Abstract
Purpose :
Adaptive optics enhanced indocyanine green (AO-ICG) imaging can be used to visualize the natural cell-to-cell heterogeneity that exists within retinal pigment epithelial (RPE) cells in the living human eye (IOVS 2016;57:4376-4384). The robustness, long-term stability, repeatability, and clinical applicability of this signal remains to be explored.
Methods :
Following intravenous injection of indocyanine green dye, AO-ICG imaging was carried out to visualize the RPE from 13 healthy subjects (34.7+/-9.9 years, mean+/-SD) and 1 patient with Bietti crystalline dystrophy. To characterize dynamic changes in the signal, sequential imaging was performed at various timepoints after injection: 0-20 minutes (n=3 subjects), 2 hours (n=13), and 2-4 days (n=2). A repeat injection was performed 3-12 months later to explore whether the same pattern would be observed (n=5). Foveal RPE average cell spacing was quantified using a semi-automated approach which detects regions of uniform intensity.
Results :
The AO-ICG RPE signal was robust and observed in every healthy eye imaged (22 eyes; baseline imaging confirmed absence of signal prior to injection). Sequential imaging revealed that the distribution of dye in the RPE varied initially but stabilized 10-15 minutes after injection (n=3). Subsequently, the overall pattern weakened but remained relatively stable until 2-4 days. Interestingly, a repeat injection both 3-4 months later (n=3) and 1 year later (n=2) showed that the same general pattern of intensity was maintained, suggesting that this pattern is an intrinsic property of the tissue. Although the dimensions of foveal RPE cells were similar across healthy eyes, foveal cells in the patient with Bietti crystalline dystrophy appeared to be significantly enlarged (average cell spacing in 22 eyes from 13 healthy subjects: 14.6+/-1.5 µm, mean+/-SD, compared to 22.9 µm in the patient, z-score=5.49).
Conclusions :
AO-ICG can be used to visualize, quantify, and track the RPE over multiple timepoints in the living human eye. The observed pattern appears to be a robust intrinsic property of the tissue and remains relatively stable in the late phase, even across repeated injections. This provides a unique opportunity for assessment and longitudinal tracking of the RPE in disease.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.