Figure 1. Cone-resolved adaptive optics micro-psychophysics.

(a) Schematic of cell-resolved visual acuity testing in the human foveola with an adaptive optics scanning laser ophthalmoscope (AOSLO). Stimuli were dark Snellen-E optotypes presented at variable sizes and four orientations in the center of the 788 nm AOSLO imaging raster. Participants responded by indicating stimulus orientation during natural viewing, i.e., unrestricted eye motion. (b) Exemplary single trial retinal motion trace and strip-wise image stabilization of a single AOSLO frame (shown here during a microsaccade for better visibility). Trials containing microsaccades or blinks during the 500 ms stimulus presentation (gray shaded area) were excluded. The x-axis grid represents individual video frames (33 ms). (c) Foveolar retinal cone mosaic with a exemplary single trial retinal motion across the stimulus. Time is represented by color from stimulus onset to offset (purple to yellow). The cone density centroid (CDC) is shown as a red circle with white fill. (d) Typical psychophysical data of five consecutive runs in one eye. Each run followed a QUEST procedure with 20 trials. (e) Psychometric function fit to the data (about 100 trials). Acuity thresholds were estimated at 62.5% correct responses. (f) Exemplary retinal images (upper rows) and corresponding cone activation patterns (lower rows) of one experimental run (20 trials from top left to bottom right). Cone activation patterns are shown for a representative single frame. See Videos 1 and 2 for a real-time video representation.