Polarization OCT optoretinography: verifying light-induced photoreceptor outer segment shrinkage and subretinal space expansion

Stimulus-evoked intrinsic optical signal (IOS) changes in retinal photoreceptors play a critical role in functional optoretinography (ORG). However, conflicting results regarding light-induced photoreceptor outer segment (OS) elongation and shrinkage have been reported. These discrepancies may stem from the difficulty in reliably identifying OS boundaries, particularly the inner segment/outer segment (IS/OS) junction and OS tip, as well as potential confusion with subretinal space dynamics. In this study, we employed a polarization-resolved full-field swept-source optical coherence tomography (FF-SS-OCT) system capable of recording both parallel-polarization and cross-polarization OCT signals. Parallel polarization OCT is optimized for detecting ballistically reflected photons from layer-like boundaries, while cross-polarization OCT predominantly captures multiply scattered photons. This distinction allows parallel-polarization OCT to minimize the effect of multiply scattered photons on OCT band quantification, facilitating the confirmation of light-driven OS shrinkage and subretinal space expansion in the human retina.