Glucose concentration and retinal function.

The rod and cone systems of the mammalian retina differ in their structure and functional properties as well as in their metabolic characteristics. This article summarizes basic observations on retinal glucose metabolism reflected in retinal electrophysiology. Metabolic factors might be related to the complex pathogenesis of diabetic retinopathy. Effects of changing glucose concentration and, independently, of insulin on retinal responses obtained in an isolated mammalian eye preparation in vitro and also in vivo are presented. Electron microscopy (EM)-histochemical data reveal a distinctive distribution of glycogen in glia and in various subclasses of neurons in the cat retina. Low glucose, corresponding to hypoglycemia in vivo, affected the light-evoked electrical responses from the rod system, but not from the cone system in vitro. This could be confirmed in the anesthetized cat under glucose clamp conditions. Insulin had no influence on physiological retinal function, except under conditions of low glucose, where it enhanced the reduction in b-wave amplitude. This effect is interpreted as a sign of increased glucose utilization by the retinal Müller (glial) cells.