Preliminary validation of an optimized algorithm for intraocular lens power calculation in keratoconus

PURPOSE: This study aimed to evaluate the theoretical influence on intraocular lens power (P(IOL)) calculation of the use of keratometric approach for corneal power (P(c)) calculation in keratoconus and to develop and validate an algorithm preliminarily to minimize this influence. METHODS: P(c) was calculated theoretically with the classical keratometric approach, the Gaussian equation, and the keratometric approach using a variable keratometric index (n(kadj)) dependent on r(1c)(P(kadj)). Differences in P(IOL) calculations (ΔP(IOL)) using keratometric and Gaussian P(c) values were evaluated. Preliminary clinical validation of a P(IOL) algorithm using P(kadj) was performed in 13 keratoconus eyes. RESULTS: P(IOL) underestimation was present if P(c) was overestimated, and vice versa. Theoretical P(IOL) overestimation up to −5.6 D and −6.2 D using Le Grand and Gullstrand eye models was found for a keratometric index of 1.3375. If n(kadj) was used, maximal Δ P(IOL) was ±1.1 D, with most of the values ≤±0.6 D. Clinically, P(IOL) under- and over-estimations ranged from −1.1 to − 0.4 D. No statistically significant differences were found between P(IOL) obtained with P(kadj) and Gaussian equation (P > 0.05). CONCLUSION: The use of the keratometric P(c) for P(IOL) calculations in keratoconus can lead to significant errors that may be minimized using a P(kadj) approach.