Delayed near-infrared analysis permits visualization of rodent retinal pigment epithelium layerin vivo

Abstract

Patches of atrophy of the retinal pigment epithelium (RPE) have not been described in rodent models of retinal degeneration, as they have the clinical setting using fundus autofluorescence. We hypothesize that prelabeling the RPE would increase contrast and allow for improved visualization of RPE loss in vivo. Here, we demonstrate a new technique termed “delayed near-infrared analysis (DNIRA)” that permits ready detection of rat RPE, using optical imaging in the near-infrared (IR) spectrum with aid of indocyanine green (ICG) dye. Using DNIRA, we demonstrate a fluorescent RPE signal that is detected using confocal scanning laser ophthalmoscopy up to 28 days following ICG injection. This signal is apparent only after ICG injection, is dose dependent, requires the presence of the ICG filters (795/810 nm excitation/emission), does not appear in the IR reflectance channel, and is eliminated in the presence of sodium iodate, a toxin that causes RPE loss. Rat RPE explants confirm internalization of ICG dye. Together with normal retinal electrophysiology, these findings demonstrate that DNIRA is a new and safe noninvasive optical imaging technique for in vivo visualization of the RPE in models of retinal disease.

Fundus autofluorescence (FAF) non-invasively identifies chorioretinal toxicity in a rat model of retinal pigment epithelium (RPE) damage

“…3C and D). Consistent with our previous observations, we noted a slight decrease in the ERG responses in the control group over time (Pankova et al, 2014). This decrease is not considered biologically significant.…”

In Vivo Imaging of the Human Retinal Pigment Epithelial Mosaic Using Adaptive Optics Enhanced Indocyanine Green Ophthalmoscopy

“…The mechanism for this differential fluorescence remains to be explored, as it is currently unknown whether this is due to differential uptake of ICG dye or due to quenching from intrinsic pigments such as melanin, which has a broad absorption spectra that may be different in vivo than in vitro. 30 Interestingly, the heterogeneity of the prolonged ICG signal that we observed in humans has also been reported in rats 5 and considerable cell-to-cell heterogeneity within the RPE mosaic has been shown. 31 Images of the AO-ICG signal presented in this paper will form the basis for future investigations to explore the interactions between ICG and RPE at the cellular level.…”

“…Histologic evidence has suggested that there may be accumulation of ICG dye in the late phase within retinal pigment epithelial (RPE) cells. 4,5 To explore this phenomenon, we further investigated whether ICG could be used for imaging the RPE cells in the living human eye with adaptive optics (AO) ophthalmoscopy.…”

Hydrophobically-modified poly(vinyl pyrrolidone) as a physically-associative, shear-responsive ophthalmic hydrogel

“…10c), with no abnormal hypo-or hyperfluorescence observed. Further, owing to poor reflectivity of the RPE monolayer in the rodent eye (Pankova et al, 2014), delayed near infrared analysis (DNIRA) was used to confirm that the RPE layer remained normal following polymer treatment (Fig. 10d).…”

“…Wavelengths of light included blue spectrum fluorescence (fundus autofluorescence, FAF, at 488/510 nm excitation/emission), red-free, and infra-red reflectance (820 nm). Delayed near infrared analysis (DNIRA, at 790/830 nm excitation/ emission) was also applied to better visualize the RPE layer in vivo (Pankova et al, 2014). To enable DNIRA, indocyanine green (ICG; Cardiogreen; SigmaeAldrich, Oakville, Canada) at a dose of 0.35 mg/kg was administered via tail vein using a 24-gauge catheter three days prior to the baseline assessment.…”