I think the visual symptom that HPPD, PMA (persistent migraine aura), and VISUAL SNOW is pretty the same but the exact mechanism that triggers it isn't known yet. I have VISUAL SNOW 24/7 since I remember and I've never never smoked or taken any drugs. There are about 400 people on FB - group VISUAL SNOW who share this condition, someone since they were young others later, that are trying to create awareness to this condition that many doctors actually don't know the existence and they are unable to manage. I partecipated this year to the study of the dr Schankin and I can assure you it was the first time after 35 years one person knew what I was talking about. So I wanted to clarify more this point.
Probably this is the reason why dr Abraham talked about a genetic condition which is triggered by drugs.