A comparison of stereopsis with ANVIS and F4949 night vision goggles.

BACKGROUND: This study was undertaken to see if the model of NVG affects stereoacuity. METHODS: We tested 13 male and 2 female aircrew with the Aviator's Night Vision Imaging System (ANVIS) and F4949 NVGs. Visual acuity was measured using the NVG Resolution Grid and stereopsis was determined using a modified Howard-Dolman test. RESULTS: In simulated light conditions, average stereoscopic threshold using the F4949 NVG (17.35 arc s) was not significantly better than the ANVIS NVG (18.42 arc s), the mean difference being 1.07 arc s (95% confidence limits, -2.85 to 4.99). CONCLUSIONS: The Howard-Dolman test proved to be effective in eliminating monocular clues, thus validating its use in testing NVG stereopsis. The distribution of visual acuities across subjects and goggle models was too narrow to evaluate the effect of visual acuity on stereoacuity in NVGs. Differences in trial means during the course of the study indicated the presence of a "learning" effect on the Howard-Dolman test.