The first definition is from the Oxford Dictionary of English, the second from the Online Medical Dictionary.

The difference between the two suggests there might be a technical usage and a pedestrian usage. Such as, "For Pisser Burke the skirl of bagpipes evoked an eidetic mental picture of the Lowlands", or "Subject A suffered from diminished eidetic memory retention"

It says the word was coined. It would be helpful to know who coined it and why.