Abstract
Purpose :
To evaluate the status of heterogeneously labeled retinal pigment epithelial (RPE) cells following repeated uptake of indocyanine green dye (ICG) (PMID 27564519), categorized according to the degree to which cells fluoresce (bright cells, which are thought to have more ICG, and dark cells, less ICG). The natural variability in fluorescence provides an opportunity to evaluate whether bright cells are more likely to drop out possibly due to preferential ICG uptake.
Methods :
Ten subjects (17 healthy eyes) were longitudinally followed using late phase adaptive optics enhanced indocyanine green (AO-ICG) imaging performed after i.v. injection of ICG (25 mg administered at each visit, for up to 5 visits). Time intervals between visits varied from 2 months to 2 years with the longest follow-up period extending out to 6 years. For each image (n=45), ~100 foveal RPE cells were semi-automatically identified and validated by two graders. RPE density was compared across visits to monitor for any signs of RPE dropout. The average intensity of each identified cell was calculated based on the cell’s corresponding Voronoi neighborhood. The distribution of bright and dark cells was examined to evaluate whether there were any changes in the amount of bright or dark cells across visits.
Results :
Overall, there was no evidence that ICG uptake into RPE cells was associated with RPE cell drop out based on RPE density measurements. RPE density was not significantly different between the first and last visits (p=0.14, two-tailed paired t-test) and there was no apparent relationship between cumulative ICG dose compared to the percent change in RPE density relative to the baseline visit (p=0.36, ANOVA on univariate linear regression). The heterogeneous pattern of bright and dark cells was consistently re-established with each repeated administration of ICG, as has been previously reported (PMID 30895942). Histograms of fluorescence intensity tracked across visits revealed no apparent differences in either the location of the histogram peak nor the shape (skewness) (p=0.07, p=0.67, two-tailed paired t-test, respectively).
Conclusions :
Repeated uptake of ICG into RPE cells does not appear to lead to changes in RPE structure, based on in vivo longitudinal assessments performed up to a period of 6 years.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.