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Algorithm for correcting keratometric error in the estimation of corneal power in eyes with previous myopic laser refractive surgery

Poster Details

First Author: D.Piñero Llorens SPAIN

Co Author(s):    V. Camps   V. Mateo   R. Pérez-Cambrodí   F. Blanes-Mompó   P. Ruiz-Fortes   D. Ribera-Vicent

Abstract Details


To calculate theoretically the errors in the estimation of corneal power when using a keratometric index (nk) in eyes with previous laser refractive surgery for the correction of myopia, as well as to define and validate clinically an algorithm for minimizing such errors


Oftalmar, Department of Ophthalmology Medimar International Hospital, Alicante, Spain


Differences among corneal power estimation by using the classical nk and by using the Gaussian equation in eyes with previous laser myopic refractive surgery were simulated and evaluated theoretically. Additionally, an adjusted keratometric index (nkadj) model dependent on r1c was developed for minimizing these differences. The model was validated clinically using retrospectively the data from 32 myopic eyes (range, -1.00 to -6.00D) that had undergone LASIK using a solid-state laser platform. Agreement between Gaussian (PGauss) and adjusted keratometric (Pkadj) corneal powers in such eyes was evaluated


Overestimations of corneal power up to 3.5 D were found as possible for nk=1.3375 according to our simulations. The nk value to avoid the keratometric error ranged between 1.2984 and 1.3297. The following nkadj models were obtained: nkadj=-0.0064286r1c+1.37688 (Gullstrand eye model) and nkadj= -0.0063804r1c+1.37806 (Le Grand). Mean difference between Pkadj and PGauss was 0.00 D, with limits of agreement of -0.45 and +0.46 D. This difference correlated significantly with posterior corneal radius (r=-0.94, P<0.01)


The use of a single of nk for estimating the corneal power in eyes with previous laser myopic refractive surgery can lead to significant errors. These errors can be minimized by using a variable nk dependent on r1c

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