Eyeworld

30 March 2018 EW NEWS & OPINION Research highlight by Liz Hillman EyeWorld Staff Writer assumptions that go into research being done on the retina." "It has been an accepted 'truth' that rods do not contribute to daylight vision, something you can find in essentially every textbook; there are notable exceptions where this is not stated in such absolute terms," he said. "As a result, exper- imental (or medical) observations are being interpreted under those as- sumptions, and conclusions drawn from such observations may not be entirely correct. At the very least, our results show that one has to be much more careful with the inter- pretation of vision experiments in bright conditions." While there might not be any direct clinical implications for these findings, Dr. Münch said the find- ings could support research of the biochemical properties that could be supporting rod function under bright light. "This would provide potential targets for improving daylight rod vision to help patients suffering from achromatopsia," Dr. Münch said, adding that it would remain to be seen if such a treatment would be preferable over other forms of treatments. Dr. Münch said future research could also include psychophysical tests in human participants with impaired cones to see if any contri- butions from rods are detectable. "This would provide direct evi- dence that our findings in a mouse retina reflect a similar phenomenon in humans," Dr. Münch said. EW Reference 1. Tikidji-Hamburyan A, et al. Rods progres- sively escape saturation to drive visual re- sponses in daylight conditions. Nat Commun. 2017;8:1813. Editors' note: Dr. Münch has no finan- cial interests related to his comments. Contact information Münch: thomas.muench@gmail.com intensity and the duration of ex- posure," Tikidji-Hamburyan et al. wrote. "Surprisingly and counter-in- tuitively, both higher background intensity and prolonged exposure result in reduced saturation, i.e., in more robust rod-driven signaling." Overall, Dr. Münch said these findings present "a change in initial exposure to higher irradiances with recovery over time. Interest- ingly, they noted faster recovery of contrast sensitivity of the rod cells at brighter levels of light. "Together, our data show that the presence and reappearance of rod responses depends not simply on the background intensity, but on the interaction between background Study finds that rod cells in mice retinas contribute to daylight vision I t's one of the first things taught about the visual system in even the most basic of science classes: Cone photoreceptors provide bright light and color vision, while rod photoreceptors contribute to vision in low light conditions. New research from the Universi- ty of Tübingen, Germany, however, shows rod photoreceptors, at least in mouse models, still function in bright light. 1 Thomas Münch, PhD, head of research, Department of Retinal Circuits and Optogenetics, Werner Reichardt Centre for Integrative Neuroscience (CIN), University of Tübingen, who led the group of researchers, explained that the research initially stemmed from observations made of mice without functional cones. These coneless mice showed stable and easily observable light responses in bright conditions. "There are only two possible explanations for this observation: Either these mouse lines are 'wrong' in the sense that they do have func- tional cones after all, or the respons- es come from rods. Our experiments showed that the second answer was right," Dr. Münch said. Tikidji-Hamburyan et al. de- signed an experiment to "explicitly define the limits of rod vision" by re- cording electrophysiological activity in isolated mouse retina ex vivo, and in mouse visual brain areas in vivo, over a wide range of light intensities. In all cases, the researchers found robust light-driven responses—also in bright light conditions—even though these mice lacked functional cone cells. In further experiments on mice with functional cone cells, they could confirm the function of the rod cells in bright light conditions. The researchers observed reduced contrast sensitivity upon New research breaks with widely held 'truth' about rod photoreceptors " At the very least, our results show that one has to be much more careful with the interpretation of vision experiments in bright conditions. " —Thomas Münch, PhD

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