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HaeWon Jung, Tao Liu, Jianfei Liu, Johnny Tam; Adaptive optics assessment of choriocapillaris perfusion and its effect on the accumulation of indocyanine green dye in the overlying retinal pigment epithelium. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4638. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Using adaptive optics, the choriocapillaris and retinal pigment epithelium (RPE) can be visualized based on the initial passage of indocyanine green (ICG) dye through the vasculature and subsequent accumulation of ICG in the RPE. However, whether the choriocapillaris has an effect on dye accumulation in the RPE remains to be explored.
Adaptive optics enhanced indocyanine green (AO-ICG) ophthalmoscopy was used to image eyes in 7 healthy subjects (age 22-52 years). To explore relationships between choriocapillaris perfusion and ICG dye accumulation in the RPE, the fovea was sequentially imaged (during injection and following clearance of ICG from the vasculature). As we showed previously, rapid uptake of ICG into the RPE during the injection phase hinders visualization of choriocapillaris, but it is possible to remove the RPE portion of the signal by comparing the AO-ICG signal across time to generate a choriocapillaris image. This image was further improved by normalizing the AO-ICG signal to simultaneously-captured and co-registered darkfield images.
In all subjects, we observed a sharp rise and fall of the AO-ICG signal lasting 15-20 seconds, which we interpret to be the passage of the ICG dye bolus. In some subjects, the bolus appeared to recirculate a second time leading to a smaller, broader rise and fall of the AO-ICG signal. The time interval between these two peaks (recirculation time) was measured to be 18.4±3.3 seconds (mean±SD; n=5 subjects). In AO-ICG images of choriocapillaris, we observed dark hypofluorescent regions corresponding to pores between vessels which were measured to be 21.3±1.8 µm (mean±SD; n=7), consistent with the values from histology (5-40 µm). Categorization of late-phase AO-ICG images of the RPE into regions above pores vs. above choriocapillaris vessels revealed a small but significant difference in ICG signal intensity (n=7; p<0.05). Surprisingly, the cells above pores were on average 7.4% brighter than those on top of vessels.
The dynamic passage of ICG dye through the choriocapillaris and into the RPE presents a unique opportunity to directly visualize the delivery and uptake of an extrinsic agent through a vascular system into an epithelial layer. Disruptions to this normal physiological phenomenon may reveal effects of disease on the RPE-choriocapillaris complex.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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