Figure 3. Accumulation of cationic and neutral liposomes was observed with the scanning laser ophthalmoscope (SLO) in vivo. Cationic liposomes (CL)-indocyanine green (ICG), CL-Oregon green (OG), or neutral liposomes labeled with OG were applied intravenously at d1, d5, d10, or d14 after laser treatment. SLO images were recorded for each laser choroidal neovascularization (CNV) 60 min later. A: One representative CNV is shown for each time point and for each of the formulations tested. The CL-ICG images are taken from the same CNV in one mouse, and the corresponding infrared (IR) images are shown for comparison. The other images are taken from different animals. Although neutral liposomes did not accumulate within the CNV, CL-OG was found from d10 onwards and CL-ICG starting from d5. B: The ratio of accumulation of liposomes in the CNV to the control area was calculated for each CNV as described in the methods section. The means and the standard errors of the mean are shown. Values for CL-OG at d10 and d14 and for CL-ICG at d5, d10, and d14 were significantly higher compared to those of neutral liposomes. Data are means obtained from five mice. Error bars indicate SEM, and asterisks indicate statistical significance (p<0.05 as compared to d1). C: Absorption spectrum of mouse RPE. After the retina as removed, the RPE was scraped out, homogenized by pipetting, and diluted in water. Transmission is higher at longer wavelengths. The OG emission was detected at 530 nm and that of ICG at 830 nm. The murine RPE absorption was about twice as high at 530 nm as at 830 nm. This gives an estimate of the reduction of fluorescence emitted by fluorophores when they are located behind the RPE in vivo and is one of the reasons why ICG is more suitable for diagnostics of sub-RPE lesions than OG or fluorescein.