Abstract: Aspects of this disclosure are directed to optical probes for collecting images of a region of interest for determining wall shear stress. The optical probe includes an imager with a line of sight and a light guide configured to steer light from a light source to the region of interest. The optical probe includes an objective configured to focus light reflected off of the region of interest to the line of sight of the imager. The optical probe can include a micro-lens array at the objective. The micro-lens array can focus light from the objective onto the imager. The imager can collect images from the light from the micro-lens array for determining wall shear stress at the region of interest.