Diabetes is a disease in which your blood glucose, or blood sugar, levels are too high. Glucose comes from foods you eat. The cells of your body need glucose for energy. A hormone called insulin helps the glucose get into your cells.

With type 1 diabetes, your body doesn't make insulin. With type 2 diabetes, your body doesn't make or use insulin well. Without enough insulin, glucose builds up in your blood and causes high blood sugar levels.

Over time, high blood sugar may damage the blood vessels and lenses in your eyes. This can lead to serious diabetic eye problems which can harm your vision and sometimes cause blindness. Some common diabetes eye problems include:

• Diabetic retinopathy, which is the leading cause of blindness in American adults. It affects blood vessels in the retina (the light-sensitive layer of tissue in the back of your eye). The blood vessels may swell and leak fluid into your eye. If it's not treated, it can cause serious problems such as vision loss and retinal detachment, where the retina is pulled away from its normal position at the back of your eye.
• Diabetic macular edema (DME), which happens when blood vessels in the retina leak fluid into the macula (a part of the retina needed for sharp, central vision). This usually develops in people who already have other signs of diabetic retinopathy.
• Glaucoma, a group of eye diseases that can damage the optic nerve (the bundle of nerves that connects the eye to the brain). Glaucoma from diabetes happens when the blood vessels in the front of your eye are damaged, and new blood vessels grow near the iris (the colored part of your eye). The blood vessels block the space where fluid drains from your eye. This causes fluid to build up and pressure to increase inside your eye.
• Cataract, which happen when the clear lens in the front of your eye becomes cloudy. Cataracts are common as people age. But people with diabetes are more likely to develop cataracts younger and faster than people without diabetes. Researchers think that high glucose levels cause deposits to build up in the lenses of your eyes.

Anyone with diabetes can develop diabetic eye disease. But your risk of developing it is higher if you:

• Have had diabetes for a long time
• Don't have good control over your high blood sugar or high blood pressure
• Are pregnant
• Have high blood cholesterol
• Smoke tobacco

In the early stages, diabetic eye problems usually don't have any symptoms. That's why regular dilated eye exams are so important, even if you think your eyes are healthy.

You should also watch for sudden changes in your vision that could mean an emergency. Call your doctor right away if you notice any of these symptoms:

• Many new spots or dark wavy strings floating in your vision (floaters)
• Flashes of light
• A dark shadow over part of your vision, like a curtain
• Vision loss
• Eye pain or redness

Talk with your doctor if you have these symptoms, even if they come and go:

• Spots or dark wavy strings floating in your vision
• Blurry or wavy vision
• Vision that changes a lot
• Trouble seeing colors

Eye doctors do dilated eye exams to diagnose eye problems. A dilated eye exam uses eye drops to open your pupils wide so your doctor can look for signs of eye problems and treat them before they harm your vision. Your doctor will also test your vision and measure the pressure in your eyes.

Treatment for diabetic eye problems depends on the problem and how serious it is. Some of the treatments include:

• Lasers to stop blood vessels from leaking
• Injections (shots) in the eye to stop new, leaky blood vessels from growing
• Surgery to remove blood and scar tissue or replace a cloudy lens
• Eye drops to lower fluid pressure in the eye

But these treatments aren't cures. Eye problems can come back. That's why your best defense against serious vision loss is to take control of your diabetes and get regular eye exams. It's also important to keep your blood pressure and cholesterol in a healthy range.

NIH: National Institute of Diabetes and Digestive and Kidney Diseases