Radial keratotomy (RK) is now largely considered an obsolete procedure, but it did play an important role in the history of refractive surgery and was the primary procedure for treating patients with −1.00 to −4.00 D of myopia. The excimer laser was originally applied to the cornea to produce more accurate RK incisions, not for surface ablation or laser in situ keratomileusis (LASIK), for which the excimer laser is now used. Radial keratotomy differs from surface ablation and LASIK in that it does not involve removal of tissue from the central cornea.
To evaluate the safety and efficacy of RK, the Prospective Evaluation of Radial Keratotomy (PERK) study was undertaken in 1982 and 1983 for patients with myopia from –2.00 to –8.75 D (mean: –3.875 D). The sole surgical variable was the diameter of the central optical clear zone (3.00, 3.50, or 4.00 mm), based on the level of preoperative myopia. It was later found that the older the patient, the greater the effect achieved with the same surgical technique. In the PERK study, 8 radial incisions were used for all patients; repeat surgery, if necessary, involved an additional 8 incisions. Ten years after the procedure, 53% of the 435 study patients had 20/20 or better uncorrected visual acuity (UCVA) and 85% were 20/40 or better. Of the patients who had bilateral surgery, only 30% reported the use of spectacles or contact lenses for distance refractive correction at 10 years. Complications related to the procedure included loss of best-corrected visual acuity (BCVA; 3%), delayed bacterial keratitis, corneal scarring, irregular astigmatism, and epithelial erosions.
The most important finding in the 10-year PERK study was the continuing long-term instability of the procedure. A hyperopic shift of 1.00 D or greater was found in 43% of eyes between 6 months and 10 years postoperatively. There was an association between length of the incision and hyperopic shift, particularly if the incisions extended into the limbus.
, LynnMJ, McDonnellPJ; PERK Study Group. Results of the Prospective Evaluation of Radial Keratotomy (PERK) study 10 years after surgery.1994;112(10):1298–1308.