High Blood Pressure Must Be Carefully Managed In Glaucoma Patients

MedicalResearch.com Interview with:
Zheng He and Bang V. Bui

Department of Optometry & Vision Sciences
University of Melbourne, Parkville, Australia

Medical Research: What is the background for this study? What are the main findings?

Response: Glaucoma, the second leading cause of blindness in the world, is a condition that occurs when too much pressure builds up inside the eye. This excess pressure injures the optic nerve (the wire that transmits visual information to the brain) resulting in vision loss. Many risk factors for glaucoma are not well understood.

High blood pressure (> 140/90 mmHg) is probably the most common comorbidity in patients presenting to optometry clinics. The overall prevalence of hypertension worldwide is over 26%, and increases dramatically with advancing age. Long-term hypertension leads to remodeling of the heart and blood vessels, promoting the risk of multiple end organ damage.

Whilst chronic hypertension is a well-documented risk factor for stroke, the link between hypertension and glaucoma remains unclear. Previously, it was thought that high blood pressure could counteract high intraocular pressure, which is a clear risk factor for glaucoma. However, this issue may be more complicated than first thought.

The Baltimore Eye Survey compared the prevalence of glaucoma in young and older patients with hypertension. They found that young patients with high blood pressure were at lower risk of glaucoma compared to the entire cohort. This outcome is consistent with the idea that higher blood pressure provides better perfusion pressure to the eye. Paradoxically systemic hypertension in older subjects actually increased the risk of glaucoma. Its seems that longer durations of systemic hypertension impact glaucoma risk negatively. One explanation for this is that any benefit from high blood pressure counteracting high eye pressure is lost as damage to blood vessels — a consequence of hypertension — becomes more dominant.

This hypothesis was tested by comparing the effect of acute (one hour) and chronic (four weeks) hypertension in lab rats with elevated eye pressure. When blood pressure was raised for four weeks, there was less functional protection against eye pressure elevation compared with the one-hour case. This shows that having high blood pressure for a longer time compromises the eye’s capacity to cope with high eye pressure. This impairment was associated with thicker and narrower blood vessels and a reduced capacity for the eye to maintain blood flow at normal levels in response to eye pressure elevation (this process is known as autoregulation). Thus in chronic hypertension, smaller reduction in ocular perfusion pressure can result in blood flow deficiency.

Medical Research: What should clinicians and patients take away from your report?

Response: This new understanding of the consequences of high blood pressure will help clinicians treat patients with glaucoma. It highlights the need for clinicians to not only screen for hypertensive retinopathy in patients with high blood pressure, but also be mindful to integrate blood pressure status and its chronicity into glaucoma assessment along with other risk factors. The Thessaloniki Eye Study has shown that whilst high blood pressure is detrimental, over-zealous treatment of blood pressure can also lead to increased risk of glaucoma. This later finding suggests that the eye in hypertensive individuals is accustomed to higher “ocular perfusion pressures” and that abrupt and excessive reductions in blood pressure does not give the eye time to adjust to the lower perfusion pressure leading to blood flow deficiency.

Medical Research: What recommendations do you have for future research as a result of this study?

Response: Further studies in this area might better inform how to treat patients with hypertension who also develop glaucoma. Specifically, we need to titrate appropriate blood pressure ranges for patients with glaucoma and coexisting high blood pressure. We also need to optimize how gradual hypertensive treatment should be to allow the eye time to acclimatize to the new perfusion pressure.

Citation:

Chronic Hypertension Increases Susceptibility to Acute IOP Challenge in Rats
Zheng He, Algis J. Vingrys, James A. Armitage, Christine T. Nguyen, and Bang V. Bui

IOVS December 2014 55:7888-7895; published ahead of print November 4, 2014,
doi:10.1167/iovs.14-15207

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