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Light nights might prevent blindness in diabetics

00:01 28 June 02

Sleeping with the lights on could prevent diabetic retinopathy, a leading
cause of blindness, say scientists in Wales.

Neville Drasdo and colleagues at Cardiff University say they have confirmed
a long-standing hypothesis that the retinas of people with diabetes are
deprived
of oxygen at night. This could cause damage to the light-sensitive region,
they say.

Oxygen deprivation seems to happen when the retinal cells become adapted to
the dark, and increase their oxygen demand. The team measured a small
electric
current from cells within the retina - an indicator of how healthy the cells
are. This current was reduced in diabetics when their retinas were
dark-adapted.
Allowing the patients to breathe oxygen brought the activity back to a
healthy level.

A normal retina can just about cope with the extra oxygen demand, but it
seems to be too much for diabetics, says Drasdo. It is not clear why, he
adds -
but diabetics do have circulatory problems, and even slightly damaged blood
vessels might not be able to deliver sufficient oxygen to the retina at
times
of high demand. This stress could trigger further changes in the blood
vessels.

Whatever the precise reason, avoiding dark adaptation might prevent that
retinal cell damage, they say. And they think normal room illumination, even
with
the eyes closed, would be sufficient to achieve that. "This should be
investigated as a matter of urgency," says Drasdo. "Diabetic retinopathy is
an enormous
problem."

Small study

Between one quarter and one half of diabetics go on develop retinopathy.
Treatments are available. But within the UK working population, diabetic
retinopathy
is the most common cause of blindness.

Rick Ferris of the National Eye Institute in Bethesda, Maryland, agrees the
findings are interesting. But he cautions that it is just a small study, of
just seven patients, and there is no direct evidence yet that continuous
lighting could prevent the problem. "It is far too early to make a
generalised
recommendation that persons with diabetes should sleep with the lights on,"
he says.

The researchers agree. "Long term exposure to illumination during sleep
could possibly have some undesirable effects," says Rachael North, a
coauthor of
the study.

For example, photoreceptors shed their pigment on a daily cycle. If the
cells were constantly light-adapted, this process might be disrupted.
Constant light
might also interfere with a person's sleep pattern and cause psychological
problems, she suggests.

Journal reference: Lancet (vol 359, p2251)

Helen Phillips

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