Abstract

Objective: Stimulation of the retina with flickering light increases retinal vessel diameters in humans. Nitric oxide is a mediator of the retinal vasodilation to flicker. The reduction of vasodilation is considered as an endothelial dysfunction. We investigate the response of retinal vessels to flickering light in diabetic patients in different stages of diabetic retinopathy (DR).

Research Design and Methods: We studied 53 healthy volunteers, 68 type 1 and 172 type 2 diabetic patients. The diameter of retinal vessels was measured continuously on-line with the Dynamic Vessel Analyzer (DVA). The diabetic retinopathy was classified using ETDRS-criteria. Changes in vasodialtion are expressed as percentage change over baseline values.

Results: After adjusting for age, sex and antihypertensive treatment the response of retinal arterioles to diffuse luminance flicker was significantly diminished in patients with type 1 diabetes mellitus compared to healthy volunteers. The vasodilation of retinal arterioles and venoles decreased continuously with increasing stages of diabetic retinopathy. The retinal arterial diameter change was 3.6±2.1% in control group, 2.6±2.5% in no DR group, 2.0±2.7% in mild nonproliferative DR, 1.6±2.2% in moderate nonproliferative DR, 1.8±1.9% in severe nonproliferative DR and 0.8±1.6 % in proliferative DR group.

Conclusions: Flicker responses of retinal vessels are abnormally reduced in diabetic patients. This decreased response deteriorated with increasing stages of retinopathy. The response was already reduced before clinical appearance of retinopathy. The noninvasive testing of retinal autoregulation with DVA might prove to be of value in early detection of diabetic vessel pathology.