Possible Side Effects
If the patient's vision is overcorrected during surgery, postsurgical flattening causes progressive loss of refractive power (ability to bend and focus light rays). Consequently, instead of being myopic (light rays are focused in front of the retina), the eye becomes hyperopic, or farsighted (i.e., light rays are focused in back of the retina).
As the number of RK patients increased, surgeons encountered an increasing number of potential side effects. Some patients complained of discomfort when in bright light, persistent glare, or disorienting starlike bursts of light when approaching a light at night (e.g., an oncoming vehicle's headlights). Moreover, some patients also lost their best correct visual acuity, i.e., their vision was not able to be corrected as well as before RK with properly prescribed glasses or contact lenses. Others suffered infections from microorganisms that infected the incisions.
A National Eye Institute study, called Prospective Evaluation of Radial Keratotomy (PERK), evaluated 693 patients 10 years after RK procedures were performed in 1982 and 1983 to reduce nearsightedness. Seventy percent did not require corrective lenses for long distance; 85% were corrected to 20/40 or better; 53% to 20/20 or better; and 43% continued to change toward farsightedness; and a significant decrease in vision, even with glasses, occurred in 3% of patients.
In the 1990s, a newer technique, called Photoreactive Keratectomy (PKR) utilized a type of laser called an excimer laser to decrease nearsightedness. This laser removes a very precise amount of tissue off the center of the cornea using a "cold" ultraviolet laser, changing the corneal shape to bring the focal point closer to the retina. By the late 1990s, a third correctional device, called the LASIK (LAser in SItu Keratomileusis), was being used. It combines the excimer laser and a microkeratome to also reduce nearsightedness. Although approved by the FDA independently, their combined use is not yet approved. However, in this procedure, the eye is anesthetized and a suction ring centered over the cornea to stabilize the eye. This ring also and provides "guide tracks" for the microkeratome, a very precise instrument that "shaves" a micro-thin partial flap off the center of the cornea, leaving it attached at one side like a hinge while exposing the middle portion of the cornea. The excimer laser is then used to remove tissue and reshape the center of the cornea. The flap is replaced and conforms to the flatter, reshaped cornea.
See also Vision disorders.