This paper proposes a novel energy-efficient approach dedicated to high-density implantable stimulators such as visual prostheses. Energy efficiency of the approach proposed in this work is achieved through two ideas: the `tracking supply ribbon' technique, and `reverse charge pumping'. The proposed approach is implemented, in the multichannel case, in such a way that power efficiency of each stimulation channel is enhanced according to its specific voltage/current condition and independently from other channels. Based on the proposed approach, a 16-channel stimulation backend for a visual prosthesis was designed and simulated in the transistor level in a low-voltage 0.18μm triple-well CMOS technology, occupying 1 mm2 of silicon area. According to post-layout simulation results, power savings of up to 74.9% are achieved compared to the conventional output stage with a constant supply voltage.