Accuracy Of Intraocular Lens Calculations In Eyes With Keratoconus

To compare the accuracy of commonly used IOL formulas and keratoconus-adjusted IOL formulas in keratoconic eyes undergoing cataract surgery. 

Multicenter (Shaare Zedek Medical Center, Jerusalem, Israel and University Eye Clinic, Maastricht, the Netherlands)

Eyes with stable keratoconus undergoing cataract surgery between August 2012 and April 2021 were included. The prediction error (PE) was calculated for the following formulas: SRK/T, Barrett Universal II (BUII), Barrett True-K for keratoconus with either predicted or measured posterior corneal astigmatism (True-K_KCN_P, True-K_KCN_M), Kane, and Kane adjusted for keratoconus (Kane_KCN). Primary outcomes were mean error (ME), mean absolute error (MAE), and percentage of eyes with PE ±0.25 D, ±0.50 D, and ±1.00 D. Subgroup analyses were performed based on the severity of the keratoconus.

A total of 57 eyes were included. Thirty-six eyes were categorized as stage I, 17 as stage II and 4 as stage III. ME did not differ statistically from zero for SRK/T, True-K_KCN_P, True-K_KCN_M, and Kane_KCN formula (range 0.09 to 0.22). ME using the BUII and Kane did differ statistically from zero (0.60±0.71 D and 0.60±0.77 D). The MAE of True-K_KCN_P (0.43±0.42 D) and True-K_KCN_M (0.44±0.38 D) were significantly different from BUII (0.72±0.58 D) and Kane formula (0.74±0.63 D) (p<0.001). The True-K_KCN_P had 88% of the eyes within a PE of 1.00D, which was significantly more than the Kane formula (68%) (p=0.004). True-K_KCN_M had 90% of eyes within a PE of 1.00D, which was significantly more than BUII (75%) and Kane (p=0.008 and p=0.002).

IOL calculation in eyes with keratoconus is challenging. In our study, keratoconus-adjusted IOL formulas, especially those with predicted and measured posterior corneal astigmatism, tend to result in a lower mean prediction error in eyes with keratoconus than conventional IOL formulas, except for the SRK/T.