From pedigree.com
"There are many reasons a dog may go blind: infection, hereditary disease or just old age. For some dogs the blindness will be a gradual thing, although sudden blindness can occur as a result of a traumatic experience, such as a car accident. If a dog goes blind gradually, by losing sight in one eye and then the other, an owner might not even notice until the day they move the furniture and the dog starts walking into things. This is a common occurrence that many owners punish themselves for; they think they should have recognized the problem the first time their dog ran past them or bumped into a doorframe. Most of the time it’s not until you start adding up your dog’s strange behavior that you realize there is something wrong."
