Flashing shadows in vision, happens when getting Migraine, things are hard to focus. Solution?

I have been experiencing some flashing shadows in my vision . Usually I have noticed them when I get a migraine-I get them real bad. Lately I have gotten them when I dont have a headache of any kind. They are not painful other than when they are with a HA. I can see through them, but things are sometimes hard to focus on through the shadows. They pulse with my heartbeat-(I can see my heartbeat in the shadows) I dont know what triggers them, they are more prevelent when in a well lit area or looking into light like at computer or bright room.