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Kaija Polak, MD; Susanne Dallinger, MD; Elzbieta Polska, MD; Oliver Findl, MD; Hans-Georg Eichler, MD; Michael Wolzt, MD; Leopold Schmetterer, PhD

Arch Ophthalmol. 2000;118:55-59.

Background  Insulin induces vasodilation in several tissues, including skeletal muscle and kidneys.

Objective  To investigate whether insulin may contribute to ocular blood flow regulation.

Methods  The study was performed in a balanced, randomized, placebo-controlled, single-masked, 3-way, crossover design in 9 healthy male subjects. Each subject received 2 doses of insulin (1.5 or 3 mU/kg per minute) or placebo on 3 different study days. Measurements of fundus pulsation amplitude with laser interferometry to assess pulsatile choroidal blood flow, of retinal blood flow with the blue-field entoptic technique, and of mean blood flow velocity in the ophthalmic artery with Doppler sonography were performed under euglycemic clamp conditions over 120 minutes.

Results  Hyperinsulinemia significantly increased fundus pulsation amplitude (1.5 mU/kg per minute: 8.7% ± 1.1% vs baseline; 3 mU/kg per minute: 13.2% ± 2.3% vs baseline; P<.001 vs placebo [analysis of variance]) and mean blood flow velocity (1.5 mU/kg per minute: 10.0% ± 4.3% vs baseline; 3 mU/kg per minute: 6.6% ± 3.5% vs baseline; P = .03 vs placebo). Retinal blood flow did not increase during administration of insulin (1.5 mU/kg per minute: 6.4% ± 8.0% vs baseline; 3 mU/kg per minute: 8.0% ± 5.1% vs baseline; P = .99 vs placebo). Neither the effect in the choroid nor that in the ophthalmic artery was dose-dependent.

Conclusion  Hyperinsulinemia significantly increases choroidal blood flow and mean blood flow velocity in the ophthalmic artery. By contrast, retinal blood flow was not influenced by hyperinsulinemia. The maximum effective dose of insulin for ocular hemodynamics is likely to be within the physiological range.

From the Department of Clinical Pharmacology (Drs Polak, Polska, Eichler, Wolzt, and Schmetterer), the Institute of Medical Physics (Dr Schmetterer), and the Department of Ophthalmology and Optometry (Dr Findl), Vienna University, Vienna, Austria.

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