• colour Doppler imaging
• blood flow
• humans

Efforts to analyse the complex vasculature of the eye have been frustrating to say the least. We still must rely very much on fluorescein angiography. Laser Doppler flowmetry has not yet yielded the results that had been hoped for. The same has been true of colour Doppler imaging. In a recent attempt on my part to make sense of many techniques used to study the circulation of the optic nerve, my conclusion was that much work still needs to be done.¹ Harris and colleagues are to be commended for relentlessly struggling to find better ways to determine how blood flow can change under a variety of clinical settings using several techniques, especially colour Doppler imaging.

Until recently, colour Doppler imaging has been limited to visualising blood vessels, identifying direction of blood flow, and calculating blood velocity only. Pulsatility and resistive indices provide indirect evidence of resistance at or nearby the ultrasound probe, but volumetric blood flow (amount of blood/time) has not been measurable. The main problem with accurately assessing the orbital vessels has …