Correlation of retinal vessel oxygen saturation with structural and functional damage in glaucoma

Objective To determine if retinal oxygen metabolism is different in glaucoma patients compared to healthy subjects and to determine if retinal vessel oxygen saturation is correlated with structural and functional damage in glaucoma patients. Methods This case control study included 28 patients (35 eyes) with primary open-angle glaucoma and 27 healthy individuals (41 eyes). Visual fields were measured with a Humphrey field analyzer. Optical coherence tomography (OCT) was performed to detect the thickness of the retinal nerve fiber layer (RNFL) in glaucoma patients. Retinal vessel oxygen saturation was measured in glaucoma patients and healthy individuals with a non-invasive spectrophotometric retinal oximeter. Statistical analysis was performed using independent t-test and Pearson′s correlation. Results There was no significant difference in retinal arteriole oxygen saturation between glaucoma patients and healthy individuals. However, the oxygen saturation in venules was higher and the arteriovenous difference was lower in glaucoma patients (t=4.017, P<0.001; t=-4.431, P<0.001). Retinal arteriolar oxygen saturation was not associated with age, intraocular pressure, blood pressure, cup-to-disc ratio, mean deviation (MD), visual field index (VFI), or RNFL thickness in glaucoma patients. The retinal oxygen saturation in both the venules and arteriovenous (AV) difference was not correlated with age, intraocular pressure, or blood pressure in glaucoma patients. Retinal venous oxygen saturation was positively correlated with the cup-to-disc ratio (r=0.418, P=0.012) and MD (r=0.504, P=0.002) and negatively correlated with RNFL thickness (r=-0.514, P=0.002) and VFI (r=-0.470, P=0.004) in glaucoma patients. On the other hand, the AV difference was negatively correlated with the cup-to-disc ratio (r=-0.390, P=0.021) and MD (r=-0.478, P=0.004) and positively correlated with RNFL thickness (r=0.385, P=0.022) and VFI (r=0.449, P=0.007) in glaucoma patients. Conclusion Severe glaucomatous damage is associated with increased oxygen saturation in venules and a decrease in the AV difference in retinal oxygen saturation, suggesting that reduced retinal oxygen consumption is related to the atrophy of the retinal nerve fibers. Key words: Glaucoma; Retinal vessel oxygen saturation; Cup-to-disc ratio; Visual fields; Retinal nerve fiber layer thickness