The cornea and lens combine to focus visual images on the back of the eye. When the overall shape of the eye is incorrect or when the curvature of the cornea is incorrect, the visual images are not in focus. The cornea accounts for approximately 2/3rds of the focusing power of the eye. By surgically changing the corneal curvature, most or all of the blur can be eliminated.

Laser In Situ Keratomileusis (LASIK) and Photo-Refractive Keratectomy (LASIK) are two surgical techniques which utilize lasers to reshape or change the curvature of the cornea.


LASIK had its origins about thirty years ago and was originally developed to treat patients who had very poor vision due to corneal disease. It has now evolved into a successful technique for correcting refractive errors. The current procedure, done on an outpatient basis, involves both the use of conventional and laser surgery to correct nearsightedness, farsightedness and astigmatism. LASIK can correct a much higher degree of nearsightedness with or without astigmatism than any other refractive procedure, with excellent results (95% of patients achieve 20/40 vision or better).

In performing LASIK, eye drop anesthetic is used to numb the eye. The surgeon then uses a special instrument to cut into and behind a layer of the cornea. A portion of the cornea is peeled back to create a flap and expose the inner portions of corneal tissue. The eye is then positioned under the excimer laser which has been computer programmed to remove microscopic amounts of the internal corneal tissue. Removal of the tissue changes the curvature of the cornea. If the patient is nearsighted, tissue closer to the central part of the cornea is removed to decrease the curvature or flatten the cornea. If a patient is farsighted, tissue in the peripheral part of the cornea is removed to increase the curvature of the cornea. To correct for astigmatism, selected tissue at certain angles is removed to insure that the cornea curves equally in all directions. After the laser has been used, the flap is returned to its original position. The corneal tissue has extraordinary natural bonding qualities that allow effective healing without the use of stitches.

Since only local anesthetic is used, patients remain awake during the procedure. The entire procedure takes only a few minutes. Improved vision is often possible on the day following the surgery. Eye drops and night protection are necessary for designated periods of time.

Advantages of LASIK include:

  • Faster healing time
  • Rapid visual recovery
  • Less risk of scarring
  • Less risk of corneal haze
  • Less post-op discomfort
  • The second eye can be done within a week
  • Treatment of a wider range of nearsightedness


Photo-Refractive Keratectomy, PRK is another method of surgically reshaping the cornea using the excimer laser. The difference between LASIK and PRK is that for PRK, the corneal flap is not created. That is, the outer layer of the cornea remains in place and the laser removes tissue directly from this outer layer. During LASIK , a part of the cornea is peeled back so that the laser removes tissue from the inner corneal layers. PRK is used for low to moderate amounts of nearsightedness.

Just as in LASIK, the laser treatment requires less than a minute. But unlike LASIK, the healing period time is longer. The correction for nearsightedness, farsightedness and astigmatism is the same as in LASIK. The corneal curvature is changed so that the visual images are properly focused on the back of the eye.

Patient Education Library reprinted with permission of Einstein Medical, Inc. (c) 2000