The retina is one of the few places in the body where a doctor can look at live blood vessels, nerves and tissue without cutting a single incision. That is why an eye exam can pick up more than a new glasses prescription.
The American Academy of Ophthalmology says the eyes are "windows to the live action of blood vessels, nerves and connective tissues throughout your body," and three of the conditions it most reliably reveals are high blood pressure, high cholesterol and diabetes.
Some of those clues also point to trouble in the heart and brain. An eye doctor may spot the first hint of an impending stroke, and specific signs on the retina map onto specific systemic diseases.
What high blood pressure looks like on the retina
Chronic hypertension reshapes the small arteries at the back of the eye. Vessels can narrow, kink, nick each other where they cross, and swell. The Academy notes that unusual bends, kinks or bleeding from vessels in the back of the eye can signal high blood pressure, and the retinal picture often shifts before a patient notices any symptoms.
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Clinicians at UMass Memorial Health put it plainly, noting that twisted, kinked or leaking vessels and swollen optic nerves can be a sign of high blood pressure. Because hypertension is often silent, an eye exam is sometimes the first place it is caught.
Cholesterol clues: corneal rings and Hollenhorst plaques
High cholesterol shows up in two distinct ways. A yellow or blue ring around the cornea, called arcus, can be a sign of high cholesterol, particularly in someone younger than 40. The second sign is more urgent. Small, bright, yellow-orange fragments called Hollenhorst plaques can appear inside the retinal arteries.
These are cholesterol emboli that have broken off atherosclerotic plaques in a larger artery, usually the carotid, and lodged in the retina. A StatPearls review published by the National Library of Medicine describes them as "microscopic cholesterol emboli that can be found in the small blood vessels of the retina" and notes that patients with retinal cholesterol plaques had a higher incidence of stroke than people without them, at 8.5 percent versus 0.8 percent in the cohort studied. Finding one on a routine exam is usually a prompt to work up the carotid arteries and cardiovascular risk.
Diabetes and the leaking retina
Diabetic retinopathy is damage to the small vessels in the retina caused by long-standing high blood sugar. In the earliest stage, tiny bulges called microaneurysms form, and vessels can leak yellow fluid or blood.
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The National Eye Institute describes diabetic retinopathy as "an eye condition that can cause vision loss and blindness in people who have diabetes," and its guidance is direct. Anyone with diabetes should have a comprehensive dilated eye exam at least once a year. In some cases, the retinal changes are what first tell a patient that their blood sugar has been out of control.
When to book the exam
For adults with no symptoms and no risk factors, the Academy recommends a baseline eye disease screening at age 40, because early signs of disease and changes in vision often begin at that age. After that, the Comprehensive Adult Medical Eye Evaluation Preferred Practice Pattern suggests an interval of every 2 to 4 years for ages 40 to 54, every 1 to 3 years for ages 55 to 64, and every 1 to 2 years for adults 65 and older.
Anyone with diabetes, high blood pressure, a family history of eye disease or new visual symptoms should not wait for that schedule. And nothing on a retina replaces a conversation with a primary care doctor about blood pressure, cholesterol and blood sugar, but a dilated eye exam can be one more chance to catch a problem early.
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