Structural integrity of retinal pigment epithelial cells in eyes with age-related scattered hypofluorescent spots on late phase indocyanine green angiography (ASHS-LIA)

Purpose The purpose of this study was to establish that retinal pigment epithelial (RPE) cells take up indocyanine green (ICG) dye following systemic injection and that adaptive optics enhanced indocyanine green ophthalmoscopy (AO-ICG) enables direct visualization of the RPE mosaic in the living human eye. Methods A customized adaptive optics scanning light ophthalmoscope (AOSLO) was used to acquire high-resolution retinal fluorescence images of residual ICG dye in human subjects after intravenous injection at the standard clinical dose. Simultaneously, multimodal AOSLO images were also acquired, which included confocal reflectance, nonconfocal split detection, and darkfield. Imaging was performed in 6 eyes of three healthy subjects with no history of ocular or systemic diseases. In addition, histologic studies in mice were carried out. Results The AO-ICG channel successfully resolved individual RPE cells in human subjects at various time points, including 20 minutes and 2 hours after dye administration. Adaptive optics-ICG images of RPE revealed detail which could be correlated with AO dark-field images of the same cells. Interestingly, there was a marked heterogeneity in the fluorescence of individual RPE cells. Confirmatory histologic studies in mice corroborated the specific uptake of ICG by the RPE layer at a late time point after systemic ICG injection. Conclusions Adaptive optics-enhanced imaging of ICG dye provides a novel way to visualize and assess the RPE mosaic in the living human eye alongside images of the overlying photoreceptors and other cells.

The heterogeneity of individual cells in a tissue has been well characterized, largely using ex vivo approaches that do not permit longitudinal assessments of the same tissue over long periods of time. We demonstrate a potentially novel application of adaptive optics fluorescence microscopy to visualize and track the in situ mosaicism of retinal pigment epithelial (RPE) cells directly in the human eye. After a short, dynamic period during which RPE cells take up i.v.-administered indocyanine green (ICG) dye, we observed a remarkably stable heterogeneity in the fluorescent pattern that gradually disappeared over a period of days. This pattern could be robustly reproduced with a new injection and follow-up imaging in the same eye out to at least 12 months, which enabled longitudinal tracking of RPE cells. Investigation of ICG uptake in primary human RPE cells and in a mouse model of ICG uptake alongside human imaging corroborated our findings that the observed mosaicism is an intrinsic property of the RPE tissue. We demonstrate a potentially novel application of fluorescence microscopy to detect subclinical changes to the RPE, a technical advance that has direct implications for improving our understanding of diseases such as oculocutaneous albinism, late-onset retinal degeneration, and Bietti crystalline dystrophy. An application of fluorescence microscopy is used to visualize and longitudinally track the mosaicism of the retinal pigment epithelial cells in the human eye.

Age-related scattered hypofluorescent spots on late-phase indocyanine green angiography (ASHS-LIA) might represent fundus aging and neutral lipid accumulation. The present study was conducted to determine the association between drusen and ASHS-LIA and to provide further evidence for our hypothesis.