AIM:To characterize the circadian fluctuation of intraocular pressure(IOP)and ocular perfusion pressure(OPP)at habitual position in newly diagnosed patients with untreated primary open angle glaucoma(POAG)and to test the feasibility of calculating nocturnal peak IOP from the diurnal mean IOP.

METHODS:Nineteen patients(19 eyes)with POAG and eighteen healthy controls(18 eyes)were included and underwent 24-hour monitoring of IOP and blood pressure. At 10:00, 14:00, 18:00 and 22:00 o'clock in the daytime, all the subjects were monitored in sitting position while at 02:00, 05:00 and 07:00 o'clock at night in supine position. For testing the feasibility of calculating nocturnal peak IOP from mean IOP in diurnal supine, all patients still needed to be monitored for IOP in supine position after lying for 5min in the daytime. Measurements were taken in diurnal supine at 2:00, 5:00 and 7:00. OPP was calculated and analyzed. Nocturnal peak IOP was calculated with known formulas and compared with the actual values.

RESULTS:The mean IOP and the fluctuation of IOP of POAG group were higher than those of healthy group in 24-hour habitual position(P<0.05). The mean peak IOP appeared at 05:00 o'clock in POAG patients while at 07:00 o'clock in healthy controls. Both groups had higher mean nocturnal IOP than diurnal(P<0.05). In both groups, the nocturnal mean ocular perfusion pressure(MOPP)was lower than diurnal(P<0.05). However, there was no obvious difference between two groups on MOPP(P>0.05). POAG group had higher fluctuation of MOPP than that of healthy group(P<0.05). Besides, there was no difference between actual peak IOP and values calculated from formulas(P>0.05).

CONCLUSION:The peak IOP of habitual position in patients with POAG and healthy people appears in the morning, and POAG group has higher mean IOP and fluctuation of IOP. Nocturnal OPP is lower than diurnal OPP in both groups, and POAG group has larger fluctuation of MOPP. It might be feasible that we could calculate nocturnal peak IOP from the diurnal mean IOP.