Interferometric imaging of the reversible rhodopsin dynamics in the living rat eye.

Vision begins with conformational changes in photopigments. The associated electrical signature, called an early receptor potential (ERP), in rods is limited to contribution of a small fraction of rhodopsin embedded in plasma membrane. Optoretinography (ORG), using phase-sensitive optical coherence tomography, detects nanoscale deformations of retinal cells associated with physiological processes. In previous ORG studies, focused primarily on cones, deformation related to ERP was largely obscured by osmotic swelling and long stimuli. Here, we demonstrate a robust electromechanical signature of photoisomerization in rods. A green flash induces a sub-millisecond contraction of the outer segments by hundreds of nanometers, while a subsequent UV flash reverts the activated molecules, producing an opposite response of similar magnitude. ORG surpasses the sensitivity of electrical methods by integrating the response across all the discs in rod outer segments and it opens the door to fundamental studies of visual transduction in-vivo and to more specific clinical diagnosis.