Do Certain Genes Lead to Vision Loss?
Lucia Sobrin, MD, MPH
Lucia Sobrin, MD, MPH
Retina Specialist, Massachusetts Eye and Ear Infirmary
|ADA Research Funding
Clinical Translational Award
The retina might well be your body's most vital .07 square inches. A thin layer of cells just one-hundredth of an inch thick, the retina is literally the film in your eye's camera. Sitting at the back of your eyeball, it contains millions of nerves responsible for capturing light and sending signals to the brain.
Any damage to that fragile tissue, and your vision can be impaired or disappear entirely. When it comes to eye damage, diabetes is one of the worst culprits. The tiny blood vessels that feed the retina are particularly sensitive to harm. "The most sight-threatening complication of diabetes is diabetic retinopathy," says Lucia Sobrin, MD, MPH, an eye specialist at the Massachusetts Eye and Ear Infirmary in Boston. "It damages blood vessels slowly, in the same way it damages blood vessels in the kidney and heart. There's a lack of blood flow, and abnormal growth [of blood vessels] and bleeding in the eye."
In fact, diabetic retinopathy is the No. 1 cause of irreversible vision loss in people 20 to 65. It's possible to slow it, and sometimes even halt it completely, but once it develops the damage can't be repaired. "If you control your blood sugars, blood pressure, and cholesterol really well, you can reduce the damage in the eye," Sobrin says. "But there are patients who, despite doing all those things, still get damage to their eye."
Retinopathy is diagnosed with a dilated eye exam (which can find the problem long before symptoms occur) or when symptoms appear. They can vary from a slow loss of vision to sudden, dramatic changes in cases where a blood vessel suddenly bursts. As blood vessels leak into the fluid of the eye, black spots, sometimes called "floaters," can appear in the field of vision. Retinopathy can be treated, either with drugs injected into the eye or with laser surgery.
But it can't usually be reversed. And statistics indicate that the risk of developing eye problems isn't evenly distributed. "Some ethnic groups develop diabetic retinopathy more often," Sobrin says. African Americans, for example, are much more likely than whites to have retinopathy. "That," Sobrin says, "suggests that some people are genetically predisposed."
If that's true, there must be a gene or combination of genes that make some people more vulnerable than others. To test the possibility, Sobrin has set up an experiment with funding from the American Diabetes Association. She is recruiting 450 people with diabetes from ophthalmology clinics in Jackson, Miss., and Boston.
About 350 of the people in the study are African Americans with severe diabetic retinopathy. The other 100 are the control group, all of whom have had diabetes for 10 years or more but haven't developed eye problems.
To see if vulnerability to retinopathy is genetic, Sobrin is comparing the DNA of the African Americans with eye damage to the control group. Although the study focuses on an ethnic group with a high risk of retinopathy, the study's results would be broadly applicable. "The genes we find would probably have relevance in people of any ethnicity," Sobrin says.
Researchers record each participant's height and weight, and take blood samples and pictures of their eyes. Using DNA taken from the blood samples, Sobrin hopes to quickly identify any genetic differences between the people with and without retinopathy—and thus isolate possible genetic markers for the disease.
If something stands out, it could help doctors—and patients—in the future. "If you found a gene that had a really strong effect, you could in theory screen patients and follow them more closely," Sobrin says. "If we can narrow it down and find the gene that's responsible, it could be a target for treatment eventually."
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In the meantime, while you may not be able to change your genetic makeup, it's still possible to affect the odds. Statistics show that timely treatment of retinopathy and follow-up care reduce the chances of blindness by 95 percent.
And focusing on the basics is a good way to make sure you'll see the world clearly for a long time to come. An annual dilated eye exam is recommended, with more frequent checkups if retinopathy is quickly progressing or you notice vision changes. While you can't control the length of time you have diabetes, which is the strongest risk factor for developing diabetic retinopathy, Sobrin says that keeping close tabs on the risk factors you can control—blood pressure, cholesterol, and blood glucose—will improve your odds of safeguarding your vision.