Myopia and myopic astigmatism photorefractive keratectomy: applying an advanced multiple regression-derived nomogram

To evaluate a multiple regression-derived nomogram for myopia and myopic astigmatism photorefractive keratectomy (PRK).

Regression modeling derived a formula for spherocylindrical correction in wavefront-optimized PRK (nomogram II). Treatment outcomes between eyes with myopia and myopic astigmatism using the manufacturer's nomogram (nomogram I) in the years 2010-2013 were retrospectively compared with eyes treated using nomogram II in the years 2014-2015.

Overall 1100 eyes (of 561 patients) were operated using nomogram I and 791 eyes (of 406 patients) using nomogram II. Nomogram II achieved correction within ± 0.5 D of the attempted in 90% (95% CI 86.8-92.3%) of eyes with a spherical equivalent (SE) < |- 6|D, compared to 84% (95% CI 81.8-86.9%) in nomogram I. Overcorrection was reached in 14% (95% CI 10.1-18.3%) of eyes with SE ≥ |-6|D in nomogram II, compared to 22.6% (95% CI 18.1-27.2%) in nomogram I. Nomogram II achieved correction within ± 0.5 D of the attempted in 88.7% (95% CI 85.7-91.6%) of patients aged 18-23 years compared to 81.2% (95% CI 77.9-84.5%) in nomogram I; however, in 77% (95% CI 69.5-84.4%) versus 87.4% (95% CI 82.7-92.0%), respectively, among patients aged ≥ 30 years. In eyes with astigmatism ≥ 2 D, a postoperative astigmatism < 0.5 D was achieved in 89.4% (95% CI 83.0-95.7%) versus 72.9% (95% CI 64.3-81.5%), and a treatment efficacy index ≥ 0.9 was achieved in 100% versus 92.6% (95% CI 87.6-97.6%) with nomogram II versus nomogram I, respectively.

There were several clinically significant benefits of the advanced nomogram in wavefront-optimized myopia PRK. On the other hand, there was a trend of lower accuracy in the older age group, warranting a second iteration.