You should definately take him or her to the veterinarian, if the pupil (the circle in the middle) is the part that's turning white.
My Dog Eye Is Turning White What Do I Do?
My neighbors dog has a white eye.they said thats was a sign that he was turning bling so they took him to a vet and they said his eye could leave him to a siries sickness and problems.
Take him/her to the pond so they can see whats wrong with you dog