Oximetry in glaucoma: correlation of metabolic change with structural and functional damage

Abstract

ABSTRACT.Purpose: To determine whether retinal vessel oxygen saturation in patients with glaucoma is associated with structural optic disc and retinal nerve fibre layer (RNFL) changes and visual field (VF) defects. Methods: Fifty-nine patients with confirmed glaucoma were recruited at University Hospitals Leuven. Retinal oxygen saturation in patients with glaucoma was measured with a noninvasive spectrophotometric retinal oximeter (Oxymap ehf, Reykjavik, Iceland). VF and Heidelberg retinal tomographies (HRTs) were performed on the same day. Statistical analysis was performed using Student's t-test and Pearson's or Spearman correlation coefficient. Results: The mean oxygen saturation in venules was higher in patients with severe VF defects compared to those patients with mild VF defects (69 ± 3% versus 65 ± 6% respectively; p = 0.0003; n = 59). Accordingly, the arteriovenous (AV) difference in oxygen saturation was lower in patients with worse VF compared to those with better VF (29 ± 3% versus 33 ± 6% respectively; p = 0.002). The oxygen saturation in venules correlated with the VF mean defects (r = )0.42; p = 0.001; n = 59) as well as with the structural HRT parameters rim area and RNFL thickness (r = )0.39; p = 0.008 and r = )0.26; p = 0.05 respectively; n = 53). The AV difference decreased significantly as the VF defect worsened (r = 0.38; p = 0.003), as the rim area diminished (r = 0.29; p = 0.03) and as the RNFL thickness decreased (r = 0.27; p = 0.05). No correlation was found between the oxygen saturation in retinal arterioles and either of these parameters. Conclusion: Severe glaucomatous damage is associated with increased oxygen saturation in retinal venules and decreased AV difference in oxygen saturation. These data suggest that in eyes with severe glaucomatous damage, reduced retinal oxygen consumption is consistent with tissue loss.

Retinal Oxygen Saturation in Patients with Primary Open-angle Glaucoma Using a Non-flash Hypespectral Camera

“…These average SO 2 values are lower than those found in our study ( Table 2) and that reported previously (69% and 65% in severe and mild glaucoma, respectively). 17 However, the clinical conclusion drawn from the studies remains the same regardless of variation in average SO 2 values.…”

“…These results are in agreement with outcomes from previous studies that have investigated retinal SO 2 in patients with glaucoma using different techniques. 16,17 A complex of clinical factors contributing to the pathophysiology of glaucomatous optic neuropathy, including altered retinal blood flow and ischemia, has made the use of retinal oximetry a potentially important clinical tool in the diagnosis of glaucoma. Michelson and Scibor 10 reported significantly lower arterial oxygen saturation in patients with normal tension glaucoma (NTG) compared to healthy controls (89.7% ± 5.4% vs. 92.3% ± 3.4%) and reported a significant association with glaucomatous optic rim damage in more advanced glaucoma.…”

Retinal oxygen metabolism in healthy subjects and glaucoma patients

“…We recently reported abnormalities in retinal oxygen metabolism in patients with advanced glaucomatous visual field defects,4 and with decreasing neuroretinal rim area of the optic disc as well as nerve fibre layer thinning 5. These studies were performed with non-invasive spectrophotometric retinal oximetry6 7 and indicated increased haemoglobin oxygen saturation in retinal venules in glaucomatous eyes with advanced visual field defects compared with those with mild visual defects.…”

Reproducibility of retinal oxygen saturation in normal and treated glaucomatous eyes

“…Preliminary studies have shown impaired SaO 2 in glaucomatous eyes, especially in advanced stages, compared with normal eyes 12–14. Impaired retinal oxygen metabolism has also been associated with deeper glaucomatous VF defects,15 decreased neuroretinal rim area and RNFL thinning 16. These findings suggest that altered retinal oxygen metabolism in glaucomatous eyes may be associated with structural damage 16…”