Changes in tonic accommodation and vergence after immersion in a virtual-reality environment

The aim of this experiment was to establish the effect of virtual-reality (VR) stimulation upon the tonic elements of the accommodation and vergence controllers. Twenty emmetropic subjects (mean age 22.0 ± 4.5 years) participated in the experiment. Tonic accommodation (TA) was measured in darkness with the Shin-Nippon SRW-5000 infrared autorefractor. Tonic vergence (TV) was measured with an Eyetrace 300× infrared limbal eye-tracker. Subjects were then immersed in a VR environment for 30 min, generated with SimulEyes field-sequential shutter goggles controlled by a Dell XPS R450 PC. Following immersion, measurements of TA and TV were repeated. Mean pre-task TV was 1.89 ± 3.30 metre angles (MA). The TV became significantly (p < 0.005) more divergent as a result of the VR stimulation (mean change 3.58 ± 5.26 MA). Pre-task TA (0.41 ± 0.73 D) was not significantly different from post-task TA (0.34 ± 0.70 D). We found that the VR environment produced substantial adaptation of TV in the divergent direction. There are no significant changes in TA in the VR environment. These findings suggest that the initial reaction of the accommodation and vergence controllers is to shift vergence bias in order to minimise the stimulus conflicts found in VR environments. This enables subjects to maintain a stable accommodation response despite continual changes in the vergence position.