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Differences in total corneal astigmatism in the healthy eye calculated using the keratometric and power vector methods, and a new approach for astigmatic analysis

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Session Details

Session Title: Presented Poster Session: IOL Power Calculation/Paediatric

Venue: Poster Village: Pod 1

First Author: : D.Piñero SPAIN

Co Author(s): :    M. Caballero   R. Soto-Negro   D. de Fez   V. Camps   M. Ramón  

Abstract Details


To evaluate and compare the total corneal astigmatism value obtained in healthy eyes using three different approaches for its calculation: keratometric approach (K), power vector calculation (PV) and a new method for astigmatic analysis (N) considering the contribution of corneal thickness


Department of Ophthalmology (OFTALMAR). Vithas Medimar International Hospital, Alicante, Spain


Retrospective study including a total of 317 healthy eyes from 205 patients (age, 21-52 years). In all cases, a complete corneal analysis was performed with the Scheimpflug imaging system Pentacam (Oculus). With the information obtained, the K and PV methods were used to obtain the total corneal astigmatism. Likewise, a new method for astigmatic analysis was proposed consisting on the calculation of anterior and posterior corneal power meridian by meridian (2.5º intervals) and the calculation of the total corneal power in each meridian with the Gaussian equation (considering corneal thickness), detecting the principal meridians (highest and lowest powers)


Mean magnitude of total astigmatism was 1.31±1.04, 1.06±0.87 and 1.06±0.88 D with K, PV and N methods (p<0.001), and mean axis was 92.1±72.4, 94.6±68.6, and 94.6±68.6º, respectively (p<0.001). Differences between PV and N methods in magnitude (p=0.162) and axis (p=0.728) were not statistically significant. The Bland and Altman analysis revealed that K was not interchangeable with PV and N values, with large limits of agreement associated (LoA). However, N and PV calculations could be used interchangeably in terms of magnitude (LoA, -0.15 to 0.16 D) and axis (LoA, -0.80 to 0.81º)


The keratometric approach not considering the posterior corneal surface astigmatism can lead to an erroneous estimation of total corneal astigmatism. Power vector method is useful for obtaining an accurate estimation of total corneal astigmatism in healthy eyes as the contribution of the corneal thickness factor is minimal. Future comparative studies between K, PV and N methods should be performed in thin corneas, such as keratoconus

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