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

PURPOSE: Previous studies reported reduced aqueous humor flow through the a nterior segment of the eye in patients with type 1 diabetes. This study inv estigates whether reduced flow is the result of the diabetic state or of al terations in glucose or insulin concentrations. METHODS: A cross-sectional study, involving patients with type 1 diabetes a nd healthy controls, measured aqueous flow at different insulin concentrati ons. Eleven patients with type 1 diabetes (hemoglobin A1C = 7.0 +/- 0.3% [m ean +/- SEM], normal < 6.5) with no microvascular complications and 17 cont rols were prospectively studied. Controls were studied fasting and during a hyperinsulinemic-euglycemic clamp (insulin 2 mU/kg per minute). Patients w ith type 1 diabetes were similarly studied during two euglycemic clamp proc edures (insulin 0.5 and 2.0 mU/kg per minute). Aqueous flow was measured by fluorophotometry. Pulsatile ocular blood flow and intraocular pressure wer e measured with a Langham flow probe. RESULTS: Control subjects had no change in aqueous flow during fasting and hyperinsulinemic conditions (3.0 <plus/minus> 0.1 vs 2.8 +/- 0.1 mul per mi nute). In the patients with type 1 diabetes, aqueous flow was not decreased with hyperinsulinemia, compared with the low insulin state (P = .7). Compa red with control subjects, patients with type 1 diabetes had lower aqueous flow during hyperinsulinemia (2.4 +/- 0.1 mul per minute, P = .03) and at l ower insulin conditions (2.6 +/- 0.1 mul per minute, P < .05). No differenc es in intraocular pressure or pulsatile ocular blood flow were noted betwee n groups or between insulin states within groups. CONCLUSIONS: Aqueous flow is decreased in patients with type 1 diabetes und er euglycemic conditions of high and relatively low insulin concentrations, despite the absence of microvascular complications. (Am J Ophthalmol 2001; 132:321-327. (C) 2001 by Elsevier Science Inc. All rights reserved.).