Relationship Between Nocturnal Intraocular Pressure Elevation and Diurnal Intraocular Pressure Level in Normal-Tension Glaucoma Patients.

Purpose: We studied the relationship between nocturnal habitual position IOP elevation and diurnal IOP level in normal-tension glaucoma (NTG) patients.
Methods: A total of 70 young NTG patients with a low diurnal IOP level (mean diurnal seated IOP < 15.0 mm Hg; low IOP group) and 79 age-, axial length-, and disease severity-matched NTG patients with a high diurnal IOP level (mean diurnal seated IOP ≥ 15.0 mm Hg; high IOP group) were recruited prospectively. Intraocular pressure was recorded 11 times over a 24-hour period by a single, well-trained ophthalmology resident using a hand-held tonometer.
Results: The mean habitual position IOP during nighttime (14.2 mm Hg) was significantly higher than that of daytime (12.8 mm Hg) in the low IOP group (P < 0.001), whereas no such difference was found in the high IOP group (16.4 vs. 16.3 mm Hg, P = 0.706). The low IOP group showed an overall nocturnal acrophase in habitual-position IOP, with 11 patients (15.7%) having a diurnal, 30 (42.8%) a nocturnal, and 29 (41.4%) no evident acrophase. By contrast, the high IOP group showed no evident peak in habitual-position IOP, with 28 patients (35.4%) having a diurnal, 12 (15.2%) a nocturnal, and 39 (49.4%) no evident acrophase.
Conclusions: In NTG eyes with a low diurnal IOP, there are significant IOP increases at nighttime in the habitual position, whereas there is no significant nocturnal IOP elevation in NTG eyes with a high diurnal IOP.