Glaucoma is associated with reduced ocular blood flow and changes in retinal vascular oxygen saturation. To fully understand alterations in oxygen metabolism associated with the disease concomitant measurements of blood flow and oxygen saturation are required. This is the approach taken by Aref and co-workers who measured total retinal blood flow using Doppler Optical Coherence Tomography (OCT) and oxygen saturation using a dual wavelength Scanning Laser Ophthalmoscope (SLO) in a small group of patients with primary open angle glaucoma (20 eyes of 14 patients). The authors showed that increasing glaucomatous visual field loss was associated with reduced total retinal blood flow and reduced oxygen delivery.
There is a long-standing discussion whether changes in blood flow and oxygen metabolism are primary or secondary in glaucoma. Since this small-scale study was cross-sectional it does not contribute to the solution of this fundamental question
The strength of the study is related to the use of sophisticated technology that allows for quantitative assessment of oxygen metabolism. Limitations are the small sample size and the lack of a control group, which would be required to understand the potential of the technique in discriminating healthy from diseased eyes. There is a long-standing discussion whether changes in blood flow and oxygen metabolism are primary or secondary in glaucoma. Since this small-scale study was cross-sectional it does not contribute to the solution of this fundamental question. Do the techniques used by the authors have potential to be established as a diagnostic tool in glaucoma? Most likely not, because they do not provide localized tissue oxygenation. Technologies that do provide high lateral resolution for quantification of tissue oxygen may, however, be promising because they could identify areas of reduced metabolic demand due to neural loss.