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Estimation of the central corneal power in keratoconus: theoretical and clinical assessment of the error of the keratometric approach

Poster Details

First Author: D.Pinero SPAIN

Co Author(s):    V. Camps   E. Caravaca-Arens   R. PĂ©rez-CambrodĂ­   A. Artola     

Abstract Details


To analyze theoretically the errors in central corneal power calculation in keratoconus eyes when a keratometric index (nk) is used as well as to confirm clinically the errors induced by this approach.


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


Differences (APc) among central corneal power estimation with the classical nk (Pk) and with the Gaussian equation (PcGauss) in eyes with keratoconus were simulated and evaluated theoretically, considering the potential range of variation of the central radius of curvature of the anterior (r1c) and posterior (r2c) corneal surfaces. Furthermore, these differences were also studied in a clinical sample including 44 keratoconic eyes (27 patients, age range: 14 to 73 years). The clinical agreement between Pk and PcGauss(true net power) obtained with a Scheimpflug photography-based topographer was evaluated in such eyes.


For nk=1.3375, an overestimation was observed in most of cases in the theoretical simulations, with APc ranging from an underestimation of -0.1 D (r1c=7.9 mm and r2c=8.2 mm) to an overestimation of 4.3 D (r1c=4.7 mm and r2c=3.1 mm). Clinically, Pk always overestimated the PcGauss given by the topography system in a range between 0.5 and 2.5 D (p<0.01). Mean clinical APc was 1.48 D, with limits of agreement of 0.71 and 2.25 D. A very strong statistically significant correlation was found between APc and r2c (r=-0.93, p<0.01).


The use of a single value for nk for the calculation of corneal power is imprecise in keratoconus and can lead to significant clinical errors. Future studies should evaluate the impact of such errors on IOL power calculations. FINANCIAL INTEREST: NONE

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