RESUMEN
The human visual system evolved in environments with statistical regularities. Binocular vision is adapted to these such that depth perception and eye movements are more precise, faster, and performed comfortably in environments consistent with the regularities. We measured the statistics of eye movements and binocular disparities in virtual-reality (VR) - gaming environments and found that they are quite different from those in the natural environment. Fixation distance and direction are more restricted in VR, and fixation distance is farther. The pattern of disparity across the visual field is less regular in VR and does not conform to a prominent property of naturally occurring disparities. From this we predict that double vision is more likely in VR than in the natural environment. We also determined the optimal screen distance to minimize discomfort due to the vergence-accommodation conflict, and the optimal nasal-temporal positioning of head-mounted display (HMD) screens to maximize binocular field of view. Finally, in a user study we investigated how VR content affects comfort and performance. Content that is more consistent with the statistics of the natural world yields less discomfort than content that is not. Furthermore, consistent content yields slightly better performance than inconsistent content.
RESUMEN
PURPOSE: The ±2.00 D accommodative facility test presents several limitations, including the lack of objective information and inherent characteristics such as vergence/accommodative conflict, change in apparent size of the image, subjective criteria for judging blur and motor reaction time. By using free-space viewing conditions and an open-field autorefractor to monitor the refractive state, we examined the impact of manipulating these factors on the qualitative and quantitative assessment of accommodative facility. METHODS: Twenty-five healthy young adults (24.5 ± 4.5 years) took part in this study. Participants performed three accommodative facility tests (adapted flipper, 4D free-space viewing and 2.5D free-space viewing) under both monocular and binocular conditions in random order. A binocular open-field autorefractor was used to assess the accommodative response continuously, and these data were used to characterise accommodative facility quantitatively and qualitatively. RESULTS: There were statistically significant differences between the three testing methods both quantitatively (p < 0.001) and qualitatively (p = 0.02). For the same accommodative demand, a lower number of cycles was obtained for the adapted flipper condition in comparison with the 4D free-space viewing test (corrected p-value < 0.001, Cohen's d = 0.78). However, this comparison did not reach statistical significance for qualitative measures of accommodative facility (corrected p-value = 0.82, Cohen's d 0.05). CONCLUSIONS: These data provide evidence that the qualitative assessment of accommodative facility is not influenced by the inherent limitations of the ±2.00 D flipper test. The use of qualitative outcomes by incorporating an open-field autorefractor allows examiners to increase the validity of the accommodative facility test in both clinical and research settings.