Total Keratometry Versus Simulated Keratometry In Intraocular Lens Power Calculation In Eyes With Keratoconus

To describe the accuracy of monofocal intraocular lens power calculation in patients with keratoconus using total keratometry (TK) and simulated keratometry (K) with conventional and keratoconus-modified formulas.

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Biometry data from IOL Master 700 and postoperative refraction were collected from patients with keratoconus who had undergone cataract surgery. We calculated the predicted refractive error of each patient using TK and K with the following formulas: SRK-II, SRK-T, Barrett Universal II, unmodified Kane, Kane keratoconus, Barrett True-K keratoconus (predicted and measured PCA), and Panacea. Refractive prediction error (RPE), mean absolute error (MAE), median absolute error (MedAE), standard deviation (STDEV), and percentage of eyes within ±0.50 D, ±1.00 D, ±1.50 D, ±2.00, and >2.00 D was determined.

55 keratoconic eyes of 40 patients were included. Kane keratoconus showed the lowest RPE (0.04) when TK was used, whereas Barrett True-K keratoconus with predicted PCA had the lowest RPE (0.09) in the K group. Barrett True-K keratoconus with predicted PCA registered the lowest MAE and MedAE in both TK and K groups. All formulas showed a discrete increase in myopic error percentage when calculations were performed using TK as opposed to K.

RPE in patients with keratoconus was <1.00 D with all formulas, except SRK-T, when calculated using TK. Barrett True-K keratoconus, Kane keratoconus, and Panacea offered the highest accuracy, though an overall tendency towards hyperopic error was noted.