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Night Light Could Help Diabetics' Sight

Normal illumination might prevent diabetic retinopathy

FRIDAY, June 28, 2002 (HealthDayNews) -- Having a light on at night may do more than keep the monsters away and get you safely to the bathroom.

Research published in tomorrow's issue of The Lancet suggests that normal levels of illumination at night might help prevent diabetic retinopathy, or damage to the retina which occurs in people who have diabetes and which, in extreme cases, can result in blindness.

Uncontrolled diabetes can lead to a number of complications in addition to retinopathy, including kidney problems and even amputation of feet and limbs. All of these complications ultimately result from impaired blood flow, meaning that different areas of the body don't get enough oxygen.

Although this oxygen deprivation no doubt has much to do with the onset of diabetic retinopathy, no one knows exactly why the problem can get so bad in this particular part of the body.

Scientists have speculated that it's because the inner layers of the retina don't get enough oxygen at night. Rods in the eye, which are responsible for night vision, require more oxygen than any cell in the human body at low levels of illumination.

Research has shown that people with diabetes have reduced activity in these deep, inner areas.

This study looked at the effect of oxygen inhalation on retinal function in seven patients with Type II diabetes. Patients were found to have reduced retinal function before inhaling oxygen and an increase in function of about 31.5 percent after.

"Rods are in the deepest layers of the retina, but our research showed for the first time that the surface layers of the retina, where the retinopathy develops, were subject to hypoxia in people with diabetes after some time in darkness," says Neville Drasdo, study author and a professor in the department of optometry and vision sciences at Cardiff University in the United Kingdom.

If the findings are borne out in future research, there could be major implications for preventing this debilitating disorder.

"The observations shed light on the mechanisms of retinal eye disease in diabetes and suggest the development of retinal damage results, at least in part, from impaired oxygen supply during the dark adaptation at night, a time at which exceptionally high oxygen consumption by the eye rod receptors occurs," says Dr. Fouad Kandeel, director of the department of diabetes, endocrinology and metabolism at City of Hope National Medical Center in Los Angeles.

"The decrease in oxygen supply is due to the presence of small capillary disease. Thus, reducing the high oxygen demand of retinal tissue through limiting the exposure to darkness may help to retard the development of eye retinal disease in the diabetic patients," Kandeel adds.

The jury, though, is still out.

"It has been shown that, depending on the transparency of the closed eyelids, a normal level of illumination (not a night light) would probably be adequate to reduce oxygen consumption by the rods," Drasdo says. "However, we cannot yet advise people to keep lights on throughout the night. The effects of this need further investigation because it might cause some other problems. Research is necessary to determine the best procedure to implement this principle successfully."

What To Do

For more information on diabetic retinopathy, visit the National Eye Institute. Or you can take this diabetic eye quiz at the National Eye Institute.

SOURCES: Neville Drasdo, D.Sc., professor, department of optometry and vision sciences, Cardiff University, Cardiff, United Kingdom; Fouad Kandeel, M.D., Ph.D., director, department of diabetes, endocrinology and metabolism, City of Hope National Medical Center, Los Angeles; June 29, 2002,The Lancet
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