# Perceived Brightness and Resolution of Holographic Augmented Reality Retinal Scan Glasses
## 2 Materials and Methods
### Perceived Resolution Study Design  
To measure the perceived resolution of the BML500P RS glasses prototype, we conducted a psychophysical discrimination test with 20 participants (17 males, 3 females; aged 18-60 years, mean \(\pm\) sd: 36.0 \(\pm\) 7.7 years). We implemented a prescreening routine for visual acuity and contrast sensitivity with Landolt rings and a test for color vision with color plates to ensure a minimum standard level of vision ability among all participants. Participants who could not pass these screening tests were not included in the study. Inclusion criteria were right-eye dominancy, a right monocular visual acuity of at least 0.8 decimal (screening results: logMAR mean \(\pm\) sd: \(-\)0.073 \(\pm\) 0.060), a right monocular contrast vision threshold below 15% Weber contrast (mean \(\pm\) sd: 4.2 \(\pm\) 0.8%), no color vision deficiency, and no known eye diseases. The experiment was approved by the ethics committee of the Medical Faculty of the University of Tubingen (Code 410/2022B02) and conducted according to the provisions of the Declaration of Helsinki. Informed consent was obtained from all participants. The study setup is shown in Figure 4. Participants were equipped with the RS glasses on a chinrest 2.3 m in front of a 60-inch LED monitor (PN-R603; Sharp Corporation; Sakai, Osaka, Japan). The light-isolated examination room was illuminated at an average of 2500 lux, equal to outdoor illumination on a cloudy day. Participants were shown a right-eye monocular stimulus in the glasses with a size of 11.15 \(\pm\) 0.22 deg \(\times\) 14.99 \(\pm\) 0.17 deg [mean \(\pm\) sd from 10 measurements]. The transparent RS glasses superimposed this virtual image onto the real image from the LED monitor. Psychopy [9] was used to control the monitor and RS glasses stimuli simultaneously. To minimize distractions, participants wore a black eye patch over their left eye. The glasses stimulus was picked randomly from a selection of monochromatic line patterns with different spatial frequencies from 1.8 cyc/deg to 16.0 cyc/deg and a full monochromatic rectangle. The line pattern consisted of lines with equal digital pixel width for both projection and non-illuminated dark background lines. The spatial frequency  
Figure 3: Beam paths of a single pixel entering the eye for a Lambertian display (**top**) and an RS display (**bottom**). An ideal cornea and lens (**left**) focus light from a single pixel onto a narrow point on the retina. Aberrations of the cornea and lens (**middle**) or an out-of-focus retinal plane in myopia or hyperopia (**right**) have a much smaller impact on the focus and perceived resolution of an RS image. range of the lines was determined by the 480 \(\times\) 320 pixels that could be set within the software configuration of the prototype. The pattern with the highest spatial frequency had a width of one digital pixel. For high digital spatial frequencies, the resulting optical lines started to blur into a full rectangle. The task of the participants was to report whether they saw lines or a rectangle using a wireless keyboard. The spatial frequency of the lines was adjusted based on the participants' responses using a 3-down 1-up staircase algorithm to determine the highest resolvable spatial frequency. The algorithm terminated after three reversals. There was no time limit for responses. To ensure that a staircase level could not be passed by only identifying rectangles, a line pattern was always presented after two correct responses. A 0.5 s pause between stimuli was added to avoid afterimages and to reduce cues from stimulus transitions.