Abstract
Purpose :
The foveola is the retinal region where cones are most densely packed. Although it covers a miniscule portion of the visual field, this region is disproportionately important in many everyday activities. Yet little is known about how sensitivity varies within the foveola, as the continual presence of eye movements challenges mapping functions at this scale. Movements that are at the resolution limits of standard eye-trackers displace stimuli by large fractions of the foveola. As a consequence, in standard visual field tests, even microperimetry, the entire foveola is represented by a single data point. Here we describe a method to reliably map visual sensitivity across the foveola.
Methods :
We mapped visual sensitivity within the foveola of 6 healthy observers. As in a standard perimetry tests, subjects were asked to detect a small (5’) probe briefly displayed (50 ms) over a uniform background (10 cd/m2). Unlike standard perimetry, however, probes were confined to the central 1 degree of the visual field. Eye movements were tracked at high resolution via digital Dual-Purkinje imaging, a method with sub-arcminute resolution. Probe locations were updated in real-time using a custom device for gaze-contingent display control (delay <5 ms) to compensate for eye movements. A gaze-contingent preliminary calibration enabled localization of the line of sight with arcminute accuracy. By systematically varying the contrast of the probes, we measured contrast sensitivity functions at 13 foveal locations.
Results :
This approach yields high-quality perimetry within the foveola. On average, off-line evaluation of probe positions confirmed that errors in probe presentations were smaller than 1 arcminute. Results were highly repeatable. While individual differences occurred in the overall patterns of sensitivity, peak sensitivity was consistently shifted towards the temporal visual field and favored the horizontal meridian relative to the vertical one. Furthermore, sensitivity progressively deteriorated with increasing eccentricity from the locus of peak sensitivity.
Conclusions :
Recent advances in eye-tracking, gaze-contingent display control, and localization of the line of sight allow reliable high-resolution perimetry of the foveola.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.