The full title of this talk was: Vascular factors in glaucoma: New challenges (new evidence on vascular factors, perfusion pressure, blood pressure, disc hemmorrhages.)
Link between OPP (Ocular Perfusion Pressure) and OAG
BP-IOP = OPP and there are a number of variations such as systolic, diastolic and mean OPP (mean = 2/3 diastolic - IOP)
So, looking at these perfusion equations, we see that low BP or increased IOP can compromise flow to optic nerve. This is the link between ocular perfusion pressure and open angle glaucomas.
There is variability across populations’ prevalence and incidence of the glaucomas as well as the perfusion pressures. In European “white” populations, there is a more or less constant relationship between % of population with high IOP and the prevalence of glaucoma of approx 7 to 1. This ratio more variable in other populations.
Despite all these variations, there is still a consistent association between low OPP and glaucoma, for example, in Barbados, patients with low OPP have more than 3 fold increased prevalence of OAG. A few studies with inconsistent results such as Rotterdam study with opposite pattern in NTG but they used probable as opposed to confirmed glaucoma. The Bejing study found no clear association between perfusion and glaucoma at all.
The Barbados study followed OPP over 9 years and showed a solid association. They were able to show an increased Relative Risk of glaucoma as perfusion pressure dropped.
Dr Leske also looked at EMGT (Early Manifest Glaucoma Trial) data to see if it showed increased risk of progression with low Systolic Perfusion Pressure. In fact, there was a 1.42 hazard ratio if a patient started the study with low Systolic PP. Furthermore, SPP, SBP, CV disease all risk factors in EMGT patients.
IOP and BP relationships to OAG
There is an Interesting and complex interrelationship between IOP and BP with respect to open angle glaucoma. IOP is a major risk factor but still most people in the population do not have an elevated IOP. BP (systolic) and IOP are positively associated. However, BP/Hypertension and OAG only mixed epidemiological evidence so BP not an established risk factor for glaucoma.
In the LA Latino Study there was no rhyme or reason as to the association with BP. Furthermore, in many studies, it is the LOW blood pressure that is the risk factors and high BP may indeed be protective. Back to EMGT, those with higher Systolic BP at baseline had lower progression of glaucoma, adding further weight to this argument that low BP/perfusion is the greater concern in glaucoma.
in greece, decreased cupping and rim if diastolic BP <90 on antyhypertensive drugs; so are systemic antihypertensives increasing risk of glaucoma? The Rotterdam study also makes us wonder if Calcium channel blocker use increased the risk factor for glaucoma.
Open Angle Glaucoma is multifocal and vascular factors are likely. Interpreting the epidemiological and clinical data, is OPP (Ocular Perfusion Pressure) independent risk factor? OPP could be influenced by low BP alone or high IOP, treatments to lower BP or IOP, vascular status. BP & IOP vary over time and across populations.
What is the role of BP alone, if any , in risk/progression based on brachial artery measurement? Many of our OHT patients also have high BP; will treating their BP, reduce OPP enough to cause glaucoma progression? Furthermore, are there treatments to optimize the OPP?