Tracking retinal microgliosis in models of retinal ganglion cell damage.

Purpose: To investigate the longitudinal profiles of microgliosis after optic nerve injury induced by optic nerve crush and acute elevation of intraocular pressure (IOP).

Methods: A confocal scanning laser ophthalmoscope was used to image the retinal microglia of the CX3CR1(GFP/+) transgenic mice in vivo at baseline, 3 days and then weekly for 4 weeks after optic nerve crush (n = 3), and after elevating the IOP to 110 mm Hg for 30 (n = 3) or 60 (n = 3) minutes.

Results: After optic nerve crush, the density of microglia increased by 2.43 ± 0.19-fold at week 1 and then gradually declined with 2.04 ± 0.24-, 1.69 ± 0.25-, and 1.29 ± 0.11-fold increases at week 2, 3, and 4, respectively. Microgliosis followed a similar pattern after acute IOP elevation and the increase in microglia was associated with the duration of IOP elevation. There were 1.35 ± 0.17- and 2.03 ± 0.08-fold increases in microglia at week 1, and 1.15 ± 0.11- and 1.11 ± 0.10-fold increases at week 4, after 30 and 60 minutes of acute IOP elevation, respectively. The morphology of microglia changed from ramified to ameboid form in 1 week, and then returned to ramified form in the subsequent weeks. There was a significant negative association between the number of surviving retinal ganglion cells (RGCs) and the extent of microgliosis during the follow-up period (R² = 0.72, P = 0.004).

Conclusions: Longitudinal in vivo imaging of the retinal microglia can provide an effective approach to study microgliosis and its association with RGC degeneration.