In this paper, both implantable subretinal prosthetic systems and closed-loop epileptic seizure control systems reported in the literature are analyzed and reviewed in the terms of chip design, integration, and animal tests. In the review of subretinal prosthetic systems, the four main parts, image sensing, stimulation, data/power transfer, and implantation, are investigated and compared. The review is followed by a comparison to provide a summary. The future challenges and the development of bio-subretinal chips with retinal cells grown on chips are also presented. In the review of state-of-the-art papers on closed-loop epileptic seizure control systems and system on chips (SoCs), the four main parts, the neural-signal amplifier, biosignal processor, stimulator, and wireless telemetry, are investigated with the design requirements and advantages/shortcomings. The review is summarized by a performance comparison table. It can be seen that the closed-loop epileptic-seizure-control SoCs have advanced to clinical applications on humans. Both reviewed implantable systems will be important milestones for future bioelectronic medicine.