We measured angle lambda in normal and exotropic patients using Pentacam HR (Oculus, Wetzler, Germany). The relationship between angle lambda and refractive error was analyzed in the present study.

From December, 2013 to August, 2014, 135 eyes of 135 individuals under 16 years of age were enrolled in this study. Pentacam measures a distance between the center of the pupil and the corneal reflex point. The distance was converted to the angle lambda using the second law of cosines. All statistical analyses were performed using SPSS for Windows, version 21.0 (SPSS Inc, Chicago, IL, USA). The differences among the groups when measuring angle lambda were calculated using independent t -test, Mann-Whitney test and analysis of variance (ANOVA). Pearson's correlation test was used to analyze the correlation among the variables.

The mean age was 7.60 ± 3.68 years. Mean angle lambda values of the normal and exotropia groups were 4.41 ± 2.23° and 4.92 ± 2.58°, respectively. To evaluate the association of angle lambda and refraction measures, individuals were further classified according to the degree of myopia and hyperopia. The angle lambda values in the 3 groups according to refraction status (myopic, emmetropic and hyperopic) were 3.95 ± 2.16°, 4.84 ± 2.62° and 5.30 ± 2.35°, respectively. A positive correlation was observed between angle lambda and spherical equivalent (correlation coefficient = 0.341, p < 0.001). A significant negative correlation was observed between angle lambda and age (correlation coefficient = -0.181, p = 0.036). There was a negative correlation between axial length and angle lambda (correlation coefficient = -0.469, p = 0.003).

The results in this study were in agreement with the results from previous studies. Measuring the distance between the centers of the pupil and the point of corneal reflection using Pentacam is recommended as a quick, objective, quantitative and reproducible method to measure the angle lambda in children.