The Connection Between Blood Pressure and Glaucoma

The Connection Between Blood Pressure and Glaucoma

August 01, 2022

Blood pressure and eye pressure vary independently.  Controlling blood pressure does not mean IOP is controlled. But studies have shown that patients with high blood pressure have an increased risk for glaucoma. Very high blood pressure is not good for glaucoma.

Moderate to very low blood pressure is also a problem because it is important for the optic nerve to receive sufficient blood flow. Evidence suggests that low ocular perfusion pressure is a strong risk factor for glaucoma.

Ocular perfusion pressure is a complex variable that can be considered as the difference between the blood pressure and the eye pressure. If the blood pressure is low and the eye pressure is elevated, blood has difficulty getting into the eye to supply oxygen and important nutrients.

Patients who are taking medication for high blood pressure may actually have their blood pressures dropping to very low levels during the hours they are sleeping. This reduces the amount of blood flow to the eye and optic nerve and may compromise the optic nerve.

The role of blood flow in optic nerve damage is the subject of ongoing study. We now understand that in some forms of glaucoma, there is a strong link between glaucoma and reduced blood flow to the optic nerve.

Although intraocular pressure (IOP) remains an important risk factor for glaucoma, it is clear that other factors can also influence disease development and progression.

More recently, the role that blood pressure (BP) has in the genesis of glaucoma has attracted attention, as it represents a clinically modifiable risk factor and thus provides the potential for new treatment strategies beyond IOP reduction.

The interplay between blood pressure and IOP determines the ocular perfusion pressure (OPP), which regulates blood flow to the optic nerve.

If OPP is a more important determinant of ganglion cell injury than IOP, then hypotension should exacerbate the detrimental effects of IOP elevation, whereas hypertension should provide protection against IOP elevation.

Epidemiological evidence provides some conflicting outcomes of the role of systemic hypertension in the development and progression of glaucoma. The most recent study showed that patients at both extremes of the blood pressure spectrum show an increased prevalence of glaucoma.

Those with low blood pressure would have low OPP and thus reduced blood flow; however, that people with hypertension also show increased risk is more difficult to reconcile.

This finding may reflect an inherent blood flow dysregulation secondary to chronic hypertension that would render retinal blood flow less able to resist changes in ocular perfusion pressure.

While not a systemic disease itself, glaucoma is widely understood to have systemic risk factors. Much of the relationship between glaucoma and the human system has to do with the vasculature of the optic nerve itself.

The 1 million or so ganglion cells that converge to make up the optic nerve are similar to other cells in that they must do two things to survive: eat and breathe. While that is an oversimplification of the two processes, it is essentially accurate.

The cells of the optic nerve depend on the circulatory system for respiration and supply of glucose to make adenosine triphosphate (ATP) and have energy. So, by definition, anything that negatively affects the vascular system has the potential to negatively affect the optic nerves.

Risk Factors

Diabetes mellitus, for example, has long been proposed as a risk factor of the development of openangle glaucoma. The evidence for this may be more compelling than ever before.

With that said, the relationship between blood pressure and glaucoma has been studied for quite some time. Specifically, low blood pressure has been implicated as having a role in the development of open-angle glaucoma, especially in so-called normal tension glaucoma.

With the recent publication of new blood pressure guidelines set forth by the American College of Cardiology and the American Heart Association, it is timely to analyze the relationship between blood pressure and glaucoma and examine the role of optometrists.

Supporting Research

In a 2018 study published in the American Journal of Hypertension, the presence of glaucoma was determined to have a nonlinear relationship with systemic blood pressure. The relationship between the two followed a U-shaped curve, according to the study’s investigators.

This means that the incidence of glaucoma increased in those participants with low and high blood pressure. The study included 4,137 participants from the 2005 to 2008 National Health and Nutrition Examination Surveys (NHANES), all age 40 or older.

The overall prevalence of glaucoma in the study sample was 1.2 percent. Systolic and diastolic blood pressure, separately, were metrics to determine the relationship between these two chronic diseases.

For participants who were not taking antihypertensive medications, the incidence of glaucoma went up with both high systolic blood pressure (greater than or equal to 161 mm Hg) and low systolic blood pressure (less than or equal to 110 mm Hg).

Similarly, the incidence of glaucoma went up with respect to high and low diastolic blood pressure (greater than or equal to 91 mmHg or less than or equal to 60 mmHg, respectively).

The prevalence of glaucoma among study participants was lowest in those with systolic blood pressure between 11 mm Hg and 120 mm Hg and diastolic blood pressure between 81 mm Hg and 90 mm Hg.

This study suggests a sort of “Goldilocks scenario” of blood pressure is preferred with respect to glaucoma, wherein an optimum range exists.

Blood pressure that is too low—naturally or from the overtreatment of hypertension—may lead to decreased ocular perfusion pressure and result in ischemia to the optic nerve. This factor may be especially significant within the arena of normal tension glaucoma.

On the other hand, systemic hypertension, while perhaps not damaging in the short term, often leads to arteriosclerosis, which may decrease perfusion to the optic nerve.

Controversial Link

The relationship between systemic hypertension and glaucoma has traditionally been one of controversy. In fact, the 2008 Barbados Eye Studies showed that systemic hypertension may have an association with a decreased risk for glaucoma.

However, newer research published in 2014 suggests the contrary, with systemic hypertension implicated as having a role in the development of ocular hypertension.

Putting Into Practice

So, with contemporary science suggesting that a range of blood pressure that is not too high and not too low is best for the patient, the question then arises of what eyecare practitioners can do with this information.

Incorporating patient blood pressure measurement into a glaucoma evaluation—if optometrists are not already doing so—is a noninvasive and quick way of determining the presence or absence of a separate risk factor for the development of the disease.

It is incorrect to assume that a patient’s blood pressure is “controlled” simply because he is taking an oral antihypertensive medication. In fact, oral antihypertensive medication use is a common cause of hypotension.  

In addition to the fact that suboptimal blood pressure can contribute to glaucoma, nonselective beta blockers—such as timolol (Timoptic, Betimol; Alcon)— are known to have systemic hypotension and bradycardia in their drug side effect profiles.

Keeping check on metrics such as systemic blood pressure helps optometrists treating glaucoma patients in monitoring patient safety in addition to keeping an eye on potential lurking variables.