I think I know what you mean. For most people, I think it has to do with the eye suddenly being exposed to much brighter light (like watching TV for an hour, then going and looking out the window) and the pupil overreacts and shrinks.
But sometimes it just happens... with no real apparent reason, and it's like I can see maybe a square inch from about 2 feet away and the rest is all black and it lasts about 15 -30 seconds.
But sometimes it just happens... with no real apparent reason, and it's like I can see maybe a square inch from about 2 feet away and the rest is all black and it lasts about 15 -30 seconds.