When people ask me how on Earth I decided to be an eye doctor I have to admit my father was one. I had never intended to do what he did and I thought I had ignored all his advice. When he told me that ‘observational’ (a.k.a. ‘Phase 4’ or ‘post-marketing’) studies were needed to show that treatments identified by randomised clinical trials (RCTs) actually worked in routine clinical practice, I thought he was just trying to boost his publication list. It turns out that I was wrong about that too.