First of all, I'm not a vet - I'm simply trying to help.
It's difficult to give advice without seeing the dog's eye or a photograph of it, but it sounds like your dog may have an eccentric pupil. This is where the pupil has failed to center in the iris and gives the impression of a blue spot on the eye.
Alternatively, your dog may have a cataract which is a clouding of the eye, giving the appearance of paleness on the pupil.
Try looking these up on the internet and judging for yourself.
