Assessment of IOP levels and glaucoma in D2.Tyrp1B6GpnmbB6mice. A. IOP profile of a population of D2 mice (1437 IOPs) between 4 and 20 months of age. B. IOP profile of 88 D2.Tyrp1B6GpnmbB6mice between 6 and 18 months of age. Individual IOP measurements are plotted as circles. The horizontal line indicates 21 mmHg, a value considered to be glaucoma-suspect in people. IOP elevation above 21 mmHg is first observed in D2 mice at around 6 months of age, and peaks at 9–10 months. D2.Tyrp1B6GpnmbB6mice show no significant IOP elevation above 21 mmHg. C. Previously reported frequencies of optic nerve damage in D2 mice are presented showing clear glaucomatous damage. Approximately 70% of D2 eyes have moderate or severe damage by 12 months of age, and 80% by 16–19 months of age. D. In contrast no glaucomatous damage was seen in 18 D2.Tyrp1B6GpnmbB6eyes at 12 months of age, and only 5% (3 of 39) of eyes from 16–19 months of age had obvious disease. A total of 72 eyes were analyzed for all ages. Mild nerves have fewer than 5% damaged axons, moderate (mod) nerves have between 5% and 50% axon damage, and severe nerves have greater than 50% axons damaged. Only moderate and severe nerves are considered to show glaucomatous damage, as mild damage is frequently observed in aging non-glaucomatous strains by 10 to 12 months of age. At 12 months of age, moderate damage is very unusual in non-glaucomatous strains and so we consider this degree of damage a sign of glaucoma. Although moderate damage is not common in non-glaucomatous mice, it does occur in more mice of non-glaucomatous strains by 16 to 18 months. Thus, at these older ages, moderate damage may be caused by an unusual degree of age-related RGC demise or by glaucoma. The single case of severe damage is extremely rare in control mice and may or may not represent glaucoma.