Investigating the Spatiotemporal Summation of Perimetric Stimuli in Dry Age-Related Macular Degeneration

Purpose: To measure achromatic spatial, temporal, and spatiotemporal summation in dry age-related macular degeneration (AMD) compared to healthy controls under conditions of photopic gaze-contingent perimetry.Methods: Twenty participants with dry AMD (mean age, 74.6 years) and 20 healthy controls (mean age, 67.8 years) performed custom, gaze-contingent perimetry tests. An area-modulation test generated localized estimates of Ricco's area (RA) at 2.5 degrees and 5 degrees eccentricities along the 0 degrees, 90 degrees, 180 degrees, and 270 degrees meridians. Contrast thresholds were measured at the same test locations for stimuli of six durations (3.7-190.4 ms) with a Goldmann III stimulus (GIII, 0.43 degrees) and RA-scaled stimuli. The upper limit (critical duration) of complete temporal summation (using the GIII stimulus) and spatiotemporal summation (using the RA stimuli) was estimated using iterative two-phase regression analysis.Results: Median (interquartile range [IQR]) RA estimates were significantly larger in AMD participants (2.5 degrees: 0.21 [0.09-0.41] deg(2); 5 degrees: 0.32 [0.15-0.65 deg(2)]) compared to healthy controls (2.5 degrees: 0.08 [0.05-0.13] deg(2); 5 degrees: 0.15 [0.08-0.22] deg(2)) at all test locations (all P < 0.05). No significant difference in median critical duration was found in AMD participants with the GIII stimulus (19.6 [9.9-30.4] ms) and RA-scaled stimuli (22.9 [13.9-40.3] ms) compared to healthy controls (GIII: 17.0 [11.3-24.0] ms; RA-scaled: 22.4 [14.3-33.1] ms) at all test locations (all P > 0.05).Conclusions: Spatial summation is altered in dry AMD, without commensurate changes in temporal summation.