Over the past 5 years, visible light Optical Coherence Tomography (OCT) has emerged as a promising technique for ultrahigh resolution microstructural imaging and depth-resolved imaging of chromophores. In the retina, visible light OCT can simultaneously induce and observe retinal changes during the phototransduction cascade, including bleaching-related absorption changes, as well as intrinsic scattering, cell swelling, and possible longer-term changes in retinal chromophores. Here we investigate outer retinal reflectance changes during visible light OCT in mice to better understand the contributions of these various signals.
All experiments were performed on pigmented (C57BL/6J) and albino (BALB/c) mice in an initially dark-adapted state. There were no consistent reflectance changes in any layers including and proximal to the External Limiting Membrane (ELM). However, reflectance increased in the inner segment / outer segment (IS / OS) junction and outer segments tips (OST) of both strains. Layers distal to the photoreceptors such as the Retinal Pigment Epithelium (RPE), Bruch’s membrane (BM), and choroid showed a consistent increase in pigmented mice and showed no significant change in albino mice. Though our results are qualitatively well-explained by results from photopigment bleaching and intrinsic optical signal experiments in the literature, the time scale of some of the changes observed in our study is too long, which could indicate either signals with a different physiological origin or the need for a more precise model to describe imaging and stimulation using the same beam profile.