Vecto-keratometry: determination of anterior corneal astigmatism in manual keratometers using power vectors

A new keratometric routine that employs power vector management for manual keratometers is described. This study evaluates the agreement of the new proposed keratometric technique with the classical one.

The applicability of a new keratometric routine was verified using Helmholtz's and Javal's keratometers. Results were obtained by two different and well-trained examiners over two different samples, one including 65 and the other 74 eyes, respectively. Both conventional keratometry and the newly proposed routine (named vecto-keratometry) were used in each eye to obtain the results. The clinical agreement between the methods was evaluated using Bland-Altman and Passing-Bablok analysis.

For Helmholtz's keratometer, Bland-Altman plots showed good agreement between methods for both astigmatic components being J₀ = 0.04 ± 0.20 D and J₄₅ = -0.07 ± 0.17 D. For Javal's keratometer, Passing-Bablok regression test determined regression line for J₀ difference as y₀ = 1.03, confidence interval: [0.98, 1.10] and regression line for J₄₅ difference as y₄₅ = 0.97, confidence interval: [0.83, 1.12].

Vecto-keratometry provides accurate clinical results. It has been demonstrated that there are no significant differences between methods in any of the power vector astigmatic components; thus, both methods can be applied interchangeably.