Abstract
Purpose :
Perimetry is an important clinical and research tool. It can be used to track the neural pathology of disease or to understand their processes. Determining response characteristics to stimuli that target specific visual pathways may offer information on how to better assess their function and improve current perimetry technologies. A previous study revealed the linearity of chromatic parvocellular summation and its potential for improved perimetry test consistency. The purpose of this study is to characterize the spatial summation of chromatic koniocellular stimuli.
Methods :
Chromatic contrast detection thresholds to circular patches were measured as a function of size and eccentricity in four subjects. Stimuli modulated towards either meridian of the +S-(L+M) axis of Derrington, Krauskopf, and Lennie color space. The average luminance of the display was 10 cd/m2, with luminance noise introduced to prevent potential cues. Stimuli ranging in size from 0.25° to 4.0° in diameter were tested at 5° intervals up to 20° retinal eccentricity. Four oblique locations were tested at each eccentricity using interleaved staircases. Subjects indicated the perceived location of the stimulus by button press. Contrasts were calculated as LMS cone contrasts and fit with four models: a linear model, a decay model, a hinged bilinear model with the initial slope constrained to -1, and a hinged bilinear model without constraints.
Results :
For most koniocellular conditions, Bayesian model comparison revealed preference for the decay or unconstrained hinged models, however, effects were not significant in all cases. Using parameter estimates from the constrained hinged model revealed an average slope of -0.4 across all conditions for partial summation. In the +S direction, conditions that gave reliable estimates revealed average critical areas of 0.09, 0.11, and 0.28 degree2 within 15° eccentricity. In the –(L+M) direction, average critical areas of 0.13, 0.27, and 0.42 were found within the same eccentricity range.
Conclusions :
Similar to achromatic spatial summation, koniocellular functions showed some degree of non-linearity, unlike the linear functions previously reported for parvocellular stimuli. Critical areas between the koniocellular and achromatic conditions were comparable as well. These similarities likely indicate contributions from a non-retinal locus.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.