Low nocturnal ocular perfusion pressure as a risk factor for normal tension glaucoma.

Objectives: In the absence of raised intraocular pressure (IOP), haemodynamic parameters have been implicated in the development of normal tension glaucoma (NTG). The purpose of this study is to compare 24-hour IOP and haemodynamic parameters in NTG patients and non-glaucoma patients.

Methods: This is a cross sectional study involving 72 NTG patients from University of Malaya Medical Centre eye clinic glaucoma registry. The non-glaucoma patients were volunteers selected from eye clinic patients. All enrolled patients underwent 24-hour IOP and blood pressure monitoring via 2-hourly IOP and blood pressure (BP) measurements. All readings were taken in the sitting position during the diurnal period and in the supine position during the nocturnal period

Results: Comparison of the haemodynamic parameters, the nocturnal mean systolic BP, nocturnal mean diastolic BP and nocturnal mean arterial pressure (MAP) were significantly lower in the NTG group. The systemic ocular perfusion pressures (OPP), diastolic OPP and mean OPP taken at night were also significantly lower in the NTG group. The differences between the groups were still manifest after controlling for age and presence of hypertension.

Conclusion: Our findings show that the nocturnal supine blood pressure parameters (systolic, diastolic and mean) and OPP were significantly lower in the NTG group compared to normals. This may reflect defective autoregulatory mechanisms in NTG patients.