Myopia and myopic astigmatism photorefractive keratectomy: applying an advanced multiple regression-derived nomogram
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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.
KeywordsNomogram PRK Refractive surgery Regression analysis Accuracy Outcome
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the Barzilai Medical Center institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study, formal consent is not required.
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