To assess the efficacy, safety and predictability of RK, the National Eye Institute, a branch of the National Institutes of Health, funded the Prospective Evaluation of Radial Keratotomy (PERK) study in 1980. From 1982 to 1983, 435 patients received RK in this study.
After five years, the PERK study results concluded that RK effectively reduced myopia, but that results varied among individuals. Sixty percent of the treated eyes had an uncorrected (without glasses or contacts) visual acuity of 20/20 or better, and 87% had 20/40 or better. Patients with a preoperative refraction of -2.00 diopters to -4.50 diopters achieved the best results.
In 1991, the PERK study conducted a ten year follow-up examination. The results indicated that 53% of the treated eyes had an uncorrected visual acuity of 20/20 or better, 85% had 20/40 or better, and 2% had an uncorrected visual acuity of 20/200 or worse.
Three percent of the patients in the PERK study lost 2 or more lines of best corrected vision. Best corrected vision is eyesight correctable to 20/20 with the aid of glasses or contacts. To lose one line of best corrected vision is to be only correctable to 20/25, and two lines to only 20/30.
The results of the ten year follow-up also indicated that 40% of the treated eyes had a gradual shift towards hyperopia, called the hyperopic shift. During the ten years following the initial operations, the percentage of undercorrected eyes decreased from 25% to 11% and the number of over corrected eyes increased from 9% to 30%. The duration of the hyperopic shift is unknown.
As a result of the ten year follow-up, the PERK study considers radial keratotomy to be “a reasonably safe and effective technique to improve distance vision.”
Pages: 1 2
