Participants were seated 60 cm in front of a 30-inch computer screen (Dell U3011, 2560 × 1600 pixels) in an otherwise dark, soundproof room. The position of both eyes was measured with a remote eye-tracking system (Eyelink 1000 Plus, SR Research) at a sampling rate of 500 Hz per eye. Subjects were asked to keep their head still during the measurements with the help of a chin rest. A target sticker on the forehead ensured steady tracking even when small head movements occurred. The stimulus software was written in Matlab (version 2014) using the Psychophysics Toolbox extension30 (link) and executed on a laptop computer equipped with an open GL graphics card.
A 13-point calibration of the eye tracker was carried out prior to each measurement. The calibration targets were filled white circles with a diameter of 1 degree against a black background. We ensured that each eye was calibrated individually while the other eye was covered. This monocular viewing forced the participants to use the PRL of that eye during fixation of the calibration targets. NV controls and patients with RP all had foveal PRLs. All but one patient with AMD had peripheral PRLs, located using the MAIA microperimetry records. The most eccentric calibration points were sometimes not visible to the subjects with RP because of their limited peripheral vision. In these cases, the experimenter verbally directed the subject to the location of the calibration target or audibly tapped on the screen to help them find it.
A 13-point calibration of the eye tracker was carried out prior to each measurement. The calibration targets were filled white circles with a diameter of 1 degree against a black background. We ensured that each eye was calibrated individually while the other eye was covered. This monocular viewing forced the participants to use the PRL of that eye during fixation of the calibration targets. NV controls and patients with RP all had foveal PRLs. All but one patient with AMD had peripheral PRLs, located using the MAIA microperimetry records. The most eccentric calibration points were sometimes not visible to the subjects with RP because of their limited peripheral vision. In these cases, the experimenter verbally directed the subject to the location of the calibration target or audibly tapped on the screen to help them find it.
