The link between diabetes and eye health might not seem obvious at first. But diabetes is a condition that damages blood vessels, including those that feed the eyes and support vision. In fact, the connection is so strong that about one in three adults with diabetes will develop diabetic retinopathy — diabetes-related damage to the retina that leads to vision loss, according to the Centers for Disease Control and Prevention. Yet in its earliest stage, the disease often has no symptoms, so it's important to be proactive with diabetes care and eye health to help prevent or slow this complication.
The Effects of Diabetes on the Retina
The retina is a thin piece of tissue lining the back of the eye. Light comes through the lens of the eye and focuses images onto this tissue. The center of the retina, the macula, is responsible for detailed images. Diabetic retinopathy occurs when diabetes affects small blood vessels throughout the body, including those that supply blood to the eyes.
“In the earliest stages of diabetic retinopathy, changes are seen in the blood vessels in the eye,” says Paul Bernstein, MD, PhD, an ophthalmologist and professor of ophthalmology at the John A. Moran Eye Center at the University of Utah in Salt Lake City. Blood vessels become weak, leak, or close up. Changes in blood flow can lead to swelling and trigger the growth of new blood vessels. Scarring, new growth, and bleeding in turn lead to tearing of the retina and swelling of the macula, a condition called macular edema.
There are two forms of diabetic retinopathy. In the early-stage form called non-proliferative diabetic retinopathy, the blood vessels begin to weaken and bleed, but people usually have few symptoms.
The second form is called proliferative diabetic retinopathy, which is the later stage of the disease. New blood vessels start to grow to accommodate the changing blood flow. Without adequate blood flow, the retina may tear or change shape, causing vision loss or blurred vision.
Risk factors for developing diabetic retinopathy include having uncontrolled high blood sugar, having a family member with diabetic retinopathy, having had diabetes for a long time, having high blood pressure and high cholesterol levels, being pregnant, and being Hispanic, Native American, or African American.
Controlling blood sugar helps prevent retinopathy. People with diabetes who are able to keep their A1C level — which measures your average blood sugar level over two to three months — under 7 have fewer retinal complications than those with less effective blood sugar control, according to research published in the journal Diabetes Care in January 2014.
“Diabetes is a major cause of blindness in adults, and improving blood sugar control lowers but doesn’t remove the risk,” says Daniel E. Hale, MD, an endocrinologist, professor of pediatrics, and division chief of pediatric endocrinology and diabetes at the University of Texas Health Science Center in San Antonio.
Symptoms of Diabetic Retinopathy to Watch For
Symptoms of proliferative diabetic retinopathy affect both eyes and include:
  • Floaters — spots, dots, and strings in your vision
  • Vision that shifts from clear to blurry
  • Inability to see part or all of your field of vision
  • Inability to see well at night
  • Colors that lose their sharpness or tone
  • Loss of visual acuity
  • Blurring vision
To help reduce the risk for eye complications, the American Diabetes Association recommends an annual dilated eye exam for people who have diabetes, regardless of whether they have symptoms or not. In a dilated exam, an eye doctor puts medicated drops in your eyes to dilate your pupils, allowing him or her to best see and examine your retina.
Diagnosing and Treating Diabetic Retinopathy
A diagnosis of diabetic retinopathy is based on results of a comprehensive eye exam. This includes a dilated eye exam and a visual acuity test that measures your ability to see letters, shapes, or numbers on an eye chart at set distances. 
Treatments for diabetic retinopathy include:
  • Injections. Medications, including steroids and anti-vascular endothelial growth factor (anti-VEGF), help stop the growth of new blood vessels and may slow swelling and bleeding. These injections may somewhat restore lost vision and prevent bleeding in the eye, according to a review of research published in the November 2014 issue of the journal Cochrane Database of Systemic Reviews.
  • Laser treatment. Called photocoagulation, this treatment may be used to stop bleeding and slow swelling. According to another report in the November 2014 issue of the Cochrane Database of Systemic Reviews, this approach may slow progression of the disease and protect against vision loss over time.
  • Vitrectomy. This is a surgical procedure to remove blood or scar tissue from the eye. Research published in 2011 in the journal Cochrane Database of Systemic Reviews states that vitrectomy may protect vision in some people, particularly those who've had diabetes for less than 20 years.
Although treatments can't cure diabetic retinopathy, they can help slow its progression and protect your vision. The earlier you can begin to prevent or slow diabetes-related eye damage, the better you’ll be able to help preserve your vision for life.