We tend to think of eye exams as a way to improve or protect our vision. And that’s true. But there’s more to it than that.

“What many people don’t understand is the eye can reveal diseases that are not necessarily related to visual problems,” says Jeff Stovall, a Peachtree Corners optometrist.

Those conditions can include diabetes, high blood pressure and even arthritis or multiple sclerosis.

A comprehensive eye exam can point to these health issues.

Recent research suggests that changes in the retina can actually be predictors of heart disease.

The eye can reveal abnormalities that might indicate a stroke, high blood pressure or even heart failure.

In fact, the retina may detect certain cardiac problems not obvious to the patient. That’s because the changes include narrowing or ballooning of blood vessels and swelling of the base of the optic nerve, according to a report from Harvard Health.

Advancements such as digital retinal imaging allow an eye doctor to find and monitor the blood flow to the retina via the dilated eye exam. An evaluation is done by an optometrist (whose field is testing and correcting vision) or an ophthalmologist (a physician who specializes in all aspects of eye health).

A patient who has a blood flow abnormality may then be directed to a primary care doctor, an internal medicine specialist or a cardiologist for further tests.

Diabetes is another problem. More than 29 million Americans have diabetes, but 1 in 4 don’t know they have it, the CDC says.

For some of those people, an eye exam may reveal the need for further diabetic tests.

“Yes, this happens,” says Dr. Purnima Patel, a clinical spokeswoman for the American Academy of Ophthalmology. She is also an assistant professor of ophthalmology at Emory University School of Medicine in Atlanta.

Professional eye doctors can “see damage to a patient’s retina that is consistent with diabetic damage,” says Patel.

“In such cases where the patient has not been diagnosed with diabetes, we recommend a patient be evaluated by their primary care physician for diabetes,” she says.

The eye exam may be the first time people are aware of diabetes, let alone serious problems with the retina, such as diabetic retinopathy, which is a general term for all disorders of the retina caused by diabetes.

Diabetes is the leading cause of new cases of blindness in adults, says the CDC.

Data from the American Association for the Blind’s Community Survey state that more than 258,000 Georgians have reported serious difficulty seeing even when wearing glasses. (This number includes those who are already blind.)

Perhaps surprisingly to many people, the eyes can be affected by arthritis.

“A diagnosis of arthritis would not necessarily be made with an eye exam alone,” says Patel. “However, some autoimmune diseases that cause arthritis, such as rheumatoid arthritis or lupus, may also have associated eye findings, which can help make a diagnosis.”

Patel also suggests that these patients may have “eye problems including dry eyes, itching, burning, redness, light sensitivity, or even decreased vision or loss of vision.”

Multiple sclerosis has an entirely different way of affecting the eye. Dr. Sanjay Gupta, CNN’s chief medical correspondent, explains that the optic nerve, which is behind the eye, is actually part of the brain. “One early warning sign for MS might be visual problems originating in the optic nerve, said Gupta in a 2008 interview.

Stovall, a doctor of optometry, says newer digital instruments “allow us to demonstrate the importance of annual eye exams.”

“What is especially critical for us and for our patients to understand is most of the things we can find early on are not noticed visually” by the patient, he says.

Stovall’s message: “Even if you believe your eyesight is just fine, it is still necessary to make an annual eye exam appointment.”

People with a history of good vision can become complacent about it. Many never feel the need to get an eye exam until they start experiencing blurred vision, Stovall says.

That’s a big problem, he adds.

“Most of the serious eye diseases like glaucoma or macular degeneration will cause visual damage” before the patient ever notices anything, he says. And by the time the problem becomes obvious, it’s more difficult to treat.

The dilation test

The comprehensive dilated eye exam is a valuable part of an eye check-up, especially for older patients and those in certain high-risk groups.

The pupils of the eyes are something like windows, and looking through them can reveal what goes on deep inside. But getting a thorough look is not easy under most circumstances. As a natural safeguard, these “windows” tend to close (contract) when light shines into them.

In the controlled, protected environment of an eye doctor’s office, the pupils can be artificially dilated using special eyedrops. Once the drops take effect and the patient’s pupils are widened, the eye doctor can use a special magnifying lens to peer deep into the backs of the eyes, studying tissues that would not normally be visible.

(This artificial dilation wears off after a few hours, but patients who leave the doctor’s office may need to wear protective darkened lenses in the meantime.)

As noted, the comprehensive dilated eye exam is recommended for patients in certain categories. For that reason, it may not be part of a standard eye exam for new glasses or contact lenses. It’s a good idea to ask an eye care professional about what’s included, and to discuss whether you need the dilation test.

Medicare does not cover routine eye exams (sometimes called “eye refractions”) for eyeglasses or contact lenses. However, Medicare Part B (medical insurance) covers some preventive and diagnostic eye exams. Once again, ask your eye doctor or a Medicare consultant.

The population of American adults with visual impairment and age-related eye diseases is expected to double in the next 30 years, based on the rapid aging of the nation’s population, the CDC says. (With longer life spans, medical conditions that develop with age are more common.)

And here’s an ominous fact: Diabetes, as well as other chronic diseases, will contribute to an increase in the number of Americans who lose their vision.

Stovall says his business is to keep that number as low as possible. “The goal of every routine eye exam is to prevent blindness,” he reminds his patients.

For aging patients, check-ups for macular degeneration, diabetic retinopathy, glaucoma, and cataracts should be routine, and a professional eye examination should be done annually.

But if other diseases can be found early and treated — so much the better.

Judi Kanne, a registered nurse and freelance writer, combines her nursing and journalism backgrounds to write about public health. She lives in Atlanta.