Retinal intrinsic optical signal and optical coherence tomography

The amount of light backscattered from neural tissues changes as a function of activation and is the basis of intrinsic optical signal (IOS). Typically IOS is observed by looking at darkfield scatter with a CCD camera. The retina is a calculating portion of the central nervous grey matter with an optical quality window, and is likewise easily stimulated optically. Therefore the retina makes a natural model for observing neural interactions with optical tools. Optical coherence tomography (OCT) is an imaging modality that provides depth resolved maps of the amount of light backscattered from tissue that has wide clinical use for observing structural defects associated with ophthalmic disease. It is therefore also natural to use OCT as means to observe intrinsic optical signal in the retina. Indeed, OCT has recently been used to observe an increase in backscatter at the level of the outer photoreceptor segment after bleaching light stimulation in an excised rabbit retina. We are currently attempting to translate this result towards a diagnostic technique for photoreceptor dysfunction in human patients. Currently patient motion and physiological noise present barriers that must be overcome with increases in technological and experimental sophistication. This proceeding reviews current understanding of retinal intrinsic optical signal and discusses its measurement challenge.