Abstract
Purpose :
The use of augmented and virtual reality displays often cause visual fatigue and eye strain and may hinder performance, especially when viewing near content due to crossed-vergence-accommodation conflict (VAC, virtual content nearer than the display’s focal depth). The aim was to objectively assess the change of vergence and accommodation during induced VAC at near.
Methods :
Refraction and gaze responses were measured with a photorefractor (Poweref3) during positive fusional vergence (base out prisms) in 14 young adults (20–24 yr, 6 males) wearing their habitual correction. The target was presented at 2 m and consisted of a vertical row of letters each subtending 0.4 logMAR. Prisms were increased in steps for 5 s per step, and participants were instructed to keep the target focused and fused, and to report the points of blur, break (diplopia), and recovery of fusion. Vergence (in meter angle, MA, computed from gaze) and accommodation responses (in diopters, D, computed from refraction) were calculated for six measurements; pre-prism (PP), the two prism measures immediately prior to blur (PB1, PB2), blur (B), break (BR) and recovery (R). Comparisons across measurements were made for vergence and accommodation separately using the Kruskal-Wallis test, and pairwise Wilcoxon test with Bonferroni corrections for comparisons between measures.
Results :
The median(IQR) for the vergence measures were: PP 0.30(0.48), PB1 0.33(0.41), PB2 0.52(0.37), B 0.32(0.34), BR -1.04(1.72), R 0.31(0.90) MA. There was a statistically significant difference between the vergence response measures (H(5)=14.6, p=0.012) in which only BP2 and BR were significantly different from each other (Z=167, p=0.027). The median(IQR) for the accommodation measures were: PP -0.56(0.81), PB1 -0.50(1.19), PB2 -0.54(1.38), B -0.31(1.35), BR -0.76(1.67), R -0.41(1.94) D. There was no statistically significant difference between the accommodation response measures (H(5)=1.1, p=0.953).
Conclusions :
While the vergence responses dropped at break, the measured accommodation responses did not change over time. This suggests that vergence, not accommodation, drives the experience of subjective blur in crossed-VAC at near. There were individual differences requiring further research to understand their role in relation to visual fatigue and eye strain.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.