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° and 5° eccentricities along the 0°, 90°, 180°, and 270° 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°) 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°: 0.21 [0.09–0.41] deg(2); 5°: 0.32 [0.15–0.65 deg(2)]) compared to healthy controls (2.5°: 0.08 [0.05–0.13] deg(2); 5°: 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. TRANSLATIONAL RELEVANCE: The sensitivity of perimetry to AMD may be improved by utilizing stimuli that probe alterations in spatial summation in the disease.