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Night light might shade diabetic retinopathy
By
Sean Henahan
CARDIFF - Sleeping with the lights on might actually slow the course
of
diabetic retinopathy, a new study in The Lancet suggests.
Previous studies have shown that patients with diabetes have impaired
vascular function in many body tissues which include the retina.
Other research has suggested that oxygen deprivation associated
with impaired circulation may play a role in the development of
diabetic retinopathy.
Moreover, the effect of oxygen deprivation appears to take its greatest
toll in the evening hours when the oxygen demand by the rods is
at its highest.
Based on these and other observations, Neville Drasdo MD, PhD, and
colleagues at Cardiff University, Wales, compared the effect of
oxygen inhalation on the amplitude of oscillatory potentials after
dark adaptation in patients with type 2 diabetes and controls. Seven
patients with type 2 diabetes mellitus, but no evidence of retinopathy
participated in the study, together with eight age-matched controls.
The testing revealed that the diabetic patients showed decreased
oscillatory potentials induced by dark adaptation compared to controls.
When the diabetics received additional oxygen, the levels reached
were similar to those seen in the controls. Moreover, the oscillatory
potentials measured in the controls were not affected by the oxygen.
"Since light transmission through closed lids is adequate to
suppress dark adaptation, our findings strengthen the suggestion
that diabetic patients might benefit from a modified cycle of night-time
illumination during sleep to reduce oxygen consumption in the retina,"
Dr Drasdo commented.
The findings in the healthy controls suggest that autoregulation
of the retinal circulation is adequate during dark adaptation in
nondiabetic eyes. The response of the diabetic eyes to oxygen suggested
that the autoregulation was maximal but inadequate.
Electrophysiological findings indicated that the amacrine cells
in the diabetics were subject to hypoxia. This would have placed
the retinal vessels under prolonged nocturnal stress even before
the development of retinopathy, he reported.
Dr Drasdo noted that further support for the hypothesis comes from
the observation that diabetic retinopathy rarely, if ever, develops
in patients with diabetes and retinitis pigmentosa in whom rod function
is lost. He also cites research indicating that reduced colour vision
and contrast sensitivity have been partially reversed with oxygen
inhalation in patients with diabetes.
The research appeared in The Lancet, Volume 359, Issue 9325, 29th
June 2002.
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