This may be a little bit far fetched but I also would try some Iodine in the food or drinking water. I like CS and Iodine in general for my dog because it has worked for me.
Read at the bottom of the link about the UB meridian, of course they are talking about humans but who knows it might help for dogs too. When we ever get a new dog I think I would supplement with some iodine, I keep reading how many dogs go blind and I would like to use Iodine as prevention.