Abstract
Purpose :
The contrast sensitivity function for two-photon vision (2phCSF) has not yet been thoroughly characterized. First attempts have been made to measure contrast sensitivity for two-photon vision (IOVS (63)(2022) pp.2234 – F0442). This study aims to extend the research, complete the data on 2phCSF and compare it to standard, one-photon CSF (1phCSF).
Methods :
This study involved six healthy volunteers (4W, 2M, aged 24–43) without diagnosed pathologies of the visual system. CSFs were measured for eight spatial frequencies in the range of 1–24 cpd using the tumbling E optotype (in a four-alternative forced-choice procedure). The optotype was projected onto the retina by scanning with a pulsed 520 nm or 1040 nm laser beam (200 fs, 76 MHz), both perceived as green. The background was obtained with a white LED. The optical system and measurement procedure are detailed in (Proc. SPIE 1250215). Since the presented optotype was chromatic, the additional 1phCSF measurements were made using a standard LCD screen, which also displayed the green optotype on a white background. Moreover, for further investigation of CSFs, measurements were made for one- and two-photon stimuli on a green background (520 nm). The study was approved by the Bioethics Committee of the Collegium Medicum, Nicolaus Copernicus University.
Results :
The 2phCSFs were normalized to the values of 1phCSFs for a spatial frequency of 3 cpd. Results demonstrate a significantly broader dynamic range for two-photon stimulus than its one-photon counterpart (for visible and infrared beams are 2.54 log and 3.16 log, respectively). Moreover, the shape of 2phCSF differs significantly from 1phCSF: the 1phCS exhibits maximum value in the range of 1–4 cpd, while 2phCSF decreases linearly with increasing spatial frequency from the maximal value at 1 cpd. The tendency reproduces for each investigated subject. Using the stimuli on a green background also resulted in a broader dynamic range for 2phCSF than for 1phCSF (2.94 log and 0.75 log, respectively).
Conclusions :
The presented results confirm the conclusions from the previous study that 2phCSF exhibits a broader range than 1phCSF. It may be related to the quadratic dependence of stimulus brightness on laser beam power and precise stimulation of retinal photoreceptors, which are the features of two-photon vision. Further studies of 2phCSF including measurements with chromatic letter stimuli (green/red and blue/yellow) are planned.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.