This sounds very bizarre, but I have been experiencing this for probably the last few years now and I just thought to look into it. It is difficult to explain, but sometimes corners of something (like a desk, table, piece of furniture) will become very obvious in my peripheral vision to the point where it causes me some kind of discomfort and I have to cover that part of my vision. It's almost like some kind of anxiety, like I could knock my head on the corner or something, even if it's on the other side of the room from me--it's just a general feeling of "discomfort" when I am aware of said corner. I don't know if it's a physical or psychological discomfort exactly, but I believe it increases when I get tired. It may be an extension of some form of anxiety? I don't know. The "discomfort" is somewhat relieved when I look directly at the corner, but once I'm consciously aware of it, the feeling carries on and the distinctiveness of the corner within my peripheral vision isn't diminished until I either look away completely or I forget about it.