In-vivo optophysiology in rodent eyes using phase-sensitive optical coherence tomography

Recently, there has been vast interest in probing photoreceptor dynamics using optical coherence tomography (OCT). Most successful demonstrations implemented adaptive optics or digital adaptive optics to resolve individual cones or rods in human subjects. Here we use phase information to trace the photoreceptor response in rodents using an ultrahigh-resolution, phase-sensitive, spectral-domain OCT. Brown Norway rats (6-14 weeks) were sedated using a ketamine and xylazine cocktail. Repeated scans were registered by a phase-restoring subpixel motion correction algorithm to isolate the bulk motion, and two hyperreflective bands (inner segment/outer segment junction – IS/OS; outer segment tip + retinal pigment epithelium + Bruch's membrane) were segmented automatically. As a result, two types of nanoscale signals (biphasic Type-I and monophasic Type-II) were detected with a clear separation in depth. We tested the repeatability, scotopic stimulus strength dependency, and photopic background intensity dependency. Besides, we demonstrated enface mapping of the ORG signals in a wide field of 20°, analogous to the multifocal electroretinogram but with a much higher resolution, revealing the spatial distribution of the outer retina function. This method could be extended to study animal models with photoreceptor degeneration and clinical studies to investigate early photoreceptor dysfunction with high spatiotemporal resolution.