We administered the PDE5 inhibitor tadalafil orally (10 mg/kg/day) in murine models of two forms of glaucoma - primary open angle glaucoma (POAG; GC-1<sup>-/-</sup> mice) and primary angle-closure glaucoma (PACG; Microbead Occlusion Model) - and measured RGC viability at both the soma and axon level.