This just happened to me. I just started working at a help desk for about a week using a computer all day long. On Sunday I was using MS Flight simulator X for about 2 hours when my left eye had had trouble reading text. I went to eat dinner and the bottom of the corner of my left eye started jumping and flashing. I went to bed right away to rest my eye. This never happended to me before. I believe it was too much time on the PC, old age or eyestrain. I am 60. I used to wear contacts but now I wear bifocals. I need to spend less time on the PC which is hard when I have to use it every day at work. I will use it less at night.