If you have ever experienced love at first sight, you know that the heart and the eyes share an intimate connection. Unfortunately, the eyes and the heart are also linked in a less romantic way: through high blood pressure.
Hypertension can damage the small blood vessels that supply the retina, the layer of light-sensitive cells at the back of the eye that are essential to vision. Called hypertensive retinopathy, this condition occurs in 2 to 14 percent of people over age 40.
Hypertension is also a risk factor for other diseases of the eye, including retinal vein and retinal artery blockages, retinal emboli (blood clots), diabetic retinopathy, ischemic optic neuropathy (damage of the optic nerve due to reduced blood flow), glaucoma, and age-related macular degeneration.
All of these conditions, including hypertensive retinopathy, can cause headaches, blurry vision, and if left untreated, loss of vision. What’s more, these conditions may foretell other serious, non-eye-related conditions and events such as stroke, heart failure, and death from cardiovascular disease.
Fortunately, detecting hypertension-related eye problems sooner rather than later can help preserve your eyesight.
Damage to the eye
When your blood pressure is high, the increased pressure can cause damage to several structures in your eye: the retina, macula, and optic nerve.
• Damage to the retina. The small blood vessels in the retina are very delicate, and even slightly elevated pressure can cause them to narrow and thicken. As blood-vessel damage worsens, "cotton-wool spots" (small areas of damaged tissue) and hemorrhages (bleeding) begin to appear in the retina.
Cotton-wool spots are the result of reduced blood flow to the retina. Bleeding occurs when blood leaks out of small tears in the blood vessels.
• Damage to the macula. With further damage, the blood vessels lose their structural integrity, allowing fat and other fluids, in addition to blood, leak out. These leaked substances form hard exudates (blister-like areas) around the macula (the central portion of the retina). This produces swelling of the macula that can lead to vision loss.
•Damage to the optic nerve. When blood pressure is extremely high, blood flow to the optic nerve (which carries visual signals to the brain) can become blocked. This blockage causes swelling of the optic nerve that can ultimately result in a permanent loss of vision.
Detecting the damage
Hypertension-induced eye damage—like hypertension itself—often occurs without symptoms, particularly in the early stages. That’s why it’s essential to have a dilated eye exam once a year.
Performed by an ophthalmologist or optometrist, a dilated eye exam can detect damage to the eye before it causes symptoms and at a stage when the changes in the retina are usually reversible.
The specialist will shine a light into your eyes with a device called an ophthalmoscope to look for signs of retinal damage: narrowing of the blood vessels, fluid leaking from the blood vessels, cotton-wool spots or hard exudates in the retina, and swelling of the macula or optic nerve.
In some cases the doctor may also run an imaging test called fluorescein angiography or a similar test called indocyanine green angiography. For these tests, the doctor injects a dye into a vein in your arm.
Once the dye reaches the vessels in your eye, the doctor takes a picture of your retina using a special flash that makes the path of the dye highly visible. These tests show where blood vessels are blocked or leaking.
The most important step in managing hypertension-related eye disease is to gain control of your blood pressure with lifestyle measures and medication. In fact, lowering your blood pressure can reverse some of the damage to the retina, especially when it is in its earliest stages. Better blood pressure control will also help slow progression of the damage, helping to preserve your eyesight.
It’s also important to quit smoking and control high cholesterol and blood glucose levels with lifestyle measures and medication (if necessary), as all of these can worsen the negative effects of hypertension on the eye.
As hypertension-related eye damage progresses, blood pressure control alone may not be enough. Your doctor may recommend injections of medication into the eye or a surgical procedure, such as laser photocoagulation, to slow the damage.
Rarely, very high blood pressure can lead to an eye emergency. When this happens, the patient must be admitted to the hospital, where medication is given intravenously to lower blood pressure and prevent permanent damage to the eye.
If you have high blood pressure and experience a sudden change in your vision, call 911 and your doctor immediately.
The good news
In most instances, hypertension-related eye disease progresses slowly. While this means the condition could go undetected for some time before you notice changes in your vision, it also means that, if you have an annual dilated eye exam, any problems can be detected early and treated before permanent vision changes occur.