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Editors Selection IGR 8-4

Bloodflow: Flicker

Comment by Alon Harris on:

15133 Chorioretinal vascular oxygen tension changes in response to light flicker, Shakoor A; Blair NP; Mori M et al., Investigative Ophthalmology and Visual Science, 2006; 47: 4962-4965

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Many prospective clinical investigations have found reduced ocular blood flow to be implicated in the pathophysiology of glaucomatous optic neuropathy. Although imaging of the ocular vasculature is possible with various technologies, blood flow remains a surrogate for ocular metabolism and oxygenation.

Shakoor et al. (1137) have attempted to record oxygen tension in the retinal and choroidal vasculature of the rat eye during visual light flicker stimulation. The authors found retinal arterial PO₂ and arteriovenous PO₂ differences increased with increasing light flicker at frequencies up to 10Hz while retinal arterial PO₂ decreased significantly with increased distance from the optic nerve head, whereas retinal venous PO₂ remained relatively unchanged. The authors provide an excellent imaging method which provides assessment of the partial pressure of oxygen in arteries, veins and capillaries of the retina and choriod. It is unfortunate, however, that the technique is limited to an animal model due to the toxicity of the phosphorescent probe. The methodology of the probe also moves the model away from normal physiological conditions within the tissue tested. This limits applicability of these results in humans. Another limitation exists as the authors do not provide any statistical power calculations regarding their sample size and procedures. The authors correctly point out that changes in the tissue oxygenation must be interpreted in relation to ocular vasculature to advance the understanding of oxygen dynamics in challenged physiological states such as glaucoma. Reliable devices capable of determining oxygen content within human eye tissues remain somewhat elusive but vital to pursue.

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