Procedures like RK (radial keratotomy) and AK (astigmatic keratotomy) have been performed since the early 1970's to improve vision due to nearsightedness (myopia), farsightedness (hyperopia) and astigmatism. Called refractive surgery, these techniques have corrected or improved the vision of hundreds of thousands of people. Studies show that over 95% of patients that have refractive surgery are able to pass a standard driver's license eye exam (20/40 visual acuity or better) without wearing eye glasses.
How it Works
Refractive surgery techniques change the shape of the cornea of the eye so images are focused correctly at the back of the eye. In nearsighted people, for example, the curvature of the cornea is too steep or the eye is too long, causing light rays to focus in front of the retina on the back of the eye (see diagram). Surgery techniques for nearsightedness reduce the curvature of the cornea and allow distant images to focus.
With the advent of the laser for refractive surgery (photo-refractive keratectomy or PRK), a new era in eye care is unfolding. It has been found that the Excimer Laser procedure combined with the creation of a corneal flap (Lamellar Keratoplasty or LK) is an excellent technique for reshaping the surface of the cornea to correct nearsightedness and astigmatism. The combination of both procedures is called Laser Assisted In-Situ Keratomileusis (LASIK) and offers the accuracy of refractive lasers with the benefits of the LK procedure's speedy recovery.
After extensive pre-surgery testing, a computer is programmed by the doctor for each person's own correction factors. Next, a thin flap of tissue is created on the cornea. The flap is laid back, remaining attached to the cornea at one end. In treating myopia, as shown here, the laser segment of the procedure starts with a narrow diameter beam. As the laser beam expands, a tiny lens shaped disc is created. The focal point of the beam only penetrates the cornea about two thousandths of an inch (about half the thickness of a human hair). Only a small area in the center of the cornea is treated, essentially producing a concave lens over the visual axis. Finally, the corneal flap is replaced (without stitches) and the LASIK procedure is complete.
The LASIK procedure begins with the patient on their back. After the creation of a thin flap, a narrow laser beam is first applied. As the beam widens a concave disc is created on the cornea. The flap is then put back into its original position.
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