Eye Flashes

i've been having flashes mainly in the right eye for 6+ years, sometimes once a month, sometimes once or twice a week. It lasts anywhere from a few seconds to several minutes. A lot of times it seems to happen when I've been working on the computer a long time or watching tv. My eyes are also sensitive to bright lights. i'm anxiety prone and freaks me out, so really would like to find out what causes it. I've heard that high blood pressure can cause, retinal pulling and headaches. I've been to my opthamologist several times and says all is well, other than my eye pressure being in the higher 'normal' range. Please help!