Macular blood flow response to acute reduction of plasma glucose in diabetic patients measured by the blue light entoptic technique.

The response of retinal blood flow to acute reduction in plasma glucose levels was studied in 20 poorly controlled type I diabetic patients. Perifoveal flow velocity was determined, using the blue-light entoptoscope, and arterial calibers measured, using a computer-aided digitizing system. Mean plasma glucose level was lowered from 17.7 +/- 4 to 7.0 +/- 1 mmol/l after a subcutaneous insulin infusion and measurements taken at both glucose levels. The autoregulatory change induced by breathing 60% oxygen at the two plasma glucose levels also was compared. Mean flow velocities were 0.54 +/- 0.28 mm/sec at a high plasma glucose level compared with 0.55 +/- 0.32 mm/sec at a low plasma glucose level, whereas hyperoxia reduced these by 16.58 and 16.71%, respectively. No significant difference in the responses of arterial diameters to hyperoxia between the two glucose levels was found. The authors conclude that acute reduction in plasma glucose level in this group of patients is not associated with significant changes in macular blood flow or in alteration in autoregulation.