D2-Gpnmb+ mice do not develop glaucoma. A-C. H&E stained sections of D2-Gpnmb+ mice at 4.5 mo (A), 12 mo (B) and 18 mo (C) showing a normal nerve fiber layer (arrows) and no evidence of optic nerve cupping. D. H&E section of a 12 months old D2 mouse with severe glaucoma, showing optic nerve cupping (asterisk) and loss of nerve fiber layer (arrows). E-G. PPD staining of the retro-orbital optic nerve from a 4.5 mos (E), 12 mos (F), 18 mos (G) D2-Gpnmb+ mice. These nerves are healthy with only rare degenerating axons, as is typical for nerves of non-glaucomatous mouse strains. H. Severe glaucoma in a 12 mos D2 eye. Healthy axons have clear axoplasm, surrounded by darkly stained myelin (arrow). The sick or dying axons stain grey/black (arrowhead). (I) Frequency of glaucomatous optic nerve damage in D2-Gpnmb+ mice, using the 3 point grading system (see Methods). No D2-Gpnmb+ mice show severe glaucoma, and only 3 eyes show moderate damage. Importantly, these moderately affected nerves only just enter this grade (all had less than 10% axon loss), and were not as severely degenerated as the typical D2 moderate nerve.