Decreased nitric oxide production in primary open-angle glaucoma

Raised intraocular pressure (IOP) is the major risk factor responsible for optic nerve damage in primary open-angle glaucoma (POAG). The trabecularmeshwork acts as a valve in aqueous outflow and relaxes with nitric oxide (NO) agonists. Since NO is synthesized by endothelium and smooth muscle elsewhere in the body, this study investigated the NO levels in the aqueous humor of patients with POAG compared with cataract patients.

Aqueous humor samples were taken by paracentesis from 16 consecutive patients with POAG (9 male and 7 female; mean age 69.0+/-3.4 yrs) and 14 age and sex-matched controls with cataract (8 male and 6 female; mean age 66.7+/-4.1 yrs) during elective surgery. As an indicator for NO, aqueous total nitrite levels (end - product of NO) were measured by Greiss reaction. The Mann-Whitney U test was used for statistical analysis and P <0.05 was considered significant.

The mean age and sex in two groups were comparable. The mean aqueous humor NO levels were significantly (P = 0.001) lower in patients with glaucoma (72.72+/-11.21 micromol/L) than in patients with cataract and no glaucoma (86.92+/-11.23 micromol/L).

Decreased NO production in patients with POAG indicates that NO-producing cells may be lost as the disease progresses. The control of NO levels in the eye might be a therapeutic target in glaucoma.