Acute effects of insulin on aqueous humor flow in patients with type 1 diabetes

PURPOSE: Previous studies reported reduced aqueous humor flow through the anterior segment of the eye in patients with type 1 diabetes. This study investigates whether reduced flow is the result of the diabetic state or of alterations in glucose or insulin concentrations. METHODS: A cross-sectional study, involving patients with type 1 diabetes and healthy controls, measured aqueous flow at different insulin concentrations. Eleven patients with type 1 diabetes (hemoglobin A1C = 7.0 ± 0.3% [mean ± SEM], normal < 6.5) with no microvascular complications and 17 controls were prospectively studied. Controls were studied fasting and during a hyperinsulinemic-euglycemic clamp (insulin 2 mU/kg per minute). Patients with type 1 diabetes were similarly studied during two euglycemic clamp procedures (insulin 0.5 and 2.0 mU/kg per minute). Aqueous flow was measured by fluorophotometry. Pulsatile ocular blood flow and intraocular pressure were measured with a Langham flow probe. RESULTS: Control subjects had no change in aqueous flow during fasting and hyperinsulinemic conditions (3.0 ± 0.1 vs 2.8 ± 0.1 μl per minute). In the patients with type 1 diabetes, aqueous flow was not decreased with hyperinsulinemia, compared with the low insulin state (P = .7). Compared with control subjects, patients with type 1 diabetes had lower aqueous flow during hyperinsulinemia (2.4 ± 0.1 μl per minute, P = .03) and at lower insulin conditions (2.6 ± 0.1 μl per minute, P < .05). No differences in intraocular pressure or pulsatile ocular blood flow were noted between groups or between insulin states within groups. CONCLUSIONS: Aqueous flow is decreased in patients with type 1 diabetes under euglycemic conditions of high and relatively low insulin concentrations, despite the absence of microvascular complications.