By Charlotte Hilton Andersen
January 22, 2014

Take your eyes off that screen for a second: A new study reveals that 70 percent of American adults experience eye strain caused by digital devices. And even if you don't have vision problems, the American Academy of Ophthalmology recommends getting an eye check-up at least once in your 20s and twice in your 30s. Since eyes are affected by many diseases (and are easy to examine), it's easy to diagnose problems throughout your body simply by peering into your peepers, says Brian Francis, M.D., an ophthalmologist at the Doheny Eye Center at Orange Coast Memorial Medical Center. Your eyes might be trying to clue you in on these 10 surprising health conditions.

1. Your Mental Health

It's been known for nearly a century that people with mental illnesses like schizophrenia and bipolar disorder usually have different eye tracking patterns. (Schizophrenic patients, for example, tend to have a hard time keeping eyes focused on slow-moving objects.) But it's only recently that doctors have been able to map those movements and use them to diagnose the notoriously tricky illnesses. Technology previously used to diagnose glaucoma is now also being used to map out visual inconsistencies that identify mental illness, Francis says.

2. If You Have a Brain Tumor

Brain tumors manifest in many different ways. Some symptoms, like headaches and dizziness, you'd expect. But other symptoms you'd never find, unless you looked in your eyes, Francis says. He explains that during a normal eye exam, your doctor will check for blurry vision, improper pupil dilation (one eye dilating more than the other or remaining fixed), and optic nerve color. If your doc suspects anything amiss, you'll likely get a referral to a neurologist for a follow-up.

3. If You Have an Aneurysm

A brain aneurysm occurs when a blood vessel in your brain weakens, causing one part to bulge out. If the vessel breaks, it can cause death very quickly. Often aneurysms go unnoticed until someone is in grave danger, which is why it's great that some of early symptoms can be caught during a routine eye exam. Francis says to tell your eye doctor if you're experiencing blurry vision, eye pain, headaches, or loss of vision. The doc will also check you for drooping eyelids (a sign that a blood vessel may have ruptured or is leaking), increased pressure in your eye, bleeding in the retina, and swelling of your optic nerve. Crossed eyes can be another sign of bleeding in the brain, possibly from an aneurysm or even a stroke.

4. Your Risk for Diabetes

Nearly 10 percent of Americans have diabetes, with many more at risk for the illness. Unchecked, it can cause a host of problems ranging from mild (dizziness or numbness) to severe (limb amputation and even death). To look for evidence of diabetes, your doctor will check for retinal vascular changes and blood vessels hemorrhages in your eyes, Francis says.

5. If That Eye Tic Is Actually Multiple Sclerosis

While most eye tics are benign, they can also be an early indicator of neurological diseases like multiple sclerosis and Parkinson's, so be sure to mention those symptoms to your doctor, says Benjamin Ticho, M.D., a board certified ophthalmologist and a partner at The Eye Specialists Center in Chicago. Your eye doctor can help with early diagnoses by checking for anomalies in your retina and optic nerve.

6. Whether or Not You Have High Blood Pressure

High blood pressure, defined as anything over 120/80, is a known risk factor for heart disease, diabetes, metabolic syndrome, and other illnesses, including blindness. Arteries and veins in the back of the eye can be a predictor of heart disease in women and to a lesser extent men, Noel Bairey Merz, M.D., director of the Women's Heart Center at Cedars Sinai Heart Institute in Los Angeles, said in an interview with ABC News. "The idea is that all of these arteries swim in the same swimming pool and are exposed to the same cholesterol level, sugar level, blood pressure, nutrients or lack thereof, exercise, and smoking."

7. Your Blood Glucose Levels

One surprising cause of those annoying eye twitches is hypoglycemia, or abnormally low blood sugar levels, Ticho says, which can also cause shakiness, sweating, blurry vision, and even seizures. So even it feels like just a minor annoyance, mention the tic to your eye doctor so he can figure out if you really have the condition, which is linked to diabetes as well as metabolic problems and diseases of the liver, kidneys, and pancreas.

8. If You Have Vitamin A Deficiency

Vitamin A deficiency is rare in people with a well-balanced diet. However, if you're not getting enough fruits and veggies (it's found in foods like sweet potatoes, greens, cantaloupe, and carrots), you may develop night blindness and vision loss. Your eye doc will check the surface of your eye for damage, Francis says, and be sure to tell him if you're having any trouble seeing at night.

9. Whether or Not You Have Melanoma

Did you know you can get freckles in your eyes? [Tweet this fact!] And just like you can get freckles and melanoma on your skin, you can also get skin cancer inside your peepers. If you see a constant speck in your eye, ask your doctor to check it out. During a routine exam, he'll also check your eye color and pattern to make sure everything looks normal.

10. If There's Dangerous Pressure Building Up in Your Brain

Idiopathic intracranial hypertension-increased pressure around the brain-is relatively rare, but doctors are seeing more of it, Francis says. The condition is most common in overweight young women. And while the primary symptom is headache, it can also cause blurry or double vision, and can lead to vision loss if not corrected. Your doctor will check your optic nerve for "buckling" and other signs of increased pressure.