Investigation of blood flow regulation and oxygen saturation of the retinal vessels in primary open-angle glaucoma

To examine the supply of oxygen to the retina in primary open-angle glaucoma (POAG).

Forty-one patients with primary open-angle glaucoma (mean age 64.1 ± 12.9 years) and 40 healthy subjects (63.6 ± 14.1 years) were included. Fundus images, centered at the optic disc, were taken using the Retinal Vessel Analyzer (RVA). The vessel diameters were calculated as central retinal artery (CRAE) and vein equivalent (CRVE) from diameter measurements in the peripapillary vessels. The oxygen saturation of the arteries and veins was investigated employing a two-wavelengths technique. After the measurement at baseline, the vascular response to flicker light exposure was measured.

In glaucoma patients the mean oxygen saturation of the retinal veins at baseline was higher than in the healthy controls (64.36 ± 7.11 vs. 59.78 ± 8.47, p = 0.01), whereas the mean arteriovenous oxygen saturation difference was lower (33.07 ± 5.24 vs. 37.53 ± 6.95, p = 0.002). The arterial oxygen saturation as well as the arterial and venous diameters showed no difference between the groups. The increase of the CRVE during flicker light stimulation (3.72 ± 3.29 % vs. 5.43 ± 4.04, p = 0.039), as well as the change of the venous oxygen saturation (2.08 ± 3.74 % vs. 4.18 ± 3.88 %, p = 0.016) and the arteriovenous saturation difference (−2.1 ± 3.31 % vs. −4.43 ± 3.6 %, p = 0.003) were smaller in POAG patients than in the healthy group.

The reduction in the arteriovenous difference in oxygen saturation in POAG patients might show a decreased oxygen demand of the retina caused by the glaucomatous loss of neuroretinal tissue. The lower extent of the flicker light-induced change of the diameter of retinal veins and the venous oxygen saturation could indicate an impairment of blood flow regulation.