Automated analysis of binocular alignment using an infrared camera and selective wavelength filter

We present a computerized method of measuring binocular alignment using a selective wavelength filter and an infrared camera, and validate the efficacy of automated image analysis compared to the gold standard prism and alternate cover test (PCT).

A prospective observational pilot study was performed on 30 subjects with intermittent exotropia, 30 subjects with esotropia, and 30 orthotropic subjects who were able to cooperate with the PCT. Two independent ophthalmologists examined the angle of deviation using the PCT. Full-face images were obtained with an infrared camera while a selective wavelength filter was placed in front of either eye. Images were analyzed using the 3D Strabismus Photo Analyzer. Interobserver variability, test-retest reliability and correlation between the angles of deviation were determined for both methods.

The 95% limit of agreement of interobserver variability was ± 4.8 prism diopters (PD) for the PCT and ± 4.3 PD for the selective wavelength filter analysis. The 95% limit of agreement of test-retest reliability between the PCT and selective wavelength filter analysis was ± 8.5 PD. Results of the PCT and selective wavelength filter analysis showed a strong positive correlation (R = 0.900, P < 0.001).

Infrared images acquired with a selective wavelength filter can detect the latent components of strabismus, and automated image analysis showed excellent agreement with the standard PCT. This automated method is an accurate and reliable tool for measuring ocular deviation with minimal observer dependency.