GFAP and ocular hypertension: Expression of GFAP, an intermediate filament protein that is a marker of macroglial reactivity, was induced and upregulated in Müller glia and astrocytes, as early as 2 weeks after ocular hypertension (Fig. 5A) and remained upregulated in the retina for 8 weeks and was coincident with loss of RGCs as evidenced by RBPMS staining in the GCL layer (Fig. 5B).