Optical coherence tomography (OCT) has changed diagnostics in ophthalmology by visualizing the morphology of retinal cell layers, which play an important role in human vision. Direct visualization of the activity of these different layers could have an equally strong impact on research and clinical diagnostics. But until recently all attempts to use OCT to image changes of the optical tissue properties that are associated with retinal function (intrinsic optical signals, IOS) were hampered by ocular motion, speckle noise, and limited lateral resolution. Measurements were cumbersome and did not yield straightforward, interpretable physiologic information. Based on a high-speed CMOS camera, full-field swept-source (FF-SS) OCT was developed for in vivo retinal imaging. Within milliseconds, FF-SS-OCT acquires three-dimensional images of the retina which contain information on amplitude and phase of the scattered light virtually free of motion artifacts. Utilizing the phase information, we were able to correct ocular aberrations in order to resolve individual cones and could interferometrically measure sub-wavelength length changes of the photoreceptor outer segments (OS) upon optical stimulation. With this approach, we imaged single cone activity in the living human eye and quantified the photoreceptor response with good accuracy. Currently, the origin of the observed IOS is not completely understood, but there is strong evidence that osmotic effects change the shape of the outer segment. Translating this technology for objective monitoring of photoreceptor activity to clinical applications could have considerable impact in ophthalmology and neurology and might also contribute to basic vision research. This work is an important step to reach the ambitious goal of imaging function of the complete retina with cellular resolution.
Copyright 2019, The Author(s).