Assessment of Binocular Alignment Using the 3-Dimensional Strabismus Photo Analyzer

Hee Kyung Yang, MD¹, Sang Beom Han, MD¹, Jeong-Min Hwang, MD¹,
Ho Chul Kang², Chang Bu Jeong², Kwang Gi Kim²

¹Department of Ophthalmology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea
²Biomedical Engineering Branch, Division of Basic & Applied Sciences, National Cancer Center, Goyang, Korea

Purpose: To evaluate the efficacy of the "3D Strabismus Photo Analyzer" on the basis of a 3-dimensional (3D) eye model for estimating binocular alignment of strabismus using photographs.

Design: Observational case series

Participants: One hundred subjects were included as follows: 32 subjects with constant exotropia, 30 subjects with constant esotropia, and 38 subjects who were normal orthotropic controls.

Methods: Two independent ophthalmologists examined the angle of deviation using the modified Krimsky test and prism and alternate cover testing (PCT). Full-face photographs were obtained using an 8.2-megapixel digital single-lens reflex camera, and the images were analyzed using the 3D Strabismus Photo Analyzer to estimate the angle of deviation between both eyes. The images were adjusted for age-dependent ophthalmic biometry and angle kappa.
Main outcome Measures: Interobserver test-retest reliability, intertest test-retest reliability, and correlation between the angle of deviation measured by the modified Krimsky test, PCT, and 3D Strabismus Photo Analyzer.

Results: Regarding interobserver test-retest reliability, the half-width of the 95% limit of agreement was 3.5° for the modified Krimsky test, 3.1° for the PCT, and 1.5° for the 3D Strabismus Photo Analyzer. The half-width of the 95% limit of agreement for the intertest test-retest reliability between each pair of methods was 2.8° for the 3D Strabismus Photo Analyzer versus modified Krimsky test, 5.5° for the modified Krimsky test versus PCT, and 5.8° for the 3D Strabismus Photo Analyzer versus PCT. Results of the modified Krimsky test and 3D Strabismus Photo Analyzer showed a strong positive correlation (R = .990, P < .001), and there was no significant difference according to the type of deviation (exotropia: R = .957, P < .001; esotropia: R = .949, P < .001).

Conclusions: The 3D Strabismus Photo Analyzer is a simple and reliable tool for measuring the angle of strabismus in patients in whom PCT cannot be performed. It shows excellent agreement with the modified Krimsky test and substantially improved reproducibility compared to manual methods.