Clinical Results of Photorefractive Keratectomy for Undercorrected Myopia after Radial Keratotomy

We report clinical results of 13 myopic patients(18 eyes), which remained undercorrected following radial keratotomy and then underwent photo refractive keratectomy(PRK) with an excimer laser(193 nm) to correct the residual myopia, with follow up of 1 year. Patient's mean age was 26 years. The time interval between radial keratotomy and PRK ranged 12 to 98 months(mean 40 months); group I(14 eyes) 6 diopter. At one year after PRK, uncorrected visual acuity was 20/25 or more in 15 eyes(83%). Mean manifest refractive error changed from -3.41 +/- 1.97D preoperatively to -0.91 +/- 0.41D after PRK in group I and fron -7.44 +/- 0.61D to -1.88 +/- 0.97 in group II. The mean keratometric power changed from 40.38D preoperatively to 38.32D after PRK in group I and from 42.93D to 38.56D in group II. Most common complaints were halo phenomenon and decreased vision at night. Persistent comeal haze(grade 2) was noted only in one eye at 3 months after PRK, but reduced to trace at 1 year. No other significant complications occurred. Therefore, excimer laser PRK appears to be an available method to correct residual myopia after radial keratotomy.

Corneal Topographic Diagnosis of Early Keratoconus and Observation of Corneal Change after Excimer Laser Photorefractive Keratectomy

We performed penetrating keratoplasty on the 40 eyes of 40 patients from Jan. 1991 through Dec. 1993, whose diagnosis was keratoconus. Among them, the opposite eyes of 5 patients had no keratoconus signs on the slit lamp biomicroscopic examination and keratometry reading. We performed computerassisted corneal topography on the 5 eyes and then they were classified as group I. We performed computer-assisted corneal topography on the 324 eyes of 324 patients. who visited our hospital to receive excimer laser photorefractive keratectomy(PRK). Among them, 7 eyes of 4 patients, which were suspected to be early keratoconus, were classified as group II. There were no signs of keratoconus by slit lamp examination and keratometry reading. Keratometry reading was 44.82D in the group I and 43.52D in the group II. Subtle mire distorsion of photokeratoscope was seen in the 1 eye of group I and 2 eyes of guoup II, but remaining 9 eyes were normal. We could not find keratoconus signs in the conventional examination such as above but on the corneal topography 12 eyes revealed cone-shaped corneal distorsion out of the corneal center. Two eyes in the group II were suspected to be early keratoconus in the corneal topographic examination, therefore we recommended them not to receive excimer laser PRK. But they received excimer laser PRK in the other hospital. They revisited our hospital due to progressively decreased visual acuity after excimer laser PRK. On the topography, 2nd and 12th months after PRK. corneal refractive power returned similarly to pre-PRK state. Therefore, computer-assisted corneal topography is a useful method in detecting corneal change in the early keratoconus stage. Performing PRK on the eye, suspected to be keratoconus, is unreasonable because corneal power is willing to return to pre-PRK state.