An Eye Test for Diabetes
Diabetes messes with the body’s metabolism, which can result in devastating complications like nerve damage, kidney disease, and vision loss.
By capturing a snapshot of the eye, scientists in Michigan say that they can pick up telltale signs of metabolic stress in the retina caused by diabetes. They say that the new imaging technology may offer a quick, noninvasive way of detecting the disease early and monitoring its progress.
“With just a minute in an optometrist’s office, you might be able to detect metabolic stress in the eye, refer the patient to an endocrinologist, and get a diagnosis,” says Howard Petty, a biophysicist and imaging expert at the University of Michigan’s Kellogg Eye Center and one of the authors of a study that appears in the latest issue of the Archives of Ophthalmology.
The study focused on patients with diabetes, but Petty says that the screening technology should be able to identify people with prediabetes–a condition in which blood glucose levels are higher than normal and that often progresses to full-blown diabetes. The researchers are beginning clinical trials this fall, using the system on diabetics and prediabetics.
“It’s an intriguing idea that you could detect early diabetes by looking for the changes that result from blood sugar, in the eye,” says John Buse, president of Medicine and Science at the American Diabetes Association, who was not involved in the work.
Petty, together with Victor Elner and other colleagues at the University of Michigan, used a sophisticated camera system coupled with customized imaging software to detect fluorescence given off by oxidized proteins in dying cells in the retina. The 21 diabetics in their study had elevated levels of autofluorescence from retinal flavoprotein, compared with healthy age-matched control subjects. Diabetics that had –damage to the retinal tissue that can causes blindness–had even higher levels of fluorescence than diabetics without the condition.
Petty and his colleagues have already used their imaging system to detect pseudotumor cerebri (PTC), a disorder that causes symptoms similar to those of a brain tumor. They also plan to test the system on patients with macular degeneration and glaucoma.
The correlation between elevated autofluorescence and diabetes is “an interesting observation,” says Lois Jovanovic, CEO and chief scientific officer of Sansum Diabetes Research Institute, in Santa Barbara, CA. “But it raises more questions than it answers.” Jovanovic wants more studies to be done, with more data on blood sugar levels in study subjects, to prove that high fluorescence measurements are really a result of metabolic stress and not of fluctuations in blood glucose. She also wants to see the results of eye tests in people with type 1 diabetes compared with the much more common type 2. Petty says that the effects on the eye would be the same.
Even if the eye test proves effective in clinical trials, it’s unlikely to replace blood sugar screening, the test most commonly used to detect diabetes. However, it may provide a useful early-warning tool. To detect prediabetes, physicians use the more sensitive glucose tolerance test, a time-consuming and expensive test in which blood glucose levels are monitored before and after a patient is given a sweet drink.
Petty hopes to make the eye imaging system inexpensive enough that it could be used by optometrists, not just ophthalmologists, to identify people who may have prediabetes. Glucose tolerance testing would confirm the diagnosis. “Hopefully, we can find out who these patients are and get them into the right treatment and care,” Petty says.
Petty believes that the technology could motivate people to take better care of their health because “you can tell someone, ‘You’re sliding toward the edge of the cliff, and here’s the data that says so.’”
Eye tests could also be used to monitor diabetic patients, Petty says, and assess the effects of drug treatments and lifestyle changes. Diabetics can lose “a substantial fraction–up to 50 percent–of their retinal cells” before they’re aware of vision problems, Petty says, because the brain adjusts to the input from the eyes–up to a certain point. “Once you’re beyond that threshold, right now … you really can’t get [vision] back,” he adds.
Petty and his colleagues are now having a much smaller version of their first eye imaging system built. It will be easier to use, and unlike the current version, it won’t require a patient’s eyes to be dilated. Petty and Elner have filed for patents and formed a company, OcuSciences, to commercialize the technology.
“The application for diabetes is really staggering when you think about it,” Petty says, “because there are so many diabetics and prediabetics in this country.”
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