Yep, your vet was absolutely correct. Can take a few months to see a change if it is a vitamin A issue.That's exactly what we are doing. Our vet said the same. He said he would rather try to increase the Vitamin A this way, so we can rule it out (of course, it's always on the list of possibilities for chams) than do injections or liquid which could cause overdose.
Just a light dusting.This course will take a little longer to see a benefit he said, be he's being cautious, which I appreciate.