I usually put fly mask on just for the day, however my paint (with sensitive skin) was bitten by flies (bee?) in face to the point of having a big wound.
I put medication on her twice/day, and mask for the day, unfortunately by the time we get to the field in a morning there are already flies there hunting for her sore. So I was thinking about just keeping mask on 24/7 for some time. My concern is can they still see in dark with that mask on?