New evidence illuminates roles of blood pressure and perfusion pressure in glaucoma risk

June 1, 2008

Cross-sectional data from the Los Angeles Latino Eye Study were analyzed to examine associations between blood pressure, perfusion pressure, and the risk of having glaucoma. Results of multivariate logistic regression analyses showed low perfusion pressure, low diastolic blood pressure, and elevated systolic blood pressure were independent risk factors.

Key Points

Washington, DC-Analyses from the Los Angeles Latino Eye Study (LALES) show that low systolic, diastolic, and mean perfusion pressure (PP), low diastolic blood pressure (DBP), and high systolic blood pressure (SBP) all were independently associated with an increased risk of primary open-angle glaucoma (POAG), said Farnaz Memarzadeh, MD, at the annual meeting of the American Glaucoma Society.

"These are all modifiable risk factors, and so it is conceivable that we may be able to reduce the risk of POAG by maintaining BP at a physiologic level on a long-term basis. However, LALES is a cross-sectional study, and the longitudinal relationship between BP, PP, and risk of OAG may be different," said Dr. Memarzadeh, assistant professor of ophthalmology, Doheny Eye Institute, University of Southern California, Los Angeles.

Explaining the background for the analyses, Dr. Memarzadeh noted that although IOP is thought to play a major role in the development and progression of POAG, it also is understood that other factors, especially those affecting the blood supply to the optic nerve head, may play a significant role. Numerous studies have investigated the relationship between POAG, BP, and PP, but data are conflicting.

LALES is a cross-sectional population-based study of adult Latinos in Los Angeles County. Among the 6,130 participants with complete data from a baseline clinical exam and interviewer-administered questionnaire, 287 (4.7%) had POAG. The case subjects with glaucoma were significantly older than the unaffected control subjects (mean age 65 years versus 54.5 years) and had significantly higher IOP (mean 17 mm Hg versus 14 mm Hg). Only 17% of the case subjects were receiving IOP-lowering therapy. About 30% of the subjects had hypertension, and nearly two-thirds of the hypertensive participants were taking BP-lowering medications.

Logistic regression analyses were performed to evaluate the risk of POAG in relation to BP and PP variables. The odds ratios for the BP analyses were adjusted for age, IOP, history of antihypertensive medication use, lifestyle modifications for BP-lowering (e.g., salt restriction), and glaucoma treatment. For the PP analyses, the odds ratios were adjusted for all of those factors except IOP.

Results from analyses

The analyses showed that persons with SBP >160 mm Hg and those with DBP ≤60 mm Hg had an approximate two-fold increased risk of POAG compared with their counterparts in the respective reference groups (SBP 111 to 120 mm Hg; DBP 71 to 80 mm Hg). A trend also was seen for persons with DBP in the higher ranges to have an elevated risk of POAG.

Analyses of the relationships between POAG and PP values showed that individuals with a high systolic PP and low systolic PP had a significantly higher risk of having POAG (2.5- and 2.0-fold increase, respectively). Individuals with a mean PP <50 mm Hg had a four-fold increased risk of having glaucoma compared with the reference group, and as diastolic PP fell below 55 to 60 mm Hg, the risk of having POAG dramatically increased.

Dr. Memarzadeh noted that the associations found in the LALES population between low systolic, diastolic, and mean PPs and low diastolic BP and an increased risk of having POAG are consistent with reports from other cross-sectional studies. Citing the Baltimore Eye Survey, Egna-Neumarkt, Proyecto Ver, the Early Manifest Glaucoma Trial (EMGT), and the Barbados Eye Study, she noted that there is solid evidence that low PPs are associated with an increased risk of having glaucoma, developing glaucoma, and glaucoma progression.

The associations between elevated SBP and PP and glaucoma, however, are more controversial. Although other cross-sectional studies-including Egna-Neumarkt, the Blue Mountains Eye Study, and the Rotterdam Eye Study-showed that elevated BP, hypertension, or both were associated with an increased risk of OAG, recent longitudinal data from the Barbados Eye Study found that hypertension was not a risk factor for incident glaucoma. In the EMGT, hypertension was not a risk factor for glaucoma progression.

Dr. Memarzadeh and her colleagues postulated from their data that both systemic hypertension and hypotension can increase the risk of glaucomatous optic nerve damage by affecting PP, but via different mechanisms.

"In systemic hypertension, chronically elevated BP together with arteriosclerosis can be associated with increased resistance to blood flow at the level of the optic nerve head, which reduces perfusion over the long run. But even on a more short-term basis, it is possible that elevated BP could disrupt autoregulatory mechanisms and lead to reduced perfusion," she explained.

"In systemic hypotension, decreased BP leads to a more direct reduction in PP, and when IOP is elevated, PP is driven down even more."