Twenty-four-hour pattern of intra-ocular pressure in untreated patients with primary open-angle glaucoma

To investigate and compare the 24-hr intra-ocular pressure (IOP) pattern among different severities of glaucomatous optic neuropathy (GON) together with different subtypes of primary open-angle glaucoma (POAG).

The IOPs of untreated patients with POAG were measured every 2 hrs over a 24-hr period. Subjects were divided into mild, moderate and severe groups according to the glaucoma staging system 2. The two POAG subtypes, normal tension glaucoma (NTG) and hypertension glaucoma (HTG) were classified according to peak IOP values throughout the 24-hr period. The 24-hr IOP curves were obtained based on the average IOP value at each time-point. The mean, peak, trough and fluctuation of IOP together with the diurnal-to-nocturnal IOP change were calculated and compared among different groups.

A total of 160 POAG patients (84 NTG and 76 HTG) were enrolled in the study. Generally, IOP decreased in the diurnal period and increased progressively during the nocturnal period, with peak IOP occurring from 2:00 AM to 10:00 AM. The average IOP values at all time-points were significantly higher in the mild group compared to the moderate and severe groups (p < 0.05). Compared with the NTG subjects, the IOP parameters including mean, peak, trough and fluctuation were significantly higher in the HTG subjects (p < 0.001), and IOP increased more predominantly in the HTG subtype during the nocturnal period.

There was some regularity in the 24-hr IOP pattern in POAG, but different severities of GON and different subtypes might present different characteristics. Other non-IOP factors may lead to pathological IOP fluctuation and could be correlated with GON.