A high oxygen demand in normal tension glaucoma

Abstract

PurposeTo evaluate relationship between vascular dysregulation and retinal oxygen demand in normal tension glaucoma (NTG).MethodsRetinal vascular responses of 27 eyes of 18 Caucasian (10♀ :8♂) individuals with NTG were measured. Subjects were grouped based on their median vascular responsiveness. In each group, retinal vessel oxygen saturation was measured in arterioles (A‐SO2) and in venules (V‐SO2) within the peri‐papillary annulus with the oximetry tool of Retinal Vessel Analyser (IMEDOS Systems UG, Jena, Germany).Retinal nerve fiber layer thickness (RNFL) was measured with spectral domain optical coherence tomography (Carl Zeiss Meditec, Dublin, CA, USA) and visual field (VF) with Octopus perimeter (Haag‐Streit International, Switzerland). Retinal oxygen concentration per micron of nerve fiber layer thickness (O2‐C) was calculated as follows; the difference of aretrio‐venous oxygen saturation (A‐V SO2) was divided to the mean RNFL thickness. A linear mixed‐effects model was applied (IBM SPSS®)ResultsThe eyes were grouped based on their vascular responsiveness (group1 ≤ 2.90%; n = 13, group 2 > 2.90%; n = 14). In group1 and in group2, mean A‐ SO2, V–SO2 and A‐V SO2 were 96.50%(±4.38); 97.77% (±3.03) (p=0.517), 62.89% (±6.23); 60.71% (±6.28) (p = 0.391), 34.64%(±4.51); 36.68% (±5.27) (p = 0.294), respectively. Subjects in group 1 showed higher O2‐C 0.488%/µ (±0.0848) than in group2 0.434%/µ (±0.0551) (p = 0.027). Mean age (65.45 y (±11.7)) and VF(dB) defect (4.7 dB (± 3.6), 3.4 dB (±5.2) were not statistically different between groups (p = 0 > 141). In group 1, RNFL thickness was significantly less than in group 2 (72.23 µm (±12.1); 85.31 µm (±13.67) (p=0.014).ConclusionsOxygen demand was increased in patients with excessive vascular dysregulation, while mean SO2 values were not related to age and/or flicker responses. This conclusion remains to be conformed in further studies.