Temporal Changes Of Backscattered Intensity From Different Interfaces Of Cone Photoreceptors Observed In Vivo With SLO/OCT

Abstract

Purpose: : The aim of this study was to investigate temporal changes in the backscattered intensity observed in vivo within the junction between inner and outer segments of cone photoreceptors (IS/OS), the end tips of photoreceptors (ETPR) and the retinal pigment epithelium (RPE).

Methods: : Measurements were taken with a transverse scanning optical coherence tomography (OCT) /scanning laser ophthalmoscope (SLO) instrument. The system is capable to provide 3D information of the human cone photoreceptors with negligible eye motion artifacts due to an implemented 3D motion correction. Short term (every hour within 7 hours, from 9 a.m. to 4 p.m.) and long term (every 24 hours up to 96 hours) changes were investigated in healthy subjects at ~4 degrees eccentricity from the fovea.

Results: : Our short term measurement shows randomly varying intensities of individual cones in the time series of the SLO images and the depth integrated OCT images (intensity fluctuations of 50%). The 3D information provided by OCT reveals that most cones show intensity fluctuations in both photoreceptor reflection sites, the IS/OS and the ETPR layer. Interestingly these fluctuations seem to be independent from cone to cone and within the same cone from IS/OS to ETPR. Distinct reflections at the transverse position of a cone within the RPE layer could be observed. These reflections occur randomly with time below different cones. In the long term measurements intensity fluctuations were much more pronounced.

Conclusions: : The OCT/SLO system is able to provide an in vivo investigation of exactly the same retinal location with cellular resolution over several days. Intensity fluctuations in the IS/OS boundary are observable. We assume, that these might be caused by the formation of new discs at the IS/OS boundary. Intensity fluctuations observed at the ETPR could be explained by different status of the disc shedding process. Backscattered light from migrating phagosomes or pigments might cause the bright reflections within the RPE.

Keywords: imaging/image analysis: non-clinical • photoreceptors • retinal pigment epithelium