Reported January 2007

BACKGROUND: Ophthalmologists at the University of Rochester Medical Center in New York have developed a formula that slashes by nearly two-thirds the likelihood that patients will need repeat visits to an eye surgeon to adjust their vision after their initial LASIK visit. That's because the formula makes it more likely that surgeons will get it right the first time. The new software controls how the laser beam used in the surgery travels around the surface of the cornea during the procedure enabling the surgeon to sculpt the cornea into just the right shape so that it produces as flawless an image as possible. Everyone's eyes are slightly different. By taking into account the unique anomalies in each person's eye, the formula predicts which patients are most likely to be slightly far-sighted after a LASIK procedure, and adjusts the laser to avoid that outcome. This reduces the need for repeat treatments in patients from about 8 percent to 3 percent.

LASING A PATH: Laser eye surgery uses a pulsed, tightly focused beam of light to vaporize a tiny portion of the cornea to reshape it. The surgeon creates a thin, circular flap in the cornea with a laser, folds it back out of the way, then removes some of the cornea tissue underneath, also by laser. The flap is then laid back into place over the area where the tissue was removed. By controlling the size, position and number of laser pulses, the surgeon can precisely control how much of the cornea is removed. Reshaping the cornea changes the focal point of the eye, resulting in corrected vision. A LASIK procedure generally lasts 15 seconds to 60 seconds, during which time the laser beam hits the cornea 50-times-per-second. So the timing and aim must be as precise as possible.

HOW LASERS WORK: "Laser" is an acronym for Light Amplification by Stimulated Emission of Radiation. It describes any device that creates and amplifies a narrow, focused beam of light whose photons are all traveling in the same direction, rather than emitting every which way at once. Laser light contains only one specific color, or wavelength. Lasers can be configured to emit many different colors in the spectrum, but each laser can emit only that one color. Because every photon is traveling in the same direction, the light is tightly focused into a concentrated beam, unlike the light emitted from a flashlight, where the atoms release their photons randomly in all directions. There are many different types of laser, but all of them have a cavity containing a "lasing" medium: either a crystal such as ruby or garnet, or a gas or liquid. There are two mirrors on either end of the cavity, one of which is half-silvered, meaning that it will reflect some light and let some light through. (The light that passes through is the emitted laser light.) In a laser, the atoms or molecules of the lasing medium are "pumped" by applying intense flashes of light or electricity. The end result is a sudden burst of light as all the atoms discharge in a rapid chain reaction.

The American Association of Physicists in Medicine contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

Scott MacRae M.D.
Department of Ophthalmology
University of Rochester
100 Meridian Ctr. #125
Rochester, NY 14618
(585) 273-2020
Scott_MacRae@URMC.Rochester.edu

Ben Stein
American Institute of Physics
(for the American Association of Physicists in Medicine)
(301) 209-3088
bstein@aip.org