Abstract
Purpose :
A recent study showed that photoreceptors (PRs) appeared to be fluorescently labelled in carriers of choroideremia on AO-ICG imaging, hypothesized to be due to disruption of the outer blood-retinal barrier. Here we show that patterns of fluorescence matching the PRs are clearly visible even in healthy eyes when imaged with AO-ICG.
Methods :
Six healthy participants were imaged with adaptive optics scanning laser ophthalmoscopy (AOSLO) using 795 nm (Δ16 nm) illumination for simultaneous confocal and AO-ICG imaging (emission: 842Δ56 nm). The retina was imaged contiguously from the fovea up to 12° temporally before and at several timepoints following ICG dye injection. Fluorescence and reflectance images were overlaid for qualitative and quantitative comparison. Two graders subjectively evaluated 270 (~140×140µm) images for the appearance of PRs. Power spectral densities were computed to compare the spatial frequency content of each modality.
Results :
The expected pattern of RPE staining was observed on AO-ICG. Additionally, a pattern matching the PRs from the confocal images, was seen across the whole imaged area. PR visibility varied with eccentricity and was seen in the early phase and for up to 24h (Fig.1). Subjectively, PRs were clearly detected in 53% of the images; visibility was lowest in the fovea and most apparent from 3–6°. Power spectral densities displayed matching prominent peaks at a band of spatial frequencies corresponding to the PRs modal spacing. Green circles in Fig. 2 denote a few PRs visible in each modality; yellow arrowheads point to an area of mismatch.
Conclusions :
Fluorescence signals that matched the pattern of the PRs mosaic were observed on AO-ICG in all 6 eyes with presumed intact blood-retinal barriers. This may be due to an imprinting effect from the PRs, like what has been shown previously in autofluorescence imaging of the RPE. Another possibility is that the PRs themselves are labelled by the ICG dye through their interaction with the RPE, however the physiological mechanism remains unknown. We are systematically evaluating and comparing the AF of the cones and underlying RPE in ongoing study and further research is needed to reconcile these findings with previous work.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.