Instead of viewing hypertension as beneficial in the fight against glaucoma, it should be identified as a risk factor, an Australian research team suggests.
That’s because, in older patients, any benefit from high blood pressure counteracting high intraocular pressure is lost as damage to blood vessels—a consequence of hypertension—becomes more prevalent, according to a study in the December issue of Investigative Ophthalmology & Visual Science (IOVS).1
The idea that hypertension has protective qualities against IOP elevation was supported by research conducted in the 1990s, which found systemic hypertension to be protective for younger patients, but a risk factor in older patients.2 Those authors proposed that patients in the early stage of hypertension are likely to benefit from improved ocular perfusion pressure and blood flow to the eye.
|Contrary to earlier theories, chronic high blood pressure adds a risk for glaucoma. Photo: James L. Fanelli, OD|
In the recent experimental study in IOVS, researchers compared the effect of normal blood pressure with one-hour (acute) and four-week (chronic) hypertension in lab rats with elevated IOP.
The team found that rats with chronic hypertension did not get the same protection against elevated IOP. The researchers partially associate the effect with a reduced capacity for ocular blood flow to autoregulate in response to IOP elevation in chronic hypertension.
“What this means is that having high blood pressure for a longer time has compromised the eye’s capacity to cope with high eye pressure. It seems that hypertension might damage the blood vessels in the eye so that they can’t compensate for changes in blood flow when eye pressure increases,” says researcher Bang V. Bui, PhD, BSc(optom), of the University of Melbourne.
The authors acknowledged that chronic hypertension in their experiment was limited to four weeks. They speculated that, with longer periods of hypertension and thus more severe vascular damage, the protective effect of high blood pressure might be further reduced.
1. He Z, Vingrys AJ, Armitage JA, et al. Chronic hypertension increases susceptibility to acute IOP challenge in rats. Invest Ophthalmol Vis Sci. 2014;55:7888-95.
2. Tielsch JM, Katz J, Sommer A, et al. Hypertension, perfusion pressure, and primary open-angle glaucoma. A population-based assessment. Arch Ophthalmol. 1995;113:216-21.