Abstract
Purpose :
The use of mixed reality (MR) displays in education and training have become increasingly commonplace. However, the inherent conflict between vergence and accommodation (VAC) causes concern that these technologies may have an effect on vision. We investigated dynamic accommodation in young adults before and after performing an executive function task in MR.
Methods :
Dynamic accommodation (DA) in diopters (D) was measured (PowerRef 3) in 20 participants (11 males) age 20–24 yrs with habitual correction before and after performing an executive function task (Tower of London) in a head-mounted 3D display (HoloLens 2) for 30 min. The task involved arranging virtual objects at 50 cm distance to match a pattern presented on a physical 2D screen at 4 m. DA was measured over a 1 min period where participants binocularly viewed two accommodative targets, at 40 cm and 4 m, alternately at 3 sec intervals while instructed to keep the targets focused and fused. Data were analyzed using Wilcoxon and Kruskal-Wallis tests and Bonferroni corrections.
Results :
The difference in accommodative change (ΔAC) between near and distance — before and after the MR task — was calculated. Accommodation behavior fell into two groups, those with no difference (<0.012 D, classified as stable) and those with a difference in ΔAC (unstable). Stable and unstable ΔAC median (interquartile range) were +0.10 (0.07) D and +0.26 (0.13) D, respectively, and significantly different from each other (p<0.001). Further analysis showed that those with unstable ΔAC either had contracted ΔAC (smaller ΔAC after the MR task, n=5) or expanded ΔAC (larger ΔAC, n=7). There was a statistically significant difference in ΔAC between the three groups (stable, contracted and expanded) (p=0.002, H=0.70) with pairwise comparisons showing significant differences between all groups (p<0.001). The mean (±SD) ΔAC of the groups were -0.44 (0.26) D, +0.27(0.12) D and 0.27 (0.12) D for the contracted, stable, and expanded groups respectively.
Conclusions :
For some individuals, there was a large difference in accommodation behavior before and after performing the MR task. We hypothesize that the unstable ΔAC could be an effect of the VAC and that using MR over longer time periods could be disadvantageous for individuals with contracted ΔAC. An expanded ΔAC could imply a potential of increased flexibility in the vergence-accommodation system that may be beneficial for these individuals.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.