Abstract
Purpose :
Standard clinical perimetry uses 0.43 degree stimuli which are influenced by optical blur and retinal eccentricity. We assessed the influence of optical blur on light and dark perimetric stimuli scaled for changes in eccentricity.
Methods :
Three eyes of 3 control subjects were tested using full optical correction followed by 3 levels of optical blur (+1, +3, +5) at the corneal plane with contact lenses. To mitigate the effects of learning, 3 tests preceded the introduction of optical blur. Each test was comprised of 579 trials, including 51 catch trials at 90 different positions in the visual field, each position was repeated 3 times for each the light and dark trials with 6 repeats in each of two blind spot positions.
Hardware consisted of a head mounted display equipped with an eye tracker (HTC VIVE embedded Tobii) with a refresh rate of 90 Hz, a max luminance of 200 cd/m2 and a horizontal field of view of 100 degrees. Unity (version 2017) software was used to generate the stimuli and a library provided by Tobii Pro was used to measure eye movements at 120 Hz. Eye movement was restricted within a central 2.5 degree radius circle. Stimuli were light or dark squares superimposed on a spherical binary noise background. Stimulus size was increased as a function of eccentricity using a power law relationship: stimulus size=minimum scale*(eccentricity/5)α, where the minimum scale is the size in degrees of the stimulus 5 degrees from the fovea, eccentricity is the distance from the fovea in degrees, and alpha is the exponential scale in which the size of the stimulus increases as a function of eccentricity. The minimum scale was set at 2.5 with an alpha of 0.26.
Results :
Response accuracy was recorded as a percentage for each visual field location and intrasubjective comparisons were made between light and dark stimuli as well as between magnitudes of optical blur. Consistent with previous work, subjects were more accurate for darks (~10% error rate) vs. light (~20% error rate) stimuli. There was no change in percentage accuracy with the introduction of optical blur for either lights (p = 0.17) or darks (p = 0.15) (Figure 1).
Conclusions :
Both light and dark perimetric stimuli scaled in size for retinal eccentricity are resistant to blur up to +5 diopters. Scaling perimetric stimuli may be useful in clinical practice.
This is a 2021 ARVO Annual Meeting abstract.