Abstract
Purpose :
One of the possible applications of two-photon vision is its implementation in retinal displays. This study aims to investigate the effect of defocusing on contrast sensitivity for two-photon vision, enabling a better assessment of the potential application of the phenomenon in Augmented Reality (AR) technology.
Methods :
The study included 5 healthy volunteers (3W, 2M, aged 25 – 46) with no diagnosed visual system pathologies. Contrast sensitivity functions (CSFs) were assessed for four spatial frequencies within the range of 1 – 24 cycles per degree (cpd) using the tumbling E optotype in a four-alternative forced-choice procedure. The optotype was projected onto the retina through scanning with pulsed 520 nm or 1040 nm laser beams (200 fs, 76 MHz), both perceived as green light. The background was provided by a white LED. The optical system and measurement procedure details are outlined in (Proc. SPIE 1250215). The luminance of the infrared stimulus was determined using a brightness adjustment method. To evaluate defocusing effects, the procedure was performed with the optimal refractive correction for each subject and with an additional defocusing of -1.00 diopters. Approval for the study was obtained from the Bioethics Committee of the Collegium Medicum, Nicolaus Copernicus University.
Results :
The obtained values of CSF for two-photon vision (2phCSF) under optimal focusing are higher than values of CSF for standard one-photon vision (1phCSF). The average ratio 2phCSF to 1phCSF is higher than 1 (1.4 ± 0.8), indicating the advantage of two-photon vision. The effect of defocusing showed a statistically significant difference for CSFs values for spatial frequency of 24 cpd. The results indicate that defocusing substantially reduces the 1phCSF (22.4 ± 3.4 to 9.4 ± 1.9 for focused and defocused conditions, respectively), while its impact on 2phCSF reduction is insignificant (30.5 ± 10.1 to 23.2 ± 9.3 for focused and defocused conditions, respectively).
Conclusions :
The results demonstrate an advantage in contrast sensitivity for two-photon vision, as it enables the preservation of stimulus quality despite defocusing, compared to one-photon vision. The presented feature of two-photon vision may be relevant in applying this phenomenon in retinal displays.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.