Abstract
Purpose :
Vision in the infrared (IR) is produced by a two-photon (2P) absorption process. Since this is a nonlinear phenomenon, it is expected to occur only at the very center of the focused light on the retina, resulting in a smaller effective PSF that should enhance resolution. Visual acuity (VA) in 2P vision was compared with that in visible light (Artal et al., Optica, 2017), but no significant difference was found, probably because a small pupil was used. The aim of this study is to develop an adaptive optics (AO) system to operate in conjunction with a 2P vision stimulator.
Methods :
A dedicated research prototype was designed, built and tested. The illumination source (FL-1064-nano, CNI, Chanchung, China) delivers pulsed light at the wavelength of 1064 nm with a pulse width that can be tuned from 5 to 100 ns and with repetition frequencies from 100 to 1000 kHz. To produce the visual stimulus, the light beam is scanned on the retina by means of a dual-axis scanning galvo system (GVS002, Thorlabs Inc., Newton, NJ). The aberrations of the subject’s eye were measured by a Hartmann-Shack sensor and the correction is performed by means of a spatial light modulator (SLM), specially designed to operate in the NIR part of the spectrum (Pluto, Holoeye Photonics AG, Germany). In addition, a motorized Badal optometer is used to correct defocus, partly releasing the SLM.
Results :
The used IR light source has shown to be able to elicit the 2P vision with a pulse duration of 5 ns. The AO part of the instrument was first operated in an artificial eye. Images of the retinal images were recorded after using trial lenses to induce different levels of defocus and astigmatism at different orientations. The instrument was able to produce AO corrections up to a 6-mm pupil diameter. The system was subsequently also demonstrated in healthy participants with normal levels of aberrations where 2P vision was produced with and without aberration correction.
Conclusions :
We developed adaptive optics aberration corrector to provide 2P vision with near-diffraction limited PSFs at large pupil diameters. This instrument allows further investigation of the limits of the spatial resolution of the 2p vision mechanism. The capabilities of the IR light source, in terms of pulse width and pulse repetition rate, will also allow us to explore other domains of 2P vision.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.