Hyperglycemia impairs retinal oxygen autoregulation in normal and diabetic dogs

Preretinal oxygen tensions were measured continuously using microelectrodes in four normal dogs and four dogs made diabetic with alloxan. The latter were kept under poor control for 8 months. Glucose administered intravenously in 30 to 90 sec to all the dogs when they were normoglycemic caused an immediate increase in preretinal oxygen tension lasting approximately 10 min. When the dogs were given 100% oxygen to breathe, their preretinal oxygen tensions increased. This increase in preretinal oxygen tension was 36.6 +/- 8.5 mmHg (+/-SE) when the animals were normoglycemic and 63.5 +/- 9.2 mmHg when the animals were made hyperglycemic. This suggests that hyperglycemia impairs oxygen autoregulation. Moreover, the diabetic dogs appeared to exhibit a larger preretinal oxygen tension increase than normal dogs when both were given 100% oxygen to breathe. The small number of animals studied, however, makes a comparison between the two groups difficult. These data lead one to speculate that in diabetes there may be an impairment of the normal retinal vascular homeostasis. This could play a role in both the development and in the severity of diabetic retinopathy.