This is another thing I've been wondering about. I seem to have chronically dilated pupils, or they sometimes dilate all of a sudden without an apparent reason. I have no idea if it's due to mood, tiredness, general state, lighting or something else.
It's been something of a problem - I experiemented with substances several times as a teen, and my family learned about it so now they're naturally suspicious and think I'm doing drugs. It can be stressful when somebody will look me in the eye and ask me whether I'm using something. I do understand why they're doing it; they have a legitimate reason to ask. But I'm also painfully aware that the dilated pupils are apparently due to some of the problems I have, and it's no fault of mine, but I still have to apologize for it and justify myself as if I'd done something wrong. It can be really awkward and upsetting sometimes.
I'm pretty sure it has to have some connection to bipolar disorder. Dilated pupils are listed among the possible somatic symptoms, and I've talked to at least two people with the same problem and they said their pupils are usually wider than normal too. And, of course, the excitement of a manic or hypomanic state could easily cause one's pupils to widen.
But I'm curious if it could possibly have neurological causes as well. Once my oculist did recommend a neurological examination after having my eyes checked (don't remember if I told him about the dilated pupils or not), because he said the state of my eye bottom suggests neurological difference.