A Novel Device for Quick Quantification of Binocular Misalignment without Recording Eye Movements

Background: Otolith pathology may cause vertical or torsional ocular misalignment, known to differ when positioned supine versus upright. We have developed a handheld, portable technology that uses a perceptual measure to quantify ocular misalignment.

Objective: Vertical Alignment Nulling (VAN) and Torsional Alignment Nulling (TAN) tests were assessed for stability across time, for differences in upright versus supine position and for differences across healthy control, patients with vestibular hypofunction (UVH), and veterans with multisensory impairment (MSI).

Method: To date, 20 patients, 9 veterans and 20 healthy control subjects enrolled the study. Subjects view one red and one blue line on a tablet computer while looking through color-matched red and blue filters. Subjects align the red and blue lines, initially vertically offset from one another during VAN or rotated relative to one another during TAN, until they perceive a single continuous line. Ocular misalignments are inferred from residual offsets in the final line position. During testing, all binocular visual cues that would otherwise confound the misalignment results are eliminated by utilizing OLED technology and testing in a completely darkened room.

Results: Both VAN and TAN are very stable within the same day and between days with no significant differences. Variability of performances (coefficient of variant (CV) of mean magnitude of misalignment) revealed differences between patients groups and healthy controls in addition to a significant change in groups’ misalignment CV between testing positions. Measurement is sensitive for detecting small misalignment; however, mean magnitude of misalignment is not a sensitive score to distinguish between groups.

Conclusion: VAN and TAN ocular misalignment tests are stable and valid. Variability of misalignment between groups and, the amount of change in variability between testing positions (upright versus supine) seems to be the best indicator for the ocular misalignment cause (UVH, MSI, muscular).