Total keratometry versus standard keratometry for intraocular lens power calculation in eyes with keratoconus.

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

SETTING

Asociación Para Evitar la Ceguera en México, Mexico City, Mexico.

DESIGN

Observational, retrospective, non-randomized, comparative study.

METHODS

Biometric data from IOL Master 700 and postoperative refraction were collected from patients with keratoconus who had undergone cataract surgery. Predicted refraction of each patient was calculated using K and TK with the following formulas: SRK/T, Barrett Universal II, Panacea, Kane, Kane keratoconus, and Barrett True-K keratoconus (predicted and measured posterior corneal astigmatism [PCA]). Refractive prediction error, mean absolute error, trimmed mean, median absolute error, standard deviation, and percentage of eyes within ± 0.50 D, ± 1.00 D, ± 1.50 D, ± 2.00, and > 2.00 D were determined.

RESULTS

55 keratoconic eyes of 40 patients were included. RPE in patients with keratoconus was < 1.00 D with all formulas. Barrett True-K keratoconus with predicted PCA registered the lowest MAE and MedAE. All formulas showed a discrete increase in myopic error percentage when calculations were performed using TK as opposed to K.

CONCLUSIONS

Barrett True-K for keratoconus showed the highest accuracy, closely followed by Kane KC. BTK KC pPCA or mPCA with standard keratometries could serve as the primary choice in eyes with keratoconus and steepness < 60 D. In the absence of keratoconus-modified formulas, TK input in conventional formulas improves the prediction outcome.