Increased systemic oxidative stress and impaired antioxidant protection have been shown to associate with primary open-angle glaucoma (POAG), exfoliation syndrome and exfoliative glaucoma. In their study, Tanito et al. evaluated the biological antioxidant potential (BAP; a measure of antioxidative status), diacron reactive oxygen metabolites (dROM; a measure of oxidative status) and sulfhydryl level (SH; a measure of thiol-mediated antioxidative status) in peripheral blood samples of Japanese control subjects (n = 126), POAG patients subdivided into high (n = 117) and low tension (n = 89) groups, and exfoliative syndrome patients with (n = 131) and without (n = 68) glaucoma. They found a significantly lower BAP level in POAG compared to the control group, and a tendency for lower BAP level for all exfoliative eyes. The SH level was lower in their total exfoliation group than in the control and POAG groups, while no difference between the groups was found for dROM levels. After adjustment for the potential confounding effects, they found that glaucoma was significantly associated with lower systemic BAP levels but was unrelated to systemic dROM and SH levels. Based on their large patient population, the authors' main result strongly confirms those of previous similar studies suggesting that in POAG and exfoliation syndrome/ glaucoma the systemic antioxidant capacity is reduced, which may play a role in the development of optic nerve damage. On the other hand, the authors' detailed subgroup comparisons need to be dealt with caution. High and low tension POAG were separated using historical IOP data. Exfoliation group eyes with a history of IOP > 21 mmHg or with glaucomatous disc damage were considered exfoliative glaucoma cases, which does not exclude a combination of exfoliation syndrome and an exfoliation-unrelated glaucoma. Since the IOP values used for patient classification were historical data, and were not based on daytime or 24-hour IOP curves, the results of subgroup comparisons may be biased.