Melatonin Levels in Patients With Primary Open-angle Glaucoma With High or Low Intraocular Pressure

Purpose: To evaluate circulatory melatonin levels by assessing nocturnal urinary excretion of 6-sulfatoxymelatonin (aMT6s) in patients with primary open-angle glaucoma (POAG) and to compare the high-tension group and the low-tension group. Methods: This study included 80 eyes of 41 POAG patients and 87 eyes of 44 control subjects. POAG group was further classified into high-tension group and low-tension group according to the pretreatment intraocular pressure (IOP). The first urine in the morning was collected and aMT6s were measured using a commercial ELISA kit. Urinary aMT6s levels were expressed as ng aMT6s/mg creatinine. Differences in melatonin levels among the control and POAG subgroups were evaluated by generalized estimating equation adjusting age, sex, sleep duration, and intereye correlation. Results: Urinary aMT6s/creatinine ratio did not differ between POAG and control group (P = 0.097). The difference in the aMT6s/creatinine ratio between the 3 groups-high-tension group with baseline IOP >= 21 mm Hg (19.74 +/- 3.12 ng/mg), low-tension glaucoma group with baseline IOP< 21 mm Hg (26.71 +/- 3.47 ng/mg), and control group (30.35 +/- 3.05 ng/mg)-was statistically significant (P = 0.046). Post hoc analysis revealed that the difference between the control and high-tension glaucoma groups was significant (P = 0.014), whereas the difference between the control and low-tension glaucoma groups was not (P = 0.436). Conclusions: This study found low melatonin levels in high-tension glaucoma compared with the control.