A new laser which zaps microscopic amounts of tissue and reshapes the cornea will now allow eye specialists to fix a vision disorder that distorts the vision of more than 50 million people in the US.

The special excimer laser, which has been used by UCSF opthalmologists to correct nearsightedness, was approved Friday by the Food and Drug Administration to also treat astigmatism.

The procedure, photoastigmatic refractive keratectomy (PARK), allows UCSF cornea specialists to use an excimer laser to reshape the curvature of the cornea--the transparent window of the eye that covers the iris and the pupil and that admits light into the eye's interior--to correct astigmatism.
The excimer laser--manufactured by VISX Inc. of Santa Clara, Calif.--was approved in the spring of 1996 to treat persons with mild to moderate degrees of nearsightedness without astigmatism, and is now the first to receive FDA approval for treatment for both disorders.

"PARK offers hope of better vision without corrective lenses for at least two-thirds of the nearsighted Americans who also have astigmatism," says David Hwang, MD, UCSF associate professor of ophthalmology and co-director of the UCSF Vision Correction Center.

"By allowing treatment of both nearsightedness and astigmatism, the newly approved outpatient procedure more than doubles the number of individuals who now qualify for laser vision correction."

During the procedure, the excimer laser removes microscopic amounts of tissue from the surface of the cornea, making the central zone flatter. The flattened cornea is then able to focus light more directly on the retina, thereby reducing astigmatism and nearsightedness. Typically the entire treatment lasts less than 15 minutes and the excimer laser beam is used on the eye for less than a minute.

The excimer laser is unique because it emits a cold, or non-thermal, light beam. "It is ideal for corneal surgery because it eliminates the possibility of heat damage to surrounding tissue," says Richard Abbott, MD, UCSF professor of ophthalmology and co-director of the UCSF Vision Correction Center.

In astigmatism, the cornea is warped and curves more in one direction than another, like a football, which causes light to focus on two separate points in the eye, creating a distorted image in both near and distant vision.

Symptoms range from visual discomfort in mild cases, to severe blurring and distortion similar to a reflection in a fun-house mirror, where objects appear too tall, too wide, or too thin.

A normal cornea is round, like a basketball, and in normal vision focuses light rays directly onto the retina. Nearsighted vision is caused by a steeper curvature in the cornea, forcing the light rays to focus in front of the retina. Farsighted individuals have flatter corneas, which focus the light rays behind the retina.

Alternate treatments for astigmatism include certain kinds of contact lenses or eyeglasses for mild forms of the disorder, as well as astigmatic keratotomy--a surgical procedure in which spokelike cuts are made on the peripheral area to flatten the cornea.

For more information on treatments or clinical studies to correct astigmatism and nearsightedness, interested persons sould call 476-5021.

By Rebecca Higbee

1st appeared 4/28/97