content: What happens when there's a new model out?  Your eye explodes from sheer redundancy, happens all the time with phones and replacement limbs.  What happens if they're hacked (possible on a large scale), security on these things is generally terrible.  You might have to remove or turn it off to disable whatever nonsense is being displayed, of if the hardware is targeted you might need to get a replacement.  What happens if someone used an EMP, or there's a thunder stoem in the future if lots of people had similar implants?  Then it will stop working, like all other unshielded electronics.