Glaucoma is characterized by optic nerve damage which results in vision loss, and elevated eye pressure (intraocular pressure) is the primary risk factor. There is growing evidence that other factors may predispose a person to glaucoma damage, including circulation to the eye and optic nerve. These “non-traditional” risk factors include low blood pressure or perfusion pressure and other vascular factors.
Traditional Risk Factors
Traditional risk factors for glaucoma include elevated eye pressure, family history, age, and ethnicity. There is clear evidence that the risk of glaucoma increases with higher eye pressure.
We also know that the risk of glaucoma increases with advancing age, a family history of glaucoma, and in individuals of African, Asian, or Hispanic descent.
Of these risk factors, the only one your doctor can treat is eye pressure.
High eye pressure alone does not cause glaucoma. Most people with elevated eye pressure do not have and may never develop glaucoma. In addition, various population studies indicate that as many as 40% of those who develop glaucoma have eye pressures that are in the normal range.
Even in patients who have glaucoma with elevated eye pressure, their eye pressure is within the normal range approximately one-third of the time. Clearly, while eye pressure is important in glaucoma, it does not explain why glaucoma develops in all patients.
Other Risk Factors for Glaucoma
Therefore, we look to other risk factors for glaucoma. Most important among these appear related to blood flow to the eye.
Evidence suggests that ocular perfusion pressure is a strong risk factor for glaucoma. Ocular perfusion pressure is the relationship between the eye pressure and the blood pressure.
If the blood pressure is low, especially if the eye pressure is elevated, blood has difficulty getting into the eye to supply oxygen and important nutrients, and to remove waste products.
However, even in individuals with normal eye pressure, their blood pressure may be low enough naturally, or as a result of treatment for their high blood pressure, to deprive the eye of adequate blood flow.
Normally, our bodies adapt to changes in blood pressure, body position, or other changes in order to maintain constant circulation to important areas such as our brain or our eyes. For some individuals, their bodies may lack the ability to adjust the circulation appropriately, so the tissue may not be properly nourished and may suffer damage over time.
What Can We Do Today?
Low ocular perfusion pressure may be improved by lowering eye pressure and/or by increasing blood pressure. While there is strong evidence to support the treatment of glaucoma by lowering eye pressure, there is not enough data to support increasing blood pressure in all glaucoma patients. In fact, increasing the blood pressure could have detrimental effects in other parts of the body.
Monitoring blood pressure and calculating the ocular perfusion pressure can still be helpful, especially in patients who are getting worse despite adequately controlled eye pressure. If it appears that the perfusion pressure to the eye is low, it is important to understand and discuss with your doctor how this may influence your risk and treatment for glaucoma.
Article by Louis B. Cantor, MD.
First posted on January 1, 2015; Last reviewed on April 18, 2022.
Louis B. Cantor, MD
Dr. Cantor is the Jay C. and Lucile L. Kahn Professor of Glaucoma Research and Education and Director of the Glaucoma Service at the Eugene and Marilyn Glick Eye Institute, Indiana University School of Medicine, Department of Ophthalmology, in Indianapolis, Indiana.