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Charles E Granger, David R Williams, Ethan A. Rossi; Near-infrared autofluorescence imaging reveals the retinal pigment epithelial mosaic in the living human eye. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3429.
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© ARVO (1962-2015); The Authors (2016-present)
Individual retinal pigment epithelial (RPE) cells have previously been imaged using short wavelength autofluorescence (SWAF) excitation of lipofuscin in adaptive optics scanning light ophthalmoscopy (AOSLO). Fluorescence imaging of RPE cells at longer wavelengths could be safer. Near-infrared autofluorescence (NIRAF), thought to originate from melanin in the RPE and choroid, has been observed in commercial confocal scanning laser ophthalmoscopy but the mosaic has not been resolved in vivo at these wavelengths. Imaging RPE cells via fluorophores in the NIR could provide new information about RPE morphology in the living eye.
A near-infrared superluminescent diode (790 nm cutoff) was used for simultaneous NIRAF excitation and reflectance imaging in AOSLO. The light from the eye was split into reflectance and NIRAF (805–900 nm) channels. Automated placement of the NIRAF detector and confocal pinhole maximized signal collection. NIRAF images were acquired at many retinal locations in five normal human eyes and one with early drusen. Excitation powers of 60–120 µW were used for 50–100 s exposures over a 1.5° square field of view. NIRAF images were co-registered using the reflectance channel as a motion reference. In three subjects, NIRAF images were compared to previously acquired SWAF images.
High resolution NIRAF images revealed individual RPE cells in all eyes, at the fovea and extending to the most distant eccentricities tested (~15 degrees). Cells appeared similar to SWAF images with a dark center and bright border. Cells were co-localized in each modality, though NIRAF permitted additional cells to be seen beneath retinal vasculature (Fig. 1).
Individual RPE cells can be imaged with NIRAF in AOSLO at typical reflectance imaging light levels. This method reduces many of the challenges associated with SWAF RPE imaging including light safety concerns and the need for chromatic aberration compensation. Additional cells may be seen beneath retinal vasculature in NIRAF due to lower absorption of longer wavelengths by blood. NIRAF imaging may allow improved clinical implementation of RPE cell imaging in normal and diseased eyes, and additionally provide a complementary view of fluorophores within cells.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
SWAF and NIRAF RPE images from separate time points at 12° temporal. Cell visibility is increased beneath vasculature (arrows) in NIRAF.
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