Human infrared Vision is triggered by two-photon chromophore isomerization

Grazyna Palczewska, Frans Vinberg, Patrycjusz Stremplewski, Martin P. Bircher, David Salom, Katarzyna Komar, Jianye Zhang, Michele Cascella, Maciej Wojtkowski, Vladimir J. Kefalov, Krzysztof Palczewski

Research output: Contribution to journalArticlepeer-review

78 Scopus citations


Vision relies on photoactivation of visual pigments in rod and cone photoreceptor cells of the retina. The human eye structure and the absorption spectra of pigments limit our visual perception of light. Our visual perception is most responsive to stimulating light in the 400- to 720-nm (visible) range. First, we demonstrate by psychophysical experiments that humans can perceive infrared laser emission as visible light. Moreover, we show that mammalian photoreceptors can be directly activated by near infrared light with a sensitivity that paradoxically increases at wavelengths above 900 nm, and display quadratic dependence on laser power, indicating a nonlinear optical process. Biochemical experimentswith rhodopsin, cone visual pigments, and a chromophore model compound 11-cis-retinyl-propylamine Schiff base demonstrate the direct isomerization of visual chromophore by a two-photon chromophore isomerization. Indeed, quantum mechanics modeling indicates the feasibility of this mechanism. Together, these findings clearly show that human visual perception of near infrared light occurs by twophoton isomerization of visual pigments.

Original languageEnglish
Pages (from-to)E5445-E5454
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number50
StatePublished - Dec 16 2014


  • Multiscale modeling
  • Rhodopsin
  • Transretinal electrophysiology
  • Two-photon absorption
  • Visual pigment


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