Retinal pigment epithelium (RPE) cells are vital to health of the outer retina, however, are often
compromised in ageing and ocular diseases that lead to blindness. Early manifestation of RPE disruption
occurs at the cellular level, but while in vivo biomarkers at this scale hold considerable promise, RPE
cells have proven extremely challenging to image in the living human eye. Recently we addressed this
problem by using organelle motility as a novel contrast agent to enhance the RPE cell in conjunction with
3D resolution of adaptive optics-optical coherence tomography (AO-OCT) to section the RPE layer. In
this study, we expand on the central novelty of our method – organelle motility – by characterizing the
dynamics of the motility in individual RPE cells, important because of its direct link to RPE physiology.
To do this, AO-OCT videos of the same retinal patch were acquired at approximately 1 min intervals or
less, time stamped, and registered in 3D with sub-cellular accuracy. Motility was quantified by an
exponential decay time constant, the time for motility to decorrelate the speckle field across an RPE cell.
In two normal subjects, we found the decay time constant to be just 3 seconds, thus indicating rapid
motility in normal RPE cells.