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Visual acuity in two-photon infrared vision

Pablo Artal, Silvestre Manzanera, Katarzyna Komar, Adrián Gambín-Regadera, and Maciej Wojtkowski

Open Access Open Access

Abstract

Humans can detect infrared light at wavelengths over 1000 nm, perceived as visible light of the corresponding half wavelength. This is due to a two-photon (2P) absorption process, which requires sufficiently large amounts of luminous energy. For safety reasons, this energy must be delivered by pulsed light sources well focused in the retina. Although this effect has been known for several decades, the spatial properties of 2P vision in comparison to normal vision have not yet elucidated. We have developed a new experimental system to measure, for the first time, to the best of our knowledge, visual acuity mediated by 2P absorption and compare it against that with visible light. The spatial resolution of 2P infrared vision is the same as in normal visible light. However, the use of 2P infrared vision may have some future potential applications, for example, in permitting vision in those cases with opaque optical media to visible wavelengths while keeping some transparency in the infrared.

© 2017 Optical Society of America

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Supplementary Material (2)

NameDescription
Data File 1       VA data
Supplement 1       Exposure safety limits calculations

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Figures (3)
Fig. 1.
Fig. 1. Schematic diagram of the apparatus. Either a visible CW (cwL) or an IR pulsed (fsL) laser is used to deliver visual stimuli to the subject’s eye by means of a galvo mirror system (xyG). Double-pass images are acquired using high-sensitivity (CAM1). Additional elements are: DM, dichroic mirror; A1–A3, apertures; L1–L5, achromatic doubles; BS, beam splitter; tL, trial lenses; NDF, neutral density filter; C-Pol, crossed linear polarizers; CAM2, alignment camera.

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Fig. 2.
Fig. 2. On the left, the Y axis (solid lines) is represented by the averaged visual acuity across subjects measured in visible and IR light as a function of defocus. Values are shown normalized to the maximum. All defocus values are relative to the focus position where the best VA is achieved in visible light. Error bars stand for intersubject variability. See Data File 1 for underlying values. On the right Y axis (dashed lines and open symbols), the averaged-across-subjects through-focus maximum intensity in the recorded double-pass images.

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Fig. 3.
Fig. 3. Example of the recorded double-pass images. They correspond to the best focused images recorded from subject #4 in (A) visible and (B) IR. They are normalized to the maximum. The width of each scale bar represents the corresponding Airy disk diameter for the wavelength and pupil size used (4.6 and 4.4 min of arc for visible and IR, respectively).

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