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Perfusion pressure

The link between blood flow and glaucoma remains controversial

Roibeard O’hEineachain

Posted: Friday, December 1, 2017

There is a broad accumulation of data from epidemiological studies suggesting that reduced ocular perfusion pressure is associated with an increased risk of glaucoma and glaucoma progression, said Leopold Schmetterer PhD, Singapore Eye Research Institute, Singapore.

However, the degree of association between the two conditions is still in question and complex, he told the 8th World Glaucoma Congress.

Dr Schmetterer noted that ocular perfusion pressure is generally calculated by subtracting intraocular pressure, as a proxy for venous pressure, from brachial arterial blood pressure, as a proxy for ocular arterial blood pressure.

The same type of calculation also provides an estimation of the systolic and diastolic ocular perfusion pressure.

“There are many limitations to the way we calculate ocular perfusion pressure, and generally its relationship to ocular blood flow is relatively unclear,” Dr Schmetterer cautioned.

REDUCED OCULAR PERFUSION PRESSURE AS RISK FACTOR
Most of the prevalence studies regarding glaucoma suggest that low ocular perfusion increases the risk of having the disease.

Those studies include the Baltimore Eye Study, the Blue Mountain Eye study, the Singapore Malay Eye Study and the Los Angeles Latino Eye Study. One exception is the Beijing Eye study, which showed no link between the two conditions.

Regarding incidence, Dr Schmetterer noted that the Barbados Eye Study showed a clear relationship between the nine-year incidence of glaucoma and low ocular perfusion pressure at baseline.

In the Rotterdam Eye study, the relationship was less pronounced and only reached significance among participants receiving antihypertensive medication. In the Thessaloniki Eye study, low diastolic ocular perfusion pressure resulting from antihypertensive treatment was associated with increased cupping and a decreased optic disc rim area, even in eyes without glaucoma.

In the Early Manifest Glaucoma Trial (EMGT), patients with low systolic ocular perfusion pressure (<125 mmHg) had a 1.39- and 1.42-fold higher risk of progression over the entire period of the trial, in a univariate and a multivariate analysis, respectively (p=0.038). Fluctuation of ocular perfusion pressure also appears to influence the risk of progression. In a retrospective study carried out in Korea, a 1.0mmHg increase in ocular perfusion pressure fluctuation was associated with 27.2% greater chance of glaucoma progression.

Dr Schmetterer noted that the data are not unequivocal. A meta-analysis published in the American Journal of Ophthalmology indicates that both high and low blood pressure are associated with increased risk of open-angle glaucoma (Zhao et al, AJO 2014, 158:615-627).

“If you pool together all the studies there is a relatively clear indication that both very low and very high blood pressure or perfusion pressure is associated with the disease,” he added.

Leopold Schmetterer: leopold.schmetterer@meduniwien.ac.at