"There are a lot of different vascular beds in glaucoma," he explained, speaking at the January meeting of the Contact Lens Association of Ophthalmology in Las Vegas. "And when we talk about blood flow, we aren’t talking about anything in particular. We have to be more specific and define what we’re talking about.

"Changes in blood flow in one area may signal an improvement but may be a negative for another area, creating a steal phenomenon.

"So even though we have measures of improved blood flow, say, by one technique in one vascular bed, it doesn’t mean that this is necessarily good for the eye," he continued. "And that is part of the problem with the blood flow area right now – that is, defining where it is within the eye that blood flow abnormalities are important. Or what combination of abnormalities (are important), or what’s the overall picture with regard to ocular blood flow and how do we measure it?"

Currently, he said, researchers are working with Doppler imaging, retinal flow meters, scanning lasers and high resolution angiography. But no existing technology encompasses all possible methods of measurement.