Oxygen demand in glaucoma patients: influence of age, vascular dysregulation and oxidative stress

Abstract

PurposeTo evaluate the relationship between vascular dysregulation and retinal oxygen consumption in glaucoma patients.MethodsRetinal vessel oxygen saturation was measured in 46 eyes of 34 Caucasian individuals with primary open‐angle glaucoma and in 21 eyes of 17 age‐matched controls using the oximetry tool of Retinal Vessel Analyser (RVA: IMEDOS Systems UG, Jena, Germany). The mean oxygen saturation of the major arterioles (A‐SO2) and venules (V‐SO2), as well as the corresponding A‐V SO2 difference, were calculated. Within glaucoma patients, retinal vascular responsiveness to flicker light (RVA) was measured, as well. Glaucoma patients were grouped according to their median arteriolar and venular vascular responsiveness, as well as to their median age (68y) and gender. In addition, we calculated the mean retinal oxygen consumption (O2‐C) per micron of nerve fibre layer thickness, O2‐C [%/µm] by dividing the mean AV SO2 with the mean RNFL thickness.ResultsIn glaucoma patients, A‐SO2 and V‐SO2 were significantly increased and their difference decreased, when compared to controls (p = 0.017; linear mixed‐effects model). Whereas V‐SO2 (p = 0.697) and A‐V SO2 (p = 0.674) were not influenced by age, A‐SO2 was severely reduced (94.70 ± 4.01%) and the O2‐C significantly increased (0.50%/µ; ±0.08) in elderly glaucoma patients, than in younger glaucoma patients (98.17 ± 2.8% (p = 0.007), correspondingly 0.43 ± 0.04%/µm (p = 0.004)). Patients with reduced venular vascular responses (≤2.90%) had significantly higher O2‐C (0.49 ± 0.08%/µm, respectively 0.43 ± 0.06%/µ; p = 0.027). Higher O2‐C in glaucoma patients correlated negatively with the neuroretinal rim area (p < 0.001) and with the RNFL thickness (p = 0.017), and positively with the mean defect of the visual field (p = 0.011).ConclusionsReduced venular vascular responsiveness and increased age in glaucoma were associated with increased O2‐C, whereas the mean SO2 values were not related to age‐ and flicker responses. Thus, ganglion cells axons in glaucomatous eyes with vascular dysregulation are prone to consume more O2 (O2‐C [%/µm]), than eyes with normal flicker responsiveness. Furthermore, the increase in oxidative stress seems to contribute to progression of glaucomatous damage.