Increment/Decrement Perimetry in Glaucomatous Observers in a Virtual Reality Environment

Abstract

Purpose : Clinical perimetry is limited to the assessment of contrast sensitivity of the ON cortical pathway. Our goal is to test the feasibility and applicability of a clinical assessment of both the ON and OFF pathways in patients with glaucoma and controls.

Methods : Subjects included 12 patients with early to moderate primary open angle glaucoma (mean=69.75 years, std=7.64), and 12 controls (mean=63.67 years, std=4.25). We used a head mounted display equipped with an eye tracker (HTC VIVE embedded Tobii). Commercially available, free software (Unity, version 2017) was used to create the stimuli and a library provided by Tobii Pro was used to measure eye movements at 120 Hz.

Increment and decrement stimuli were presented as black and white squares on a binary noise background. Stimuli size changed as a function of eccentricity using a power law relationship: stimulus size= minimum scale*(eccentricity/5)^α. Eye movement was restricted to a central circle with a 2.5 degree radius. Observers were given hand held response buttons in each hand and were instructed to respond with the response button that corresponded with the side of the visual field on which the stimulus was presented. If the observer did not see a stimulus they were instructed to not respond and wait for the next stimulus to appear. A total of 528 trials, including 24 catch trials, were tested in 84 locations with 3 repeats for both increment and decrement stimuli.

Results : The relationship between the percentage of correct responses for increment and decrement stimuli follows a power function, wherein glaucoma and controls overlap (R² = 0.842) (Figure 1a). This overlap decreases when we quantify only the subthreshold (unseen) increment targets in a linear relationship (R² = 0.7074) (Figure 1b). All controls had less than 12% of subthreshold increment targets, whereas the percentage of subthreshold targets was higher for 75% of the glaucoma subjects, even in early stages of the disease (-1.72 dB of visual sensitivity loss). Increment/decrement perimetry measured large increment visual deficits in patients with limited loss of visual sensitivity (Figure 1c), which may improve detection of early disease.

Conclusions : Increment/decrement perimetry is feasible in a VR environment. Future work will focus on optimizing stimulus parameters to improve the sensitivity and specificity of this test.

This is a 2020 ARVO Annual Meeting abstract.