Retinal oximetry in primary open-angle glaucoma

Purpose. To determine whether retinal vessel oxygen saturation is affected in primary open-angle glaucoma (POAG) patients. Methods. Retinal oxygen saturation in patients with POAG was measured in retinal vessels with a spectrophotometric retinal oximeter in darkness, and visual fields were obtained. Oxygen tension (Po ₂) was calculated from oxygen saturation values. Statistical analysis was performed using Pearson's correlation and Student's t-test. Results. Mean oxygen saturation in venules was higher in persons with poor visual fields (68% ± 4%, mean ± SD) than in those with good visual fields (62% ± 3%; P = 0.0018). The mean arteriovenous difference in oxygen saturation was lower in persons with poor visual fields (30% ± 4%, n = 9) than in those with good visual fields (37% ± 4%; P = 0.0003; n = 12). No correlation was found between saturation in retinal arterioles and visual field mean defect (n = 31; r = -0.16; P = 0.38). Oxygen saturation in retinal venules correlated positively with worsening visual field mean defect (r = 0.43; P = 0.015). Arteriovenous difference in oxygen saturation decreased significantly as the visual field mean defect worsened (r = -0.55; P = 0.0013). Mean Po ₂ in venules was 38 ± 3 mm Hg. It was significantly higher in persons with poor visual field fields (40 ± 3 mm Hg) than in those with good visual fields (36 ± 2 mm Hg; P = 0.0016). Conclusions. Deeper glaucomatous visual field defects are associated with increased oxygen saturation in venules and decreased arteriovenous difference in retinal oxygen saturation. The data suggest that oxygen metabolism is affected in the glaucomatous retina, possibly related to tissue atrophy.