The in vivo measure of the retinal blood flow is very important to diagnose ocular diseases. The blood velocity can be derived from laser Doppler velocimetry. A measure of the local diameter of the vessels would allow estimating the retinal blood flow. The response of steered Hessian wavelets may constitute an accurate method to estimate localized vessel diameters, where the diameter is expected to be proportional to linear combinations of the local maximum steered response of multi-scale Hessian filters. Basic knowledge in image processing and Matlab or Java will be helpful.