“There seems to be a discrepancy between the regression associated with PRK at -1.05D and that of LASIK at -1.65D, considering that LASIK refractive outcomes

TEN years after some of the first photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK) surgeries, patients are showing stable corneas and visual results, a Spanish study confirms. Jorge L Alio MD, PhD,Vissum Instituto Oftalmologico de Alicante,Alicante, Spain, reviewed the long-term results of 200 eyes that had undergone laser refractive surgery. The eyes were treated for up to -10 D myopia or myopic astigmatism. “10 years after surgery, LASIK and PRK are both good refractive procedures, with a trend towards greater myopic regression for LASIK.At the same time, LASIK had somewhat superior refractive results, due to the better outcomes of the cylinder correction,” he told a session of the XXIVth Congress of the ESCRS. Of the 200 eyes included in Dr Alio's investigation, 100 eyes underwent PRK and the other 100 underwent LASIK surgery with a Visx 20/20 excimer laser. He followed the patients for 10 years after surgery, measuring corneal power, uncorrected and corrected visual acuities, and refractive error. Ten years postoperatively, the mean spherical equivalent was -0.88 ± 1.4 D and -0.66 ± 1.4 D for eyes operated by PRK and LASIK, respectively. Mean pre-operative values were -7.5 ± 1.11 D for the PRK group and -8.7 ± 1.15 D for the LASIK group. The mean safety and efficacy indices in the PRK group were 1.04 and 0.81, respectively, and 1.16 and 0.82 for the LASIK group. Corneal keratometry measurements averaged 38.69 ± 2.3 D in PRK patients and 38.55 ± 2.4 D in LASIK patients.The changes in corneal keratometry and topographical cylinder over the 10 years since surgery were minimal, Dr Alio emphasised. Myopic regression was -1.05 D for PRK and -1.65 D for LASIK over the 10-year period.The difference in regression was at the limit of statistical significance (p = 0.051), Dr Alio noted. Dr Alio explained that not all of the 10year results comparing LASIK and PRK had statistical significance. For instance, differences in uncorrected acuity showed a significance of p = 0.052, ie, not significant. The differences in best-corrected acuity and myopic regression in the two treatment groups were also statistically insignificant. Conversely, the differences in topographical cylinder and spherical equivalent were statistically significant at p=0.017 and p= 0.022, with better results seen with LASIK in both cases. Noel Alpins MD, the session moderator, wondered how the LASIK results could show a higher incidence of regression while also resulting in better refractive correction than PRK. “There seems to be a discrepancy between the regression associated with PRK at -1.05D and that of LASIK at -1.65D, considering that LASIK refractive outcomes were better.According to the study data, over time, the crossover in refractive outcomes efficacy seemed to occur at about two years postop, and yet the average topographic and keratometric values were fairly equivalent during this period. Is this due to a real phenomenon or was there a difference in follow-up frequencies between the two groups?” Dr Alio explained that the LASIK group had an overall higher pre-operative spherical power, with about the same cylinder as the PRK group.This group was therefore prone to more regression at the higher myopic corrections performed, he said. He maintained that although he had no data to support his hypothesis, this was likely to be the best explanation. He said that vital factors such as lasers and microkeratomes have improved over the 10 years of the analysis and that suboptimal microkeratome cutting quality compared to today's quality standards needed to be taken into account. Dr Alio observed that no patient had undergone re-treatment in this investigation and that his data represented the untouched evolution of eyes operated for myopia. He felt that based on his results, any patient eligible for both PRK and LASIK with visual acuity of -6 D would be better served with LASIK than PRK. Guy Kezirian MD observed that 10-year data was crucial to provide refractive eye surgeons with a much-needed long-term overview of refractive procedures. He felt, nonetheless, that a paired-eye analysis, in which the investigator looks at the change in each eye at separate intervals, would be helpful. Following the same eye, the investigator analyses the statistics on the changes in a given eye, rather than just looking at the population means, allowing him to highlight the changes in each eye at a given interval. “You can sometimes more sensitively pick up trends by looking at changes in a given eye from interval to interval and then doing statistics on the changes observed in that period,” he said. Dr Alio agreed that although this particular investigation did not include paired-eye examinations, the results would have increased the perspective of his results. In this study what was interesting was that the eyes are untouched by any retreatments, he explained. Moreover, the comparison is of the topographical results, which clearly revealed that both refractive procedures showed good stability and good results after 10 years.