Purpose:
To compare the longitudinal profiles of RGC injury after optic nerve crush and ischemic reperfusion injury with a new technique for in vivo imaging of RGCs.
Methods:
A blue-light confocal scanning laser ophthalmoscope (bCSLO, 460 nM excitation and 490 nm detection) was used to image 10 Thy1-CFP mice aged 3-9 months. RGC degeneration was induced by crushing the optic nerve (n=5) or elevating the intraocular pressure at 115mmHg for 90 minutes (n=5). Corresponding retinal areas before and after optic nerve crush or ischemic reperfusion injury were compared and the fluorescent spots representing Thy1-CFP expressing RGCs were counted manually. The longitudinal profiles of RGC degeneration were modeled with exponential decay equations.
Results:
A significant and progressive loss of Thy1-CFP expressing RGCs was observed at weeks 1, 2, and 3 after the optic nerve crush (18.6±2.3%, 11.3±3.4%, and 8.9±5.3% surviving, respectively; p<0.001; n=5). In contrast, though significant loss of Thy1-CFP expressing RGCs was observed at one week after ischemic challenge (average RGC survival was 47.7%+/-21.1%, p<0.001, n=5), no significant change was detected in any of these mice at weeks 2 and 3 after challenge. In contralateral control eyes, there was no change in Thy1-CFP expressing RGCs. Fitting the experimental data to exponential decay equations, the half-life of Thy1-CFP expression was 2.1 days after optic nerve crush (y = 0.91e-2.28t + 0.09) and 1.2 days after ischemic reperfusion injury (y = 0.53e-4.08t + 0.47) (see Figure).
Conclusions:
The mechanism of the loss of RGCs after optic nerve crush differs from the mechanism of the loss of RGCs after ischemia-reperfusion injury. These results support the use of bCSLO imaging for non-invasive longitudinal analysis of RGC injury responses.
Keywords: imaging/image analysis: non-clinical • ganglion cells • ischemia