I did (and actually presently have) have an eye ailment that I am followed by a retina specialist. It is ultimately caused by excess adrenaline/cortisol that occurs during high stress. It happens more often with type A personalities and in men. I am not a man but I am type a. Some people just have a greater propensity for this to happen. Once it happens, it can happen more easily later on. which appears why my eye has it happening again. At any rate what you are talking about doesn't seem just like what happened with my vision, but this eye issue can look a bit different in people.
when it happened to me a year and a half ago, it was terrifically apparent my vision in my right eye was impaired. I went to the ophthalmologist, who saw the issue readily. I was referred to the retina guy.
again your description doesn't sound JUST like mine, except that it is all of the time.
It may very well, as slangevar suggested, be sinus related. I would probably give sinus meds a shot first. If that doesn't help, see your eye doc.
yeah NOT brain tumor though