This paper details the development and preliminary testing of a system for 6-DOF human-machine cooperative motion using vision-based virtual fixtures for applications in retinal micro-surgery. The system makes use of a calibrated stereo imaging system to track surfaces in the environment, and simultaneously tracks a tool held by the JHU Steady-Hand Robot. As the robot is guided using force inputs from the user, a relative error between the estimated surface and the tool position is established. This error is used to generate an anisotropic stiffness matrix that in turn guides the user along the surface in both position and orientation. Preliminary results show the effectiveness of the system in guiding a user along the surface and performing different sub-tasks such as tool alignment and targeting within the resolution of the visual system.The accuracy of surface reconstruction and tool tracking obtained from stereo imaging was validated through comparison with measurements made by an infrared optical position tracking system.