Accuracy of Intraocular Lens Formulas in Eyes With Keratoconus.

Purpose: To evaluate the refractive accuracy of current intraocular lens (IOL) formulas in eyes with keratoconus.

Design: Retrospective case series.

Methods: Preoperative optical biometry, Pentacam topography, and postoperative outcomes were collected from eyes with keratoconus that had uncomplicated cataract surgery between 2014 and 2018 at a single institution. Exclusion criteria include postoperative best-corrected spectacle visual acuity worse than 20/40, multifocal lens, prior ophthalmic surgeries, and prior ocular trauma. The Hoffer Q, SRK/T, Holladay I, Holladay II, Haigis, and Barrett Universal II formulas were analyzed in each eye stratified by keratoconus severity.

Results: A total of 73 eyes were included. All formulas had a positive mean predicted error ranging from 0.10 to 4.38 diopters (D). The Barrett Universal II formula had the lowest median absolute error for stage I (n = 46, 0.445 D) and II (n = 22, 0.445 D) eyes, and the highest percentage of eyes with predicted error within ±0.50 D for both stage I (52%) and II (50%) eyes. In stage III eyes (n = 5), the Haigis formula had the lowest median predicated error (1.90 D) and the highest percentage of eyes with predicted error within ±0.50 D (40%). Corneal power measured by optical biometers was higher than measurements by Pentacam keratometry.

Conclusions: All formulas tend to have a hyperopic surprise. The Barrett Universal II formula was the most accurate for mild to moderate disease. Pentacam keratometry may help avoid hyperopic outcomes.