Hypoglycemia Increases Ischemic Retinal Injury
Issue 218 Item 8

Hypoglycemia increases the injury associated with pressure-induced retinal ischemia in a rat model. This could have important implications for patients with diabetic eye disease.

Dr. N. N. Osborne and colleagues, from Oxford University in the UK, measured the effects of low blood sugar, also called hypoglycemia, on rats with eye injury due to low blood flow.

In tissue cultures, hypoglycemia increased the amount of nerve cell death that occurred when oxygen was unavailable, a condition that can occur with low blood flow, the authors report. Moreover, retinal function was more impaired in hypoglycemic rats than in other rats.

The eye injury observed in hypoglycemic rats was considerably more severe that of other rats, the authors note. However, in the absence of low blood flow, hypoglycemia did not seem to damage the eye.

So how does hypoglycemia interact with low blood flow to make eye damage worse? When low blood flow occurs, cells often become more reliant on sugar as an energy source, the authors note. Therefore, if sugar levels are low, the cells may not be able to meet their energy requirements, possibly resulting in cell death.

The new findings may help explain why diabetic eye disease often gets worse when patients are first getting their sugar levels under control and low levels are more likely to occur.

"These findings," the authors conclude, "are consistent with the notion that glucose is an important energy substrate for the ischemic retina and indicate that low blood glucose, although beneficial in terms of retarding the progression of diabetic retinopathy, can compromise the ability of the retina to metabolically compensate during periods of low oxygen availability." Br J Ophthalmol 2004;88:816-820.

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