Black flashes in my eyes. help!!?

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Ive had this for a while but its become more frequent. Sometimes when iam using the computer or watching tv, my eyes will flash black for a split second as if someone turned the lights on and off. I can still see through the black though and it seems like only the outer edges of my vision flash. I have 20/20 vision although i sit in front of the computer for a large amount of time. I just want some advice first before i consult a doctor or sumthing