This paper describes the development and results of initial testing of a cooperative robot assistant for retinal microsurgery. In the cooperative control paradigm, the surgeon and the robot share control of a tool attached to the robot through a force sensor. The system senses forces exerted by the operator on the tool and uses this information in various control modes to provide smooth, tremor-free, precise positional control and force scaling. The robot manipulator is specifically designed with retinal microsurgery in mind, having high efficacy, flexibility and ergonomics while meeting the accuracy and safety requirements of microsurgery. We have tested this robot on a biological model and we report the results for reliably cannulating approximately 80 microm diameter veins (equivalent in size to human retinal veins). We also describe improvements to the robot and the experimental setup facilitating more advanced set of experiments.