• Intraocular pressure
• clinical trial

Glaucoma is a multifactorial disease characterised by loss of retinal ganglion cells that leads to a characteristic optic neuropathy and associated visual-field changes. It is currently the second leading cause of blindness worldwide, with more than 50 million people affected.1 The precise pathogenesis of open-angle glaucoma (OAG) remains to be elucidated. Intraocular pressure (IOP) is a major risk factor for the development and progression of OAG and is currently our only therapeutic target.2 However, in some patients, glaucoma may continue to progress despite statistically significant IOP reduction.3 4 It may be that other factors, such as impaired ocular blood flow, may be contributory. Recent epidemiological data (eg, the Egna-Neumarkt Study and the Barbados Eye Study) suggest that vascular factors are related to both the risk and progression of glaucoma, and several clinical trials have demonstrated the role of vascular factors as part of the multifaceted pathogenesis of OAG.3 5 6 Nevertheless, the significance of these features has yet to be fully understood, and the clinical implications for patient management remain uncertain.5 7

The normal functioning of tissues depends on continuous adequate perfusion. A crucial element is the presence of a sufficient perfusion pressure to meet tissue needs, a process that requires a balance between arterial and venous blood pressure (BP). Ocular perfusion pressure (OPP) is expressed as the difference between the mean arterial BP and the IOP, and is an important determinant of ocular blood flow.5 7 8 It is necessary to distinguish among different BP parameters: systolic, diastolic and mean arterial BP. The mean OPP can be calculated as two-thirds of the mean arterial BP–IOP, where mean arterial pressure=diastolic BP+1/3 (systolic BP–diastolic BP). Likewise, systolic perfusion pressure equals systolic BP–IOP, and diastolic perfusion pressure equals diastolic BP–IOP. The maintenance of OPP depends on …