Longitudinal profile of retinal ganglion cell damage assessed with blue-light confocal scanning laser ophthalmoscopy after ischaemic reperfusion injury

Aim: 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 ischaemia induced by acute elevation of intraocular pressure. Methods: A blue-light confocal scanning laser ophthalmoscope (bCSLO, 460 nm excitation and 490 nm detection) was used to image Thy1-cyan fluorescent protein (CFP) mice before and weekly for 4 weeks after transiently elevating the intraocular pressure to 115 mm Hg for 45 min (n = 4) or 90 min (n = 5) to induce ischaemic injury. Corresponding retinal areas before and after the intraocular pressure (IOP) elevation, during the period of ischaemic reperfusion, were compared, and the fluorescent spots (Thy-1 expressing RGCs) were counted. The longitudinal profile of CFP- expressing RGCs was modelled with a linear regression equation. The spatial distribution of RGC damage was analysed in the superior, nasal, inferior and temporal quadrants of the retina. Results: No significant change was found at 4 weeks after 45 min of IOP elevation (n = 4, p = 0.465). The average RGC densities before and 4 weeks after IOP elevation were 1660 (SD 242) cells/mm(2) and 1624 (209) cells/mm(2), respectively. However, significant loss of CFP-expressing RGCs was detected at 1 week following 90 min 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 (162) cells/mm(2) and 680 (385) cells/mm(2), respectively. Diffuse loss of fluorescent RGCs was observed in the spatial distribution analysis. Conclusions: The longitudinal profile of Thy-1 expressing RGC fluorescence loss after ischaemic injury is nonprogressive and unrelated to the duration of reperfusion.