Purpose: To visualize retinal ganglion cells (RGCs) and their gradual loss in the living mouse.
Methods: With the use of B6.Cg-Tg(Thy1-CFP)23Jrs/J mice, which express cyan fluorescent protein (CFP) in RGCs, and a commercially available mydriatic retinal camera attached with a 5 million-pixel digital camera to visualize RGCs in vivo, the authors recorded fundus photographs longitudinally in the ischemia reperfusion model group and the untreated group to evaluate longitudinal changes in the number of RGCs in experimental models. Moreover, RGCs expressing CFP were evaluated histologically by a retrograde-labeling method and retinal whole mount or sections.
Results: The authors devised an in vivo imaging technique using a conventional retinal camera and visualized RGCs at the single-cell level. In the ischemia reperfusion model, a longitudinal reduction in the number of RGCs was demonstrated in each mouse eye. The number of RGCs and the fluorescence intensity of the nerve fiber decreased considerably during the first week. The percentages of RGCs decreased to 34.2% +/- 7.5%, 24.1% +/- 9.1%, 23.0% +/- 9.3%, and 22.2% +/- 8.4% (mean +/- SD, n = 5) of the percentages before injury at 1, 2, 3, and 4 weeks after injury, respectively (P < 0.001). In this transgenic mouse, 97% of CFP-expressing cells were RGCs and 73% of RGCs expressed CFP.
Conclusions: This in vivo technique allows noninvasive, repeated, and longitudinal evaluation of RGCs for investigation of retinal neurodegenerative diseases and new therapeutic modalities for them.