Perimetric Stimuli Undergoing Complete Spatial Summation Optimize the Detection of Retinal Ganglion Cell Density...

To compare the ability of conventional luminance-modulating perimetric stimuli and an area-modulation stimulus (AMS) designed to measure changes in complete spatial summation to identify physiological retinal ganglion cell density (RGCD) gradients in healthy observers.

Contrast thresholds were measured for Goldmann III (GIII; 0.43°, 200 ms) and V (GV; 1.72°, 200 ms) stimuli at 3° and 10° eccentricity in 100 healthy observers (median age, 43 years, range, 18-85 years), with mean spherical equivalent refractive errors ranging from -10.38 to +4.63 DS. Area thresholds were measured at the same locations using a fixed luminance stimulus (ΔL: 4.4 cd/m2, 200 ms). Colocalized RGCD estimates were determined using (i) optical coherence tomography (OCT) RGC layer thickness measures, and (ii) achromatic peripheral grating resolution acuity (PGRA) thresholds. Ratios of the difference in log energy threshold (ΔE) and log RGCD (ΔRGCD) between eccentricities were calculated (ΔE/|ΔRGCD|), with a value of 1 assumed to be the optimal relationship between functional thresholds and RGCD.

ΔE/|ΔRGCD|) values (median and interquartile range [IQR]) were largest for AMS (OCT, 0.54 [IQR, 0.37-0.78]; PGRA, 0.71 [IQR, 0.46-1.19]), followed by GIII (OCT, 0.29 [IQR, 0.08-0.44]; PGRA, 0.33 [IQR, 0.07-0.54]; and GV (OCT, 0.16 [IQR, 0.02-0.29]; and PGRA, 0.19 [IQR, 0.02-0.44]). Interstimulus differences between all stimulus pairs were statistically significant (AMS vs GIII, both P < 0.001; AMS vs GV, both P < 0.001; GIII vs GV, both P < 0.05).

ΔE/|ΔRGCD| values were closest to 1 for AMS, suggesting this stimulus relates best to underlying physiological variations in RGCD.

Thresholds measured with area modulation stimuli vary more proportionally with physiological changes in retinal ganglion cell density relative to conventional perimetric stimuli.