Adaptation mechanisms, eccentricity profiles, and clinical implementation of red-on-white perimetry

Abstract

Aims: To determine the visual adaptation and retinal eccentricity profiles for red flickering and static test stimuli and report a clinical implementation of these stimuli in visual perimetry. Methods: The adaptation profile for red-on-white perimetry stimuli was measured using a threshold-versus-intensity (TvI) paradigm at 0 degrees and 12 degrees eccentricity and by comparing the eccentricity related sensitivity change for red and white, static and flickering targets in young normal trichromats (n=5) and a group of dichromats (n=5). A group of older normal control observers (n=30) were tested and retinal disease was evaluated in persons having age-related maculopathy (ARM: n=35) and diabetes (n=12). Results: Adaptation and eccentricity profiles indicate red static and flickering targets are detected by two mechanisms in the paramacular region, and a single mechanism for >5 degrees eccentricity. The group data for the older normal observers has a high level of inter-observer variability with a generalised reduction in sensitivity across the entire visual field. Group data for the participants with ARM show reduced sensitivities that were pronounced in the central retina. The group data for the diabetic observers return sensitivities that were reduced at all eccentricities. The disease related sensitivity decline was more apparent with red than white stimuli. Conclusions: The adaptation profile and change in sensitivity with retinal eccentricity for the red-on-white perimetric stimuli are consistent with two detection processes. In the macula, the putative detection mechanism is colour-opponent with static targets and non-opponent with flickering targets. At peripheral field locations, the putative detection mechanism is non-opponent for both static and flicker targets. The long wavelength stimuli are less affected the pre-retinal absorption common to ageing. Red-on-white static and flicker perimetry may be useful for monitoring retinal disease, revealing greater abnormalities compared to conventional white-on-white
perimetry, especially in the macula where two detection mechanisms are found.