  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.
