A Digital Alternative to the TNO Stereo Test to Qualify Military Aircrew

INTRODUCTION: Stereopsis is usually required in military aviators and may become increasingly important with reliance on newer technologies such as binocular Helmet-Mounted Displays (HMDs) and stereo displays. The current stereo test used to qualify UK military aircrew (TNO test) has many limitations. To address these limitations, two computer-based digital versions of a random dot stereogram (RDS) were developed: a static version (dRDS-S), and a version in which the dots appear to move dynamically within the depth plane (dRDS-D), both capable of measuring stereo acuity to threshold.METHODS: There were 41 participants who performed all 3 stereo tests, TNO and both digital dRDS tests, on two separate occasions.RESULTS: The best (lowest) mean stereo acuity threshold was measured with dRDS-S (33.79 arcseconds, range 12.64-173) and the worst mean stereo acuity thresholds were measured with the TNO test (91 arcseconds, range 60-240). Both dRDS tests were strongly correlated, but neither correlated with the TNO test. Both dRDS tests were more reliable, as indicated with tighter limits of agreement.DISCUSSION: With a large floor effect at 60 arcseconds, the TNO test was unable to characterize any finer degree of stereo acuity. Both dRDS tests demonstrated better test-retest reliability and addressed many of the limitations seen with the TNO test. The dRDS tests were not correlated with the TNO test, which suggests that the TNO test does not provide the accuracy or reliability for use as a meaningful aeromedical screening test. The dRDS tests will enable research to investigate the relationship between stereo acuity and operational performance.Posselt BN, Seemiller E, Winterbottom M, Baber C, Hadley S.