Background: The risk of open-angle glaucoma (OAG) may be related to low blood pressure (BP) relative to intraocular pressure (IOP), ie, to low perfusion pressure (PP). Alternatively, systemic hypertension may increase OAG risk.
Objective: To clarify these possible relationships by evaluating hypertension and PP (where PP = BP - IOP) as risk factors for incident OAG in a black population.
Design: Population-based cohort study (85% participation); simple random sample of residents of Barbados, West Indies, aged 40 years and older.
Participants: Two thousand nine hundred eighty-nine black participants at risk; 67 developed OAG after 4 years (2.2% incidence).
Main outcome measure: Adjusted relative risk (RR) of OAG from logistic regression analyses.
Results: The 4-year risk increased markedly with baseline IOP. With an IOP less than or equal to 17 mm Hg, incidence was 0.7%, increasing to 18.3% with IOP greater than 25 mm Hg, for a 25-fold increase in RR. However, OAG developed throughout the IOP range and two thirds of incident cases had baseline IOP less than 25 mm Hg. Baseline hypertension was associated with a halving of the RR of OAG (RR, 0.49; 95% confidence interval [CI], 0.29-0.85); the RR also tended to decrease as systolic BP increased (P =.07). Consistent with these findings, a lower baseline PP increased RR (systolic PP <101 mm Hg, 2.6 [95% CI, 1.3-4.9]; diastolic PP <55 mm Hg, 3.2 [95% CI, 1.6-6.6]; mean PP <42 mm Hg, 3.1 [95% CI, 1.6-6.0]).
Conclusions: As baseline IOP increased, the risk of OAG substantially increased. In contrast, persons with systemic hypertension at baseline had half the RR, suggesting that hypertension does not increase (and may decrease) the 4-year risk of OAG. Lower PP at baseline increased RR approximately 3-fold, a result consistent with the vascular hypothesis of OAG pathogenesis.