Retinal Oxygen Extraction in Patients with Primary Open-Angle Glaucoma.

Objective: To compare total retinal oxygen extraction between patients with primary open-angle glaucoma (POAG) and healthy control subjects. Design: A prospective, single-center, cross-sectional, case−control study performed at the Medical University of Vienna. Subjects: Forty patients with POAG and 40 age- and sex-matched control subjects. Methods: Total retinal blood flow was measured using Doppler optical coherence tomography (OCT). Retinal arterial and venous oxygen saturation was measured using reflectance spectroscopy. From these parameters, oxygen content in the retinal arterial and venous circulation as well as total retinal oxygen extraction were calculated. Results: Total retinal blood flow was lower in POAG (25.2 ± 6.7 µL/min) as compared to healthy control subjects (35.6 ± 8.3 µL/min, p < 0.001). Retinal arterial oxygen content was not different between the two groups (0.18 ± 0.01 mL(O2)/mL in both groups, p < 0.761), but retinal venous oxygen content was higher in POAG (0.15 ± 0.01 mL(O2)/mL) than in healthy controls (0.14 ± 0.01 mL(O2)/mL p < 0.001). Accordingly, retinal oxygen extraction was reduced in POAG (0.8 ± 0.3 µL(O2)/min as compared to healthy controls: 1.4 ± 0.4 µL(O2)/min, p < 0.001). There was a significant association between total retinal blood flow and total retinal oxygen extraction with measures of structural and functional damage (p < 0.001 each). Conclusions: This study indicates that POAG is associated with a reduction in total retinal oxygen extraction linked to structural and functional damage of the disease. Since the technology is non-invasive, it allows for longitudinal studies investigating to which degree low retinal oxygen extraction is linked to the progression of the disease.