Algorithm for Correcting the Keratometric Error in the Estimation of the Corneal Power in Keratoconus Eyes after Accelerated Corneal Collagen Crosslinking

PURPOSE: To analyze the errors associated to corneal power calculation using the keratometric approach in keratoconus eyes after accelerated corneal collagen crosslinking (CXL) surgery and to obtain a model for the estimation of an adjusted corneal refractive index (n(k(adj))) minimizing such errors. METHODS: Potential differences (ΔP(c)) among keratometric (P(k)) and Gaussian corneal power (P(c)(Gauss)) were simulated. Three algorithms based on the use of n(k(adj)) for the estimation of an adjusted keratometric corneal power (P(k(adj))) were developed. The agreement between P(k(1.3375)) (keratometric power using the keratometric index of 1.3375), P(c)(Gauss), and P(kadj) was evaluated. The validity of the algorithm developed was investigated in 21 keratoconus eyes undergoing accelerated CXL. RESULTS: P (k(1.3375)) overestimated corneal power between 0.3 and 3.2 D in theoretical simulations and between 0.8 and 2.9 D in the clinical study (ΔP(c)). Three linear equations were defined for n(k(adj)) to be used for different ranges of r(1c). In the clinical study, differences between P(k(adj)) and P(c)(Gauss) did not exceed ±0.8 D n(k) = 1.3375. No statistically significant differences were found between P(k(adj)) and P(c)(Gauss) (p > 0.05) and P(k(1.3375)) and P(k(adj)) (p < 0.001). CONCLUSIONS: The use of the keratometric approach in keratoconus eyes after accelerated CXL can lead to significant clinical errors. These errors can be minimized with an adjusted keratometric approach.