Twenty-four Hour (Nyctohemeral) Rhythm of Intraocular Pressure and Ocular Perfusion Pressure in Normal-Tension Glaucoma

PURPOSE. To characterize the nyctohemeral rhythm of intraocular pressure (IOP) and ocular perfusion pressure (OPP) in patients with newly diagnosed, untreated normal tension glaucoma (NTG). METHODS. Twenty-seven patients with suspected NTG were prospectively included and underwent 24-hour monitoring of IOP and blood pressure (BP), polysomnography, and nailfold capillaropathy. The nyctohemeral rhythms of IOP, BP, and OPP were modeled with a nonlinear least-squares, dual-harmonic regression procedure, studying the mean value, the acrophase, the nadir and the amplitude of each rhythm. Nonparametric tests were used to study the relationship between the rhythm of IOP and vascular, sleep, and visual field parameters. RESULTS. Five patients were excluded from the analysis after the 24-hour curve of IOP, (IOP > 21 mm Hg during nighttime [n = 1] or daytime [n = 4]). Twenty-two (81%) patients received a diagnosis of NTG (IOP < 22 mm Hg over 24 hours). They exhibited a diurnal acrophase (54.5%), or a nocturnal acrophase (36.4%) of IOP. The remaining patients (9.1%) with NTG had no nyctohemeral rhythm. A significantly higher proportion of patients with capillaropathy and a higher nyctohemeral fluctuation of IOP characterized the IOP group with diurnal acrophase. A rhythm of OPP was found in all patients, (diurnal [58%] or nocturnal [42%]) acrophase) equally distributed between the two groups of IOP. Amplitude of OPP was not significantly associated with the severity or progression of glaucoma. CONCLUSIONS. A nyctohemeral rhythm of IOP exists in most of the patients with NTG, either with a nocturnal acrophase or a diurnal acrophase. The rhythm of OPP did not correlate with the IOP rhythm. (Invest Ophthalmol Vis Sci. 2010; 51: 882-889) DOI:10.1167/iovs.09-3668