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

Abstract

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] deg2; 5°: 0.32 [0.15-0.65 deg2]) compared to healthy controls (2.5°: 0.08 [0.05-0.13] deg2; 5°: 0.15 [0.08-0.22] deg2) 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.

Figure 1.

Schematic to demonstrate (A) stimuli presented at all test locations examined, and (B) test sequence.

Figure 2.

Boxplots of Ricco's area estimates at 2.5° and 5° visual field eccentricities (pooled across all test locations) for healthy controls (blue) compared to AMD participants (red). The lower and upper limits of the boxes represent the 25th and 75th percentiles of the data, respectively. The error bars extend to the most extreme data point within 1.5× the IQR from the top and bottom of the box. Individual data points for individual observers at each test location are included for reference and color-coded according to disease severity (median area thresholds for the severity groups are represented by horizontal lines).

Figure 3.

Plots of logMAR visual acuity at fixation against Ricco's area estimates at (A) 2.5° and (B) 5° visual field eccentricities in controls (blue) and AMD participants (red).

Figure 4.

Contrast thresholds measured for six stimulus durations with a GIII stimulus (A, B; blue shading) and stimuli scaled to the localized Ricco's area (C, D; purple shading) in healthy controls (blue) and participants with AMD (red). Temporal summation functions fitted to median threshold values are also included in each plot. The dashed line to the x-axis represents the critical duration.

Figure 5.

Critical duration estimates at 2.5° (A) and 5° (B) visual field eccentricities for healthy controls (blue) and participants with AMD (red) with a GIII stimulus and Ricco's area–scaled stimuli. Outliers are represented by “+” markers.

Figure 6.

Mean disease signal (mean log energy threshold difference between AMD and control participants) for all six stimulus durations with the GIII stimulus (blue) compared to Ricco's area (RA)–scaled stimuli (purple) at 2.5° (A) and 5° (B) visual field eccentricities. Outliers are represented by “+” markers. ROC curves indicating the ability of the GIII stimulus (blue) compared to RA-scaled stimuli of 15-frame duration (190.4 ms) to discriminate between AMD and control eyes are presented for 2.5° (C) and 5° (D) visual field eccentricities. Associated AUC values and 95% confidence intervals (shaded regions) are included on each plot (see Methods).