Spatial summation is altered throughout the macula in juvenile X-linked retinoschisis

Abstract

Purpose : Previous studies suggest that the fovea of individuals with juvenile X-linked retinoschisis (XLRS) may be functionally similar to that of the normal periphery. We evaluated this hypothesis by determining the relationship between contrast threshold and stimulus size across the visual field in XLRS subjects.

Methods : Nine subjects with XLRS and 10 age-similar, visually-normal individuals participated. Thresholds were measured at 15 locations along the horizontal meridian of the visual field using a commercially available Octopus visual field perimeter. The field locations were grouped into four regions based on eccentricity from fixation: peripheral (10^o-60^o), perifoveal (5^o-10^o), parafoveal (2^o) and foveal. Stimulus area ranged from 0.01 deg² to 2.32 deg² (Goldmann sizes I to V). Thresholds for the control and XLRS groups were compared statistically by analysis of variance with Bonferroni-corrected pairwise comparisons. The relationship between threshold and stimulus size was described using a spatial summation model to quantify the critical area of spatial summation beyond which threshold is independent of stimulus size.

Results : For measurements in the periphery and perifovea, thresholds were modestly elevated for the XLRS group (less than 2.5x). Threshold differences between groups were significant in the periphery and perifovea for the size I to IV stimuli (p < 0.02), but not for the size V stimulus (p > 0.06). Threshold elevations were larger in the parafovea (4.7x) and fovea (8.4x) for the XLRS group, and pairwise comparisons indicated significant differences for all stimulus sizes (p < 0.001). XLRS thresholds measured in the fovea, parafovea, and perifovea did not differ significantly from those measured from the peripheral field of the control group (p > 0.09). The critical area for spatial summation was significantly larger for all field regions for the XLRS group compared to the control group (p < 0.002).

Conclusions : Spatial summation characteristics of the XLRS fovea, parafovea, and perifovea are similar to those of the normal periphery, suggesting abnormally large receptive field sizes in XLRS. The data indicate that scaling stimulus size can equate thresholds for the XLRS and controls subjects throughout all areas of the visual field.

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