Abstract
Purpose :
Stimuli with pattern (image) blur are robust to optical defocus during visual field (VF) testing. We sought to extend this finding to virtual reality (VR) using a head-mounted display, and to find the stimulus size below which this robustness to defocus failed.
Methods :
Stimuli were displayed bi-ocularly on a Facebook Oculus Rift (TM) operating at 90 Hz, driven by a Windows computer using Vivid Vision Perimetry (TM), version 2.725 (Vivid Vision Inc, San Francisco CA) software. Stimulus luminance profiles consisted of 3 equal size zones: a flat (dark) center flanked by sunken cosines. Diameters ranged from 0.19-1.4 deg width at 1/2 height. 12 evenly spaced stimuli were presented one eccentricity at a time, at 2, 4, 7.5, 12, 20, and 30 deg. Background luminance was 48.1 cd/m2 and stimuli had Weber contrast of 34.5% or 99%. Subjects, aged 21-26, were free of ocular disease and wore contact lenses (CLs) for 20/20 acuity or better. HVFA 24-2 SITA Standard test were used to verify that baseline VFs were normal. VR testing was repeated with CLs that increased myopic blur by 2, 4, 5 and 6D.
Results :
114 visual fields of 19 subjects were analyzed. Each field was given a Mean Seen Score (MSS) between 0 (no high-contrast stimuli seen) and 10 (low-contrast stimuli seen at all locations). 3-way ANOVA with fixed factors Size (6 levels) and Blur (4 levels), and random factor Subject, showed significant effects for Blur (p < .0001) and Size (0.0001), as well as interactions Subject x Size (.001) and Blur x Size (.0001). Paired comparisons (one-tailed paired t-tests with Bonferroni correction) showed significant effects of defocus for the smallest stimuli when defocus was 4D (.0001) or 5-6D (.0001), and for the next smallest stimuli when defocus was 5-6D (.0004), but not for any other defocused stimuli. A clinically significant change in MSS was taken to be 0.2 or greater. For stimuli of 0.43 deg (Goldmann Size III) or larger, defocus up to 5D had no clinically or statistically significant effect.
Conclusions :
Decrement perimetric stimuli with pattern blur in a VR perimetric screening test were resistant to optical blur up to 5 diopters for stimuli of Goldmann size III or larger. Future work will focus on further stimulus refinement and determining the sensitivity and specificity of the test in the setting of glaucoma and visual track disorders
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.