Two-color full-field stimulus thresholds under scotopic and photopic conditions in inherited retinal degenerations

Abstract

Purpose : The full-field stimulus test (FST), a measure of visual sensitivity typically obtained under dark-adapted conditions, is correlated with the most sensitive location of the visual field measured by dark-adapted static perimetry. The purpose of this study was to perform a comprehensive analysis of the FST under dark-adapted (DA) and light-adapted (LA) conditions with red and blue light, and to determine their relationship with visual field area assessed by kinetic perimetry.

Methods : Eleven subjects with a known diagnosis of an inherited retinal degeneration (IRD) participated. Visual field area was determined using an Octopus 900 kinetic perimeter with three target sizes (V4e, III4e, and I4e). Area of scotomata, if present, were subtracted from the recorded field area. FST thresholds were obtained with photopically matched (cd/m²) red (632 nm) and blue (468 nm) stimuli under LA and DA conditions. DA-FST (red and blue) thresholds were compared with LA-FST (red and blue) thresholds. DA-FST (red and blue) and LA-FST (red and blue) thresholds were also compared with the visual field areas.

Results : FST thresholds for red and blue stimuli were highly correlated under DA (r = 0.94, p < 0.001) and LA (r = 0.95, p < 0.001) conditions. For 9 of the 11 subjects, DA-FST threshold was approximately 2.2 log units higher for the red stimulus than for the blue stimulus. The remaining 2 subjects had equal red and blue DA-FST thresholds, consistent with their clinically apparent lack of rod function. LA-FST threshold was approximately 0.2 log units higher for the red stimulus than for the blue stimulus. For subjects with nearly normal visual fields (where log₁₀ (visual field area [degrees²]) > 3.5), FST values varied widely, with no measurable dependence on visual field area. In contrast, for subjects with reduced visual field areas, FST thresholds increased as visual field area decreased.

Conclusions : FST threshold differences between red and blue stimuli were consistent with predictions based on the scotopic and photopic spectral sensitivity functions, allowing the quantification of full-field rod- and cone-pathway sensitivity in this cohort of IRD patients. For subjects with marked field loss, FST thresholds were associated with kinetic field area.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.