Cannulation of small retinal vessels is often prohibitively difficult for surgeons, since physiological tremor often exceeds the narrow diameter of the vessel (40-120 microm). Using an active handheld micromanipulator, we introduce an image-guided robotic system that reduces tremor and provides smooth, scaled motion during the procedure. The micromanipulator assists the surgeon during the approach, puncture, and injection stages of the procedure by tracking the pipette and anatomy viewed under the microscope. In experiments performed ex vivo by an experienced retinal surgeon on 40-60 microm vessels in porcine eyes, the success rate was 29% (2/7) without the aid of the system and 63% (5/8) with the aid of the system.