Story takes place in an urban environment, the character spends most of his time indoors. He suffers from chronic miosis, aka persistently contracted pupils. I'm not entirely sure why he does, I'm still thinking about it, but as far as I know he doesn't have any specific diseases causing it. He is not on any drugs of any kind. If it is connected to some kind of condition, it is probably a congenital condition or caused by a disease he got early in life. I don't know if it can be caused by any sort of "it just is that way, man" kinds of things, like a problem with the muscles that control the dilation of the pupils, but if that is possible than that is what it is, because I'm only trying to deal with this one symptom.
I'm trying to determine whether or not miosis that is not caused by extreme light - this guy's pupils are contracted even in the dark; no matter where he is they are tiny little pinpricks - has any effect on your eyesight. As in, if your pupils are constantly too small, how much can you see in the dark? In normal light? Etc. I've looked up "chronic miosis," "pupils," "does ___ have any effect on ____", and a few similar phrases, but nothing turned up. I looked on Wikipedia as well as a few medical websites. I've found that having consistently dilated pupils has an effect in both light and darkness, so I'm assuming there is an effect, but I do not know what it is.