Toward Organelle Motility as a Functional Biomarker of Retinal Pigment Epithelium Health

The purpose of this study was to quantify characteristics of retinal pigment epithelium (RPE) organelle motility in human subjects across the temporal (T) macula.

In 11 healthy volunteers (HVs), we used high-speed adaptive optics-optical coherence tomography (AO-OCT) to image RPE cells from the fovea to 12°T. Organelle motility was calculated in the apical, middle, and basal layers as the time constant (τ) of the exponentially decaying speckle decorrelation function normalized to the photoreceptor layer. We imaged 7 HVs on 3 different days at the fovea and 7.5°T to characterize motility repeatability. We imaged 4 HVs on 2 systems with 830 nm and 1060 nm source wavelengths at 7.5°T to explore motility wavelength dependence.

Across the temporal macula, τ decreased from 15.3 (±2.4) to 10.9 (±2.7) seconds (-0.33 seconds/degrees) for the apical RPE, decreased from 9.4 (±1.8) to 8.5 (±1.9) seconds (-0.11 seconds/degrees) for the middle RPE, and was nearly constant (-0.05 seconds/degrees) at 6.7 (±1.0) seconds for the basal RPE at 1060 nm. Motility repeatability was moderate (coefficient of variance [CV] = 10.7% for all subjects and locations). At all RPE layers, τ measured shorter at 830 nm (apical = 6.8 ± 2.2, middle = 4.8 ± 1.0, and basal = 3.8 ± 0.7 seconds) compared with 1060 nm (apical = 10.4 ± 2.8, middle = 6.5 ± 1.6, and basal = 5.0 ± 1.1 seconds, P < 0.005).

RPE organelle motility varies across the macula and cell depth. Our normative dataset will aid future studies of RPE-related retinal pathology.

AO-OCT measured organelle motility is a potential functional biomarker of RPE cell health and ocular disease pathophysiology.