In my reading most reports of HPPD are actually reports of acute persistent visuals after tripping - which a lot of people don't realise is a normal thing, particularly with phenethylamines. If I take a phenethylamine it's 4-5 days from a single dose where I'll have visual alterations occur rarely throughout the day, and much longer if I'm dosing with any sort of consistency.
I've spoken to so many people who claim to have HPPD who haven't been even a month without taking a psychedelic in many years and suspect that most "HPPD" cases are not HPPD but just these acute persistent visuals which are to be expected if you use psychedelics, they go away after a break from all drugs for a few months in most instances.
Real HPPD is when it doesn't go away even if you were to abstain for years from all drugs.
Also some cases of "HPPD" may actually be visual problems people are experiencing for reasons other than drugs but that may be worsened by drug use - visual static/visual snow is a common example, empathogens and stimulants and phenethylamine psychedelics seem to be the major causes for making it worse in my experience at least as someone who has had visual static/snow since a kid. The worsening seems to be temporary though and tryptamines have an opposite effect, reducing my visual snow temporarily - the visual snow also drops to an almost unnoticeable level if I take no empathogen/psychedelic/stimulant for a few weeks. Another example is Posterior vitreous detachment which can produce weird fractal like sparkles inside your vision at random times (or 24/7) until you force yourself to ignore it:
http://en.wikipedia.org/wiki/Posterior_vitreous_detachment I also have this in my left eye and initially thought it was HPPD until I saw an eye doctor.