HPGDS and open-angle glaucoma: It has been found that POAG patients exhibit low levels of circulating glutathione, suggesting a general impairment of the antioxidative defense [17], while reduced expression of the antioxidant enzymes SOD and glutathione S-transferases was found in the aqueous humor of POAG patients, suggesting that this state could aggravate the balance between both oxygen- and nitrogen-derived free radical production and their detoxification.