I Suddenly Noticed What Appeared To Be A Multi Faceted

I suddenly noticed what appeared to be a multi faceted crystal in the near center of my field of vision. Over the next few minutes the crystal structure moved to the right and seemed to spread out till it reached the far right side of my vision. Did not see it when my eyes were closed but saw the same thing with one eye closed, first my left and then my right. The episode lasted about 20 - 30 minutes. It is gone now. This seems to not be an eye problem but a symptom of another problem that affects that effects bot eyes or vision. I am 72 years old. Any suggestions.