Abstract
Retinal pigmented epithelial (RPE) cells are essential for maintaining normal visual function, especially in their role in the visual cycle, and are thought to be one of the first cell classes affected by age-related macular degeneration (AMD). Clinical imaging systems routinely evaluate the structure of the RPE at the tissue level, but cellular level information may provide valuable RPE biomarkers of health, aging and disease. In this exploratory study, participants were imaged with 795 nm excitation in adaptive optics scanning laser ophthalmoscopy (AOSLO) to observe the microstructure of the near-infrared autofluorescence (AO-IRAF) from the RPE layer in healthy retinas and patients with AMD. The expected hexagonal mosaic of RPE cells was only sometimes seen in normal eyes, while AMD patients exhibited highly variable patterns of altered AO-IRAF. In some participants, AO-IRAF structure corresponding to cones was observed, as we have demonstrated previously. In some AMD patients, marked alterations in the pattern of AO-IRAF could be seen even in areas where the RPE appeared relatively normal in clinical imaging modalities, such as spectral domain optical coherence tomography (SD-OCT). AO-IRAF imaging using AOSLO offers promise for better detection and understanding of early RPE changes in the course of AMD, potentially before clinical signs appear.
Highlights
The human retina naturally emits light as it is absorbing light due to its intrinsic autofluorescence (AF)
Fluorophore compartmentalization within the retinal pigmented epithelial (RPE) may be altered in age-related macular degeneration (AMD), making it difficult to see the same type of structure of the RPE cells in the AO-infrared autofluorescence (IRAF) images compared to healthy volunteers
It is likely that natural age-related alterations in the relative abundance and composition of RPE AF organelles impacts the efficacy of different AF wavelength bands for visualizing RPE cells across the lifespan. This observational study demonstrates the potential of AO-IRAF imaging applied to patients with AMD
Summary
The human retina naturally emits light as it is absorbing light due to its intrinsic autofluorescence (AF). Fundus autofluorescence (FAF) has become routine for evaluating disease status and monitoring progression in certain pathologies because of its potential to reveal retinal pigment epithelium alterations that are difficult to distinguish using other imaging modalities[4,5,6] It has been capitalized on in adaptive optics scanning laser ophthalmoscopy (AOSLO) to image individual retinal pigmented epithelial (RPE) cells[7,8,9]. Though it has been suggested that AO-IRAF offers complementary information to SWAF26 and may be a promising alternative for studying early cellular alterations to the RPE in diseases such as AMD, to date it has only been visualized at a cellular level in a small number of eyes in a limited age range and in only a few diseased eyes[9,27,28] It remains unknown whether AO-IRAF can effectively and routinely be used to image RPE cells in normal eyes or eyes with AMD. Optical coherence tomography (OCT) consistently visualizes all the retinal layers in cross-section but despite its impressive axial resolution (5–10 μm), individual cells cannot be distinguished in the RPE layer without AO (due to 10–20 μm lateral resolution) and substantial volumetric averaging[35,36]
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