So the way I see this is it is essentially the difference between fluff and crunch. Fluff is just how things appear, but essentially has no impact on the game or how it's played. For example, let's you wanna play a Bridge Troll afflicted with dwarfism. Obviously there's no race or subrace for players to play a troll, let alone a diminutive one. But you can use the stats of a Gnome or Halfling and just call yourself and act like a Bridge Troll with Dwarfism. This has no effect on the game play, as you are essentially just re-skinning existing rules.
I once played a human monk that was 90 years old. There's no way a 90 year old could move like a monk does. But the fact that my character was 90 had no impact on the game mechanics. It didn't benefit my character mechanically. Just because I wanna play Master Roshi, doesn't mean I have to impose penalties to my physical stats. What is this, 2nd or 3rd edition?
Anyways, I would personally say that as long as what you use doesn't give you any mechanical advantage beyond what functioning eyes would provide, it doesn't matter if you wanna claim it's a sonar collar (Like Broadway in the apocalyptic future episode of Gargoyles), if you have seeing-eye sprites, or need to hold a crystal ball up to your forehead. Once you start claiming that you should get advantage on perception rolls for hearing (the sonar collar option), can use your sprites to see around a corner for you, or the crystal ball allows you to see invisible creatures or through illusions, then you are getting into areas that DO require mechanical tweaking to ensure those options are balanced against what the other players in the game can do.
