketball), and presbyopia (a condition caused by aging of the crystalline lens and leading to the need for reading glasses). Referring to Figure 2, in a "perfect" eye light from a distant object focuses directly onto the retina when the eye is relaxed or unfocused. In near-sightedness, distant light focuses in front of the retina, and requires a concave lens to bring the focus back onto the retina. In far-sightedness, distant light focuses behind the retina when the eye is relaxed, and requires a convex lens to bring the focus back onto the retina. In an astigmatic eye, the cornea or front surface of the eye is not spherical, and the power of the eye is different depending upon the plane in which the incident light approaches. A lens with different curvatures in different planes of rotation is required.