Retinal vessel oxygen saturation under flicker light stimulation in patients with nonproliferative diabetic retinopathy

We investigated the response of retinal vessel diameters and oxygen saturation to flicker light stimulation of neuronal activity in patients with diabetic retinopathy. We included 18 patients with nonproliferative diabetic retinopathy (mean age 62.2 ± 8.3 years, diabetes type 1 in 4 patients and type 2 in 14, hemoglobin A1c 7.7 ± 0.9%, duration of diabetes 24.1 ± 9.3 years) and 20 age-matched healthy controls (age 66.7 ± 10.3 years). Dual wavelength (548 and 610 nm) fundus images were taken before and during luminance flicker stimulation (12.5 Hz, modulation depth > 1:25) for 90 seconds. Diameters (central retinal arterial [CRAE] and venous [CRVE] equivalents) and oxygen saturation (SO(2)) were determined, and averaged for all arterioles and venules in an annular area centered at the optic disk. Flicker light increased CRAE, CRVE, and venous SO(2) by 0.6 ± 6.6%, 2.7 ± 6.1%, and 2.0 ± 2.4% (P < 0.05), respectively, in the patients as well as 4.7 ± 8.4% (P < 0.05), 8.7 ± 5.2% (P < 0.05), and 4.2 ± 3.5% (P < 0.05), respectively, in the controls. The arterial SO(2) remained unchanged in both groups. The increase of the venous SO2 correlated significantly (P = 0.027) with that of the CRAE. There was a trend (P = 0.06) for lower increase of the venous SO(2) with higher body mass index. Our results support the thesis of an impaired regulation of oxygen supply to the diabetic retina. Whereas in healthy subjects the stimulation of neuronal activity increases the vascular diameters and, subsequently, the oxygen supply, this increase is reduced in diabetic retinopathy. This may hint at the role of endothelial dysfunction in the etiology of the disease.