Hypertension and Your Eyes

Bradley Anderson, M.D.
St. Cloud Eye Clinic

Systemic hypertension or “high blood pressure” affects more than 50 million Americans. Since hypertension is asymptomatic until late in its course, it remains undiagnosed in roughly half of those who have it. Hypertension is one of the main risk factors involved with atherosclerosis or “hardening of the arteries”, the process by which the arterial circulation becomes less elastic. Other risk factors for atherosclerosis include increasing age, male sex, elevated LDL cholesterol, low HDL cholesterol, smoking, physical inactivity, stress, and family history of early coronary artery disease. Since hypertension contributes to atherosclerosis and atherosclerosis results in hypertension, it is important to screen for high blood pressure and to treat hypertension early in order to prevent irreversible damage to organs throughout the body. Most notably, untreated hypertension and atherosclerosis increases your risk of stroke, congestive heart failure, and renal failure. Proper control of blood pressure has been shown to reduce your risk of these conditions, improving your life expectancy and quality of life. Hypertension cannot be treated, however, unless you screen for high blood pressure; therefore, regular visits to you primary care provider is encouraged. Although this condition is primarily detected and managed by primary care providers, there are many ways that chronic, uncontrolled hypertension can adversely affect your eyes.

Hypertension is defined as a minimum diastolic pressure of 90 mm Hg or a minimum systolic pressure of 140 mm Hg. Generally, the diastolic blood pressure is considered twice as important as the systolic blood pressure. A blood pressure measurement is an estimate of the amount of pressure in the arterial vessels at the level of the heart, usually measured in the arm. Imagine a person with a blood pressure of “140/90” with a tube running directly from their brachial artery (the main artery in their arm) to a column of liquid mercury. During the contraction phase of the heart (systole) the column of mercury would be 140 millimeters higher than the heart; during the relaxed phase of the heart (diastole) the column of mercury would be 90 millimeters higher than the heart. Therefore, the arterial vessels are constantly under pressure, even under normal circumstances. This pressure is created by the muscles and elastic fibers in the arteries themselves. During the systolic phase, the heart contracts and forces a large amount of blood into the body’s arteries. These arteries stretch to accommodate the increased volume of blood. During the diastolic phase, the heart relaxes and the stretchy elastic fibers in the blood vessels contract and return to their natural shape, much in the same way that an elastic waistband will return to its original diameter. These elastic fibers along with muscles in the arterial walls slowly and steadily squeeze the blood out of the arteries into the tissues that need oxygen and nutrients through tiny capillary vessels. If our vessels were not stretchy, they would function like a copper pipe and our systolic blood pressure would be very high, destroying the delicate capillary vessels throughout the body resulting in massive bleeding. Furthermore, if our vessels were not stretchy, our diastolic blood pressure would be zero. Since diastole is the longer of the two phases when the blood is slowly squeezed into the tissue, a sustained diastolic blood pressure of zero would be fatal since the body’s tissues would not get enough oxygen or nutrients.

Hypertension can damage the eyes directly or indirectly through atherosclerosis. Through atherosclerosis, hypertension can indirectly damage nerve tissue as well. When chronic hypertension causes a loss of arterial elasticity, the duration of perfusion during the “diastolic squeeze”, reviewed above, can cause ischemic damage to the nerve tissue in a process referred to as a “microvascular infarct”. Usually occurring during periods of rest, the blood pressure temporarily lowers resulting in a drop in the diastolic blood pressure (the lower number). A “microvascular infarct” occurs when the elastic artery cannot squeeze long enough to deliver blood through the capillaries throughout the whole period of time between heart beats. As a result, the nerve tissue dies, becomes edematous, and hemorrhages. Examples of this type of ischemic nerve damage would include an ischemic stroke with visual field defects, optic neuropathy (see photo) causing vision loss, and cranial nerve palsies creating double vision from ocular motility dysfunction.

When the systolic blood pressure becomes too high, hypertension damages tissue directly. The elevated systolic blood pressure causes tiny capillary vessels to burst resulting in hemorrhages. If these hemorrhages are small, they show up in the retina as tiny, asymptomatic dot hemorrhages. If the hemorrhages are large, they can irreversibly damage the retina, optic nerve, or brain. Furthermore, high arteriole blood pressure can block the flow of venous blood where a retinal artery and vein crosses, called a branch or central retinal vein occlusion (see photos). This results in a backup of venous blood that swells the retina, interfering with vision. Furthermore, the swollen tissue becomes ischemic, which causes a release of hormones that can cause damaging new vessels to grow. These vessels can lead to neovascular glaucoma, preretinal and vitreous hemorrhages, epiretinal membrane formation, and tractional retinal detachment. Chronically elevated blood pressure can cause the arteries to stretch, resulting in arterial macroaneurysms, which can leak fluid and damage the central vision as well.

The coexistence of hypertension and diabetes mellitus may result in an exacerbation of the diabetic retinopathy. There is even some evidence that suggests that open angle glaucoma, to most common type of glaucoma, has an association with hypertension. Hypertension may cause symptomatic vision loss, but early ocular damage is often asymptomatic, therefore, regular eye exams are recommended for people with hypertension.

The good news is that most of these adverse effects from hypertension are preventable through your primary care provider. Having your blood pressure checked regularly outside of the doctor’s office is also a useful tool for early diagnosis. Together with you, your primary care doctor, and your ophthalmologist, vision loss from hypertension is often preventable.