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‘Encouraging' 10-year data shows PRK is a safe procedure A 10-year follow-up study of PRK performed with a first generation excimer laser confirms the long-term efficacy and safety of the surgery, but questions about stability remain, French researchers reported at the annual ASCRS Symposium on Cataract, IOL and Refractive Surgery. The study included 100 consecutive eyes in 76 patients who underwent PRK between July 1991 and December 1992. Follow-up data was available on 100 eyes at one year, 77 eyes at five years and 52 eyes in 35 patients at 10 years. The myopia of patients in the study ranged from -1.0 D to -12.0 D before surgery. PRK was performed by the same surgeon using a Meditec MEL 60 laser at 20 Hz with a 5.0mm optical zone. Uncorrected visual acuity was 20/40 or greater in 73% of patients, while 37% had UCVA of 20/20 or greater at 10 years. No eye lost more than two lines of visual acuity in the 10-year follow-up period, reported Barbara Ameline-Chalumeau MD. After 10 years, almost 70% of patients maintained emmetropia within 1.0 D, compared with 84% at one year. Only 48% of patients were emmetropic within 0.5 D at 10 years, compared with 65% at one year.The researchers found that myopic regression, which can reduce uncorrected visual acuity, occurred between the first and fifth year after surgery, but not between the fifth and tenth year."Between the one and five-year time points there was a statistically significant myopic shift. Changes between the fifth and tenth year were not statistically significant," Dr Ameline-Chalumeau said. The researchers divided the patients into three groups before surgery - low (-1.0 D to -2.75 D), moderate (-3.0 D to -5.75 D) and high myopes (-6.0 D to 10.25 D). The initial spherical equivalent (SE) of the three groups ranged from -2.04 in the low myope group to -7.61 in the high myope group. After PRK, the researchers found that mean SE changed significantly between the first and fifth year in all three groups. In the three groups, the mean myopic shift ranged from -.18 D to -.39 D from the first to the fifth year. In low myopes, the SE at one year was -0.09, in moderate myopes -0.44, and in high myopes -1.37. However 10 years after surgery, the mean SE was -.38 in low myopes, -.81 in moderate myopes and -1.63 in high myopes. "Although the regression seems more important in the high myopia group, we could not demonstrate any statistical difference among the three regression slopes," she commented. Dr Ameline-Chalumeau noted that previous studies have reported stability as soon as the first or second year after PRK. At the same time, contradictory studies have shown myopic shift in PRK patients up to five years after surgery. Also, long-term modifications of corneal morphology have been documented by in vivo confocal microscopy five years after PRK. "Whether or not the myopic shift seen in our study is a natural evolution of refraction or a delayed healing process remains the main question. Although patients had stable refraction two years before surgery we cannot eliminate the spontaneous evolution of myopia," she said. Though the study matched the age and sex data, the researchers did not find any factors that accounted for the myopic regression between the first and fifth year. Most patients were treated bilaterally, making assessment of the reasons for the myopic regression all but impossible. "My personal feeling is that most of the change in refraction is caused by natural evolution, but it's difficult to demonstrate," she said. The researchers acknowledged the limitations of the study. 48% of patients were lost to follow-up, and both eyes were analysed in 50% of patients. There was also no objective measurement of corneal opacities or evaluation of vision quality. However, the study found that all haze had disappeared among patients after five years. Dr Ameline-Chalumeau said the results of the study were "encouraging". While the study used a 5.0mm optical zone, larger optical zones, better ablation profiles and superior delivery systems can only enhance the results. Long-term stability and predictability of PRK will no doubt improve, she predicted. Barbara Ameline-Chalumeau MD
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