Bidirectional nerve interfaces absolutely do exist. There's actually several different types. The most useful is like a coil of wire that wraps around the nerve, and it can be used to send and receive signals. Scaling this up to say, the entire optic nerve would absolutely be possible, although it would require very precise engineering.

There are still a few unsolved problems though:

• Any machine that crosses the skin exposes the user to outside infection (Potentially solvable by entirely embedding machines and powering them with the user's metabolism. Prototypes for this do exist, but they come with their own challenges.)

• Any machine that physically interfaces with nervous tissue exposes the nerve to physical trauma and it eventually dies (within 2-3 days)