Abstract
PURPOSE: to study the effect of keratoconus severity on the accuracy of intraocular lens power calculation using newer keratoconus (KC) specific formulas. METHODS: This was a retrospective case series that included 99 eyes from 99 patients. The included patients were further subdivided into 3 groups according to keratoconus severity. The results of various IOL power calculation formulas were analyzed in this study. Two KC specific formulas were employed: Barrett True K KC and Kane KC. Additionally, the following formulas were utilized: Barrett Universal II (BUII), EVO 2.0, Hoffer QST, Kane, and PEARL-DGS. RESULTS: The Kane KC was the only formula to show a myopic mean prediction error (- 0.76 ± 1.06 D). BUII and Barrett True K KC formulas showed the least mean and median absolute errors. The median absolute error (MedAE) for BUII and Barrett True K KC was 0.34 and 0.35 D respectively. BUII and Barrett True K KC formulas had the highest cases within ± 0.25 D of the intended refraction (42.42% and 39.39%, respectively). In severe KC eyes, the MedAE for Barrett True K KC and BUII formulas was 0.56 and 0.46 D respectively. In severe KC eyes, Barrett True K KC and BUII formulas showed the highest cases within ± 0.25 D of the intended refraction (27.27% and 27.27%, respectively). CONCLUSION: most non KC specific IOL power calculation formulas perform in an acceptable way in mild KC eyes. In moderate and severe KC eyes, the KC specific formulas perform better than the standard formulas. Barrett True K KC formula performed better than Kane KC in moderate and severe KC eyes. BUII formula was the best performing non KC specific formula in moderate and severe KC eyes.