Videographic Measurement of Binocular alignment with Analysis of the Corneal Limbus

Abstract

Purpose : To present a new videographic method for the quantitative measurement of binocular alignment with analysis of the corneal limbus and to validate the new method by comparing to the prism and alternate cover test (PACT).

Methods : A prospective observational pilot study was performed. We enrolled 15 subjects with esotropia, 40 subjects with exotropia, and 30 orthotropic subjects. The PACT was performed for the measurement of the angle of strabismus by two independent ophthalmologists. Eyes’ videos were obtained with a digital camcorder while an examiner conducted alternate cover test (ACT). The images captured from videos were processed using a Photoshop and analyzed the movement of the corneal limbus for measuring the angle of strabismus. The main outcome measures were Inter-observer variability, test-retest reliability and correlation between the angles of strabismus by both methods.

Results : The 95% limit of agreement of interobserver variability was ±2.8° (4.9 prism diopters) for the PACT and ±2.5° (4.5 prism diopters) for the corneal limbus analysis. The 95% limit of agreement of test-retest reliability between the PACT and corneal limbus analysis was ±5.0° (4.9 prism diopters). Results of the PACT and corneal limbus analysis showed a strong positive correlation (R=0.951, P<0.001).

Conclusions : The new videographic measurement using the analysis of corneal limbus enables precise and objective measurement of binocular alignment. It showed excellent agreement with the PACT and good test-retest reliability, thus proving its reliability and reproducibility.