Preventing Vision Problems Associated With Diabetes
Lloyd Paul Aiello, M.D., Ph.D. Associate Director, Beetham Eye Institute, Joslin Diabetes Center; Associate Professor of Ophthalmology, Harvard Medical School
About half of all people with diabetes eventually develop some problem with their eyes or vision. They are more likely than others to get cataracts or glaucoma. The most feared eye complication, however, is diabetic retinopathy, which is relatively common and potentially sight threatening. But there’s a lot we can do to preserve vision, even for those with diabetic retinopathy.
People with diabetes can help preserve their vision—as well as reduce many of the complications associated with diabetes—by controlling their blood glucose, blood pressure and cholesterol and triglyceride (“lipid”) levels. Even if they do not yet have diabetic eye complications, they need to have routine lifelong eye checkups at least once a year to catch any problems that start to develop. These examinations are critical because a person with eye complications often does not experience any symptoms that indicate damage until it’s too late to undo the damage. The presence of eye disease usually requires more frequent eye examinations.
Don’t Wait for Symptoms
Diabetic retinopathy occurs when the tiny blood vessels inside the retina—the tissue at the back of the eye that sends images to the brain—become damaged. There are usually no symptoms at this early “nonproliferative” stage. Essentially all people with diabetes will eventually develop some changes in the retina, usually within 20 years of diabetes onset.
In two-thirds of cases, this type of retinopathy progresses to the “proliferative stage,” although research shows that intensive glucose and blood pressure control can delay the onset of disease and slow its progression. In the proliferative stage, the retina forms new vessels in an attempt to circumvent nonfunctioning blood vessels. These new vessels, however, are abnormal, fragile and bleed readily. If the condition is treated with laser photocoagulation when the abnormal vessels are in their early stages, severe vision loss can be prevented in about 95 percent of cases. The laser scars the retina, causing the vessels to regress, which prevents subsequent bleeding and pulling on the retina. Since the laser destroys some areas of the retina, there may be side effects of treatment—such as reduced side or night vision—but central vision is retained far better than if the patient receives no treatment at all.
Diabetic macular edema, however, is a different story. Diabetes can cause the retinal vessels to leak, leading to swelling of the retina. If this swelling occurs in the small area in the center of the retina called the macula, the condition is called macular edema. Vision can decline because this area of the retina is responsible for central vision. Laser treatment is also used for this condition but is less successful than when used for new vessels. Treatment reduces the chance of vision worsening by only half, and, even when successful, is usually not associated with improved vision.
Promising New Drugs
Clearly we’d like to have better treatments or multiple therapeutic approaches to offer patients. Fortunately, there are potential new medical therapies in the pipeline. It’s an exciting time because many of these new drugs have emerged from recent and very specific understandings of the cellular mechanisms that underlie diabetic eye problems. Whether any will have an effect on preserving vision, we don’t yet know. We first need to find out if they’re effective and what side effects they may cause.
One approach that I’ve been studying involves a PKC inhibitor, a substance that blocks the action of an enzyme called protein kinase C (PKC). My colleagues at Joslin Diabetes Center and I have learned that PKC becomes activated early in diabetes by high glucose levels. Together we found that PKC triggers blood vessel dysfunction and that VEGF (vascular endothelial growth factor), which is thought to signal the formation of the abnormal blood vessels, needs PKC activity to be effective.
So far, results have shown that PKC inhibitors (taken as a pill) do not seem to stop the progression from nonproliferative to proliferative retinopathy, but might help with macular edema and vision loss. If proven effective, such a treatment would offer a new option to address a condition for which our existing treatment is not effective for everyone. The results of large clinical trials will be completed within the next two years.
Other approaches now being tested include inhibitors of VEGF and other growth factors like Insulin-like Growth Factor-1(IGF-1), as well as steroids injected into the eye. For example, a product called Macugen® blocks VEGF and, when injected into the eye, appears in early patient studies to reduce macular edema and improve vision. A new steroid formulation designed specifically for the eye is being investigated by the Diabetic Retinopathy Clinical Research Network in patients for its potential effect in reducing macular edema and actually improving vision.
These new treatments under investigation offer great hope, but results of careful studies are needed before we know if any will be truly helpful. Participation in well designed clinical trials is important for future care. As for current eye care, everyone with diabetes should get annual eye checks and keep blood glucose, blood pressure and cholesterol in good control.
Page last updated: April 23, 2014