For About A Week, I Have Noticed A Flicker Of

For about a week, I have noticed a flicker of light on the very outer edge of my right eye. I also have a spot off center to the right of looking straight ahead. The spot won't go away. I walked out to the garage to take the trash out (it is getting dark out) and didn't have my glasses on and I saw the flicker again. When I move my eyes quickly toward the flicker of light it goes away. But if I look quickly to my right I can make it come back over and over. What is this? I had breast cancer 10 years ago. Double mastectomy. I am "remarkably" healthy as doctors put it! I've never smoked and don't drink or do drugs.