User blog comment:Thedrag0n22/AK-130 android visors?/@comment-9090085-20131208000243

It could be similar to the "factspheres" in Code Geass, which are normally kept almost completely covered aside from a few "eye holes" to protect them, but are fully revealed when the pilot needs to see far/wide.

So the androids keep their "eyes" uncovered while "standing watch"(so they spot intruders easily), and cover them with a visor for protection in battle(so that they're hard to "blind").

That's what I think.