Effects of hypoxemia on the electroretinogram in diabetics

To identify any relationship between retinal dependence on oxygen and the presence or absence of retinopathy in a group of patients with the same duration of diabetes, based on the proposal that diabetic retinopathy results from long-term adaptation to the Crabtree effect, i.e., reduction of oxidative phosphorylation caused by increased intracellular glucose concentrations.

Electroretinograms were recorded on 17 patients with insulin-dependent diabetes (of 15 to 17 years duration) and 10 healthy controls. Recordings were made under normal conditions and then after 4 min of hypoxemia (oxygen saturation, 80%). Retinopathy status was assessed from fundus photographs.

Electroretinogram b-wave amplitudes of seven patients without retinopathy were reduced to 69% by the hypoxemia compared to a reduction to 88% for 10 patients with retinopathy (p = 0.039).

The relative sensitivity to hypoxemia of patients without retinopathy suggests greater dependence on oxidative phosphorylation than in patients with retinopathy. The results appear to be consistent with the Crabtree effect hypothesis. Downregulation of tissue oxygen consumption by the Crabtree effect would lead to a reduction of retinal blood flow by autoregulation and to a reduced concentration of adenosine triphosphate in the retina.