VOG setup
We used a fixation target (4mm diameter) at 260mm distance (0.881 ° relative to patient view) on a tablet screen (luminosity= 6.17 Lux). The distance to the tablet was constantly maintained by a custom bucket with a chin rest inside and the tablet screen at the bottom of the bucket (Figure 1A). The subject had to hold their heads in the bucket on the chin rest and wore VOG goggles (EyeSeeCamTM, Munich) with a high-speed infrared camera mounted on the goggles frame for right eye positional tracking. We used color-filtered glasses on both eyes (red filter for left eye and blue filter for right eye). For each eye, the color filters allowed only monochromatic view of the target, which changed periodically (2 seconds intervals) from red to blue and vice versa. VOG goggles were branched by USB cable to a laptop and the right eye position was recorded after a calibration procedure using 5 targets on the tablet (center, vertical and horizontal +/- 8.5°). The timing of the target display on the tablet was synchronized with VOG by using WiFi synchronization signals. Synchronization was mandatory for an accurate analysis of skew. The skew values were calculated by detecting the saccades and computing the area under the velocity curve between the start of the first saccade and the end of the last within the event window (-0.5 - 1.5 s around LED switch time).
Subjects were asked to maintain their eyes closed until recording started. We then performed a 10-second long measurement with minimum of 5 trials (target color change) per FP foil.