Purpose: To longitudinally investigate retinal ganglion cell (RGC) expression of Thy-1, a cell-surface glycoprotein specifically expressed in RGCs, with a blue-light confocal scanning laser ophthalmoscope, following retinal ischemia induced by acute elevation of intraocular pressure.
Methods: A blue-light confocal scanning laser ophthalmoscope (bCSLO, 460nm excitation and 490nm detection) was used to image Thy1-CFP mice before and weekly for 4 weeks after transiently elevating the intraocular pressure to 115 mmHg for 45 minutes (n=4) or 90 minutes (n=5) to induce ischemic injury. Corresponding retinal areas before and after the IOP elevation, during the period of ischemic reperfusion, were compared and the fluorescent spots (Thy-1 expressing RGCs) were counted. The longitudinal profile of CFP-expressing RGCs was modeled with a linear regression equation. The spatial distribution of RGC damage was analyzed in the superior, nasal, inferior and temporal quadrants of the retina.
Results: No significant change was found at 4 weeks after 45 minutes of IOP elevation (n=4, p=0.465). The average RGC densities before and 4 weeks after IOP elevation were 1660+/-242cells/mm2 and 1624+/-209cells/mm2, respectively. However, significant loss of CFP-expressing RGCs was detected at 1 week following 90 minutes of IOP elevation (n=5, p<0.001). After this initial RGC loss, no significant change was detected subsequently. The proportion of RGC fluorescence remaining was variable and ranged from 14.5% to 79.5% at 4 weeks after the IOP elevation. The average RGC densities before and 4 weeks after IOP elevation were 1443+/-162cells/mm2 and 680+/-385cells/mm2, respectively. Diffuse loss of fluorescent RGCs were observed in the spatial distribution analysis.
Conclusions: The longitudinal profile of Thy-1 expressing RGC fluorescence loss after ischemic injury is non-progressive and unrelated to the duration of reperfusion.