Frequency-of-seeing curves (psychometric functions) for perimetric stimuli in age-related macular degeneration

Abstract

Purpose: Frequency-of-seeing (FoS) curves (psychometric functions) for perimetric stimuli have been widely used in computer simulations of new visual field test procedures. FoS curves for age-related macular degeneration (AMD) are not available in the literature and are needed for the development of improved microperimetry test procedures, which are of particular interest for use as clinical trial endpoints.

Methods: Data were refitted from a previous study to generate FoS curves for 20 participants with AMD, each tested at nine locations within the central 10°. Stimulus parameters, background luminance and dB scale were matched to the MAIA-2 microperimeter, and stimuli were presented in a method of constant stimuli to build up FoS curves over multiple runs. FoS curves were fitted with a modified cumulative Gaussian function. The relationship between sensitivity and slope of fitted FoS curves was modelled by robust linear regression, producing models both with and without an eccentricity parameter.

Results: FoS curves were satisfactorily fitted to data from 174 visual field locations in 20 participants (age 65-83 years, 11 female). Each curve was made up of a median of 243 (range 177-297) stimulus presentations over a median of 12 (range 9-32) levels. Median sensitivity was 25.5 dB (range 3.8-31.4 dB). The median slope (SD of fitted function) was 1.6 dB (range 0.5-8.5 dB). As in previous studies of other conditions, the slope of fitted FoS curves increased as sensitivity decreased (p < 0.001).

Conclusions: FoS are provided for participants with AMD, as well as models of the relationship between sensitivity and slope. These fitted models and data may be useful for computer simulation studies of microperimetry procedures. Full details of the fitted curves are provided as supporting information.

Keywords: age‐related macular degeneration; frequency‐of‐seeing; microperimetry; perimetry; psychometric function.

FIGURE 1

Example frequency‐of‐seeing (FoS) curves from the participant with the highest median sensitivity (participant 7, upper panel) and the participant with the lowest median sensitivity (participant 4, lower panel). Red, green and blue curves/points represent the lowest, median and highest sensitivity locations, respectively. Points show the percentage correct for stimuli at each contrast (intensity) level, with the number of presentations at each level given by the overlaid numbers on each point. Curves show the fitted FoS curves. These curves are plotted separately along with details of fitted parameters in Appendices S1 and S2.

FIGURE 2

Sensitivity versus slope for the fitted frequency‐of‐seeing (FoS) curves. The solid black line shows the fit of Equation 2 to the data (95% confidence interval shown by black dashed lines). The blue‐shaded area shows the 95% prediction interval of the fit.