Your eyes may be your windows to the world, but they also give doctors a glimpse inside, at your health, including diseases and conditions of which you may be unaware.

Signs and symptoms of conditions such as diabetes, high cholesterol, stroke and heart disease, just to name a few, are often visible in, on, or around the eyes long before other symptoms are apparent.

That’s why having regular eye exams is so important. “During a fully dilated eye exam, we’re checking your vision and eye health, and we’re also able to see small changes in the blood vessels and tissue in the back of the eye,” explains ophthalmologist Charles Thompson, MD, with The Eye Clinic. “In fact, the eyes are actually the only place in the body where doctors can directly visualize nerves and blood vessels without an incision, providing us with a clear, unobstructed view.”

Recent advancements such as digital retinal imaging allow eye doctors to more easily detect and monitor changes in the eye that look suspicious. “If we see areas of bleeding, swelling or blockages in the eye, this can be an accurate reflection of changes occurring throughout the entire body,” says Dr. Thompson. “Identifying early signs of certain conditions can lead to earlier, more successful treatment in many cases.”

This is one reason the American Academy of Ophthalmology recommends a complete medical eye examination for healthy adults at least once between age 19 and 29; at least twice between age 30 and 39; and every two to four years between age 40 and 64. “People who have a family history of eye problems should be seen earlier, and anyone who is having eye trouble should see a doctor right away,” says Dr. Thompson. He stresses that you shouldn’t wait until you experience symptoms to see a doctor. “Many conditions are ‘silent,’ and have no noticeable symptoms until the disease is advanced.”

Here are some of the most common symptoms an ophthalmologist could identify during an exam, and what they might reflect about your health:

Arterial plaques. Atherosclerosis is the disease process that causes cholesterol plaque to form in arteries, including the carotid arteries in the neck and the coronary arteries. Bits of cholesterol can break away from these plaques and travel through the bloodstream to the eye, where they lodge in small arteries in the retina, the delicate network of blood vessels and nerve cells at the back of the eye. These minute yellowish blockages can be evidence of severe atherosclerosis.

Optic nerve abnormalities. The optic nerve, which transmits visual information from the retina to the brain, is visible at the rear of the eye. A healthy optic nerve should be pink. If it’s pale, it could be an early manifestation of MS, or evidence of a brain tumor or aneurysm.

Retinal defects. Various medical conditions, most commonly diabetes and high blood pressure, can damage the blood vessels and nerves in the retina. This retinal damage — which can cause blindness — can take several forms, including tiny hemorrhages, leaks of yellowish fluid, and puffy-looking whitish patches known as cotton wool spots.

Skin cancer. There are some signs of skin cancer that can’t be caught during a routine skin scan. Some require a closer look — all the way to the back of your eyes. A retinal nevus is a freckle on the back of the eye, just like you’d have a freckle on your skin. These are fairly common, but if the freckles grows larger, it could be a sign of a melanoma.

Pupil abnormalities. The pupils of healthy people are usually (but not always) symmetrical. They’re usually of the same size, and show the same reaction upon exposure to light. If one pupil is bigger than the other, or if one pupil shrinks less, or more slowly, on exposure to light, there could be an underlying medical problem. Possibilities include stroke, brain, or optic nerve tumor, brain aneurysm and multiple sclerosis.

Droopy eyelid. This condition, called ptosis, can be a sign of aging, but in rare cases, it can be evidence of a brain tumor or a neuromuscular disease known as myasthenia gravis (MG), an autoimmune disorder that weakens muscles throughout the body.

Yellow eyes. Diseases of the liver, including hepatitis and cirrhosis, can turn the white portion of the eyes yellow. The color is caused by the buildup of bilirubin, a compound created by the breakdown of hemoglobin, the oxygen-carrying molecule inside red blood cells.

Bulging eyes. Though prominent eyes may simply be a family trait, eyes that appear to bulge may be evidence of thyroid disease. Abnormal levels of thyroid hormone cause tissues surrounding the eye to swell, making it appear that the eye is bulging.

Dry eyes. When symptoms of dry, burning, irritated eyes occur in combination with a dry mouth, that’s indicative of Sjogren syndrome. Sjogren syndrome, along with joint pain, could be rheumatoid arthritis,

Dr. Thompson says if you notice any of these signs in your own eyes, see your eye doctor right away. “The worst thing you can do is ignore one of these signs, or any other change in your eyes. Your vision – and your health – could depend on a quick response.”