The investigators aim to show that quantitative analysis of doppler flow velocity waveforms i.e. ultrasound which is a non−invasive and very safe means of assessing blood flow; recorded in the proximity of terminal microvascular beds of interest, (i.e. the forearm and ocular circulation) can sensitively detect and track local changes in microvascular haemodynamics i.e. the function of the small blood vessels that are found in the back of the eye and in the forearm.