In vivo optical imaging of physiological responses to photostimulation   in human photoreceptors
  Non-invasive functional imaging of molecular and cellular processes of vision is expected to have immense impact on research and clinical diagnostics. Although suitable intrinsic optical signals (IOS) have been observed ex vivo and in immobilized animals in vivo, it was so far not possible to obtain convincing IOS of photoreceptor activity in humans in vivo. Here, we observed spatially and temporally clearly resolved changes in the optical path length of the photoreceptor outer segment as response to an optical stimulus in living human. To obtain these changes, we evaluated phase data of a parallelized and computationally aberration-corrected optical coherence tomography (OCT) system. The non-invasive detection of optical path length changes shows the neuronal photoreceptor activity of single cones in living human retina, and, more importantly, it provides a new diagnostic option in ophthalmology and neurology and could give new insights into visual phototransduction in humans. 
Dierck Hillmann, Hendrik Spahr, Clara Pf\"affle, Helge Sudkamp, Gesa   Franke, Gereon H\"uttmann
physics.med-ph physics.optics