A review of ocular perfusion pressure and retinal thickness: A case for the role of systemic hypotension in glaucoma

Background: Ocular perfusion pressure (OPP) is defined as blood pressure (BP) minus intraocular pressure (IOP). Low OPP may result in decreased ocular blood flow (OBF) and oxygen to the optic nerve head (ONH) and retina.Aim: To review the role of systemic hypotension and similar conditions in OPP and its influence on retinal nerve fibre layer (RNFL) thickness and the ganglion cell complex (GCC).Method: A literature search was conducted using the following search terms: ‘systemic hypotension’; ‘glaucoma’; ‘retinal nerve fibre layer’; ‘optic nerve’; ‘ocular blood flow’ and ‘ocular perfusion pressure’.Results: The Los Angeles Eye Study and Barbados Eye Study found that decreased OPP and BP increased the risk of glaucoma development by up to six times. Reduced retinal perfusion with resultant thinning of the RNFL in conditions with a similar mechanism, such as obstructive sleep apnoea syndrome, has indicated the importance of reduced OPP in retinal thickness. In the absence of any study directly showing the effect of systemic hypotension on OPP and retinal thickness, a working hypothesis proposes that reduced BP with or without normal-to-raised IOP will reduce OPP. The reduced OPP and OBF in those with systemic hypotension may result in oxidative stress and hypoxia which may then cause retinal ganglion cell death and the resultant retinal thinning.Conclusion: The increased risk of glaucoma development and progression relating to decreased BP and OPP has been proven to be of importance. Monitoring patients with systemic hypotension and evaluating the macula, ONH RNFL and GCC thickness may alert clinicians to possible glaucomatous changes.