Abstract
Purpose :
Strabismus is a developmental visual impairment affecting 3-5% of children that can cause impaired binocular vision and a broad range of educational and social disadvantages. Strabismus assessment and treatment prioritizes near-distance primary gaze. To quantify strabismus at multiple gaze directions and depths, we developed a novel multi-depth plane display consisting of three screens at 0.4m, 1.26m and 4m.
Methods :
Ocular deviation was measured in seven adults who reported a strabismus diagnosis during childhood and two typically sighted controls. Subjects were shown 27 targets in random order in a 3x3x3 grid with 10° between adjacent targets. While participants fixated on each target, an automated cover test was performed by occluding OS or OD with a LCD shutter for 2.25 sec. A head mounted eye-tracker recorded eye movements at 200Hz, and ocular deviation was calculated from the change in eye pupil position between OS, OD, and OU viewing. An optometrist also conducted a standard prism cover test (PCT) at 1m and 4m.
Results :
For the controls, the overall mean deviation ± standard deviation was 0.91° ± 1.3° across gaze direction and depth, and the PCT detected no tropia. Five strabismics had received vision and/or amblyopia therapy and two had undergone surgery. Three of these subjects manifested deviations in the PCT that were correlated with eye tracker deviations at primary gaze. The overall mean ocular deviation of strabismic eyes (the eye with the larger deviation) across all directions and depths ranged from 0.32° ± 0.22° to 7.6° ± 2.3° in vision therapy subjects, and 1.2° ± 1.7° to 3.4° ± 2.1° in surgery subjects. The effect of depth and gaze direction on ocular deviation was highly idiosyncratic, e.g., for one vision therapy subject, deviations ranged from 15.8° ± 1.3° for the bottom right target at 4m to 1.9° ± 0.18° for the top target at 0.4m. In contrast, deviation was <0.4° in all directions and depths in another vision therapy subject.
Conclusions :
Ocular deviations are highly dependent on gaze direction and depth in observers with a history of strabismus. Strabismus may manifest away from primary gaze and depth and may differentially impact binocular visual function. Comprehensive assessment of strabismus therefore requires measurement across multiple directions and depths of gaze and may be performed with an automated system.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.