Of course it's my no means a simple task, especially that an implant also needs to be unobtrusive. Especially retinal implants, as they're on the border of nanotechnology. A full ocular implant could probably afford to take up more space, but still would have to be stuffed into an incredibly small space. I believe such a small camera could be made, though, and a basic image processing system itself could probably fit, too. Still, there's the problem of interface, and another of powering and cooling the thing. Real-time, hi-res image processing is expensive, performance wise, and while a modern, dedicated subsystem could probably accomplish that, it's power drain and heat output are gonna be on-par with a gaming-grade GPU.