We present a two-dimensional, vision-based force sensor, capable of sensing μN level forces. There are currently no reliable, off-the-shelf, commercially-available force sensors to measure forces at this scale, that can be easily integrated into standard microrobotic test-beds. Our design consists of a planar, elastic mechanism with known force-deflection characteristics. A CCD camera is used to track the deformation of the mechanism as it is used to manipulate objects in a micro/mesoscale robotic manipulation test-bed. By observing the displacements of select points in the mechanism, the manipulation forces can be estimated. The modeling, design, microfabrication, calibration and experimental validation of the force sensor are presented with a brief discussion of an application to a robotic manipulation tasks such as microassembly.