Virtual reality-based Harms tangent screen test for strabismus measurement

Our study presents a virtual reality-based tangent screen test (VTS) to measure subjective ocular deviations including torsion in nine directions of gaze. The test was compared to the analogous Harms tangent screen test (HTS).

We used an Oculus Go^® controller and head-mounted-display with rotation sensors to measure patient's head orientation for the VTS. The software was developed with Unity^®. We assessed subjective squint angles of adult patients with eye motility disorders of different origin in nine positions of gaze by means of HTS and VTS. We calculated mean difference, 95% limits of agreement and intraclass correlations (ICC) for horizontal, vertical and torsional deviations.

We included 85 patients. Measured horizontal and vertical deviations showed very good agreement between the two methods in all gaze directions (horizontal and vertical ICC: 0.93-0.98). Agreement was lower for torsional deviations (ICC: 0.79-0.93). The mean difference in primary position was 1.5° (95% limits of agreement -3.5° to 6.5°) for horizontal, 0° (-2,7° to 2,7°) for vertical, and 0.3° (-4.0° to 3.0°) for torsional deviations. The average examination time was 6 min with the VTS compared to 15 min with the HTS.

Vertical and horizontal deviations showed good agreement between both tests measuring a slightly higher esodeviation with VTS probably due to an increased vergence demand. Measurement of torsional misalignment would benefit from a controller with more holding stability, such as a PC-mouse with central wheel, facilitating fine adjustments. VTS allowed automatic documentation, required less time and was easier to use than HTS.

What is known The incidence of neurogenic diplopia increases in the ageing population. The Harms tangent screen test (HTS) reliably measures subjective ocular deviations in patients with diplopia. The HTS requires staff well-trained in orthoptics limiting its use. What is new A novel virtual reality-based tangent screen test (VTS) enables measurement of horizontal, vertical and torsional ocular misalignment and shows a good comparability to the HTS. VTS uses commercially available head-mounted-display and controller, and specifically developed software, requires less time than HTS and allows automatic documentation. VTS administration does not require orthoptic training and can eventually be implemented in a clinical setting to provide a wider availability of subjective squint angle measurements.