I've never has a problem with Vit A deficiency. Are you feeding a good variety of greens and veggies? A good UVB light? UVB lights decay and some can be defective so it could be worth it to replace the bulb your using. The twisty style compact florescent lights are completely useless.. Mercury vapor bulbs are my preference but the long tubes hold up well.. But they have a somewhat limited distance for proper exposure.
Try some repashy superVeggie dust. I use it for my Uromastyx but not my iguanas. I do not use supplements as a crutch like many do (including breeders) but if there is a deficiency it comes in handy - its a good formula for herbivores. As with every sort of supplement you only need a pinch or 2 of it and only feed every few days. You will probably have to google search to purchase this stuff I do not believe local stores will have it. I know deerfernfarms.com stock it.