What are some causes of sudden dog blindness?

My dog isn't that old, he is only 4. He is an American Pitbull Terrier. Lately he seems to be having trouble seeing. He can't see toys when someone is holding them right in front of his face (about 4 feet or so). He didn't recognize me coming in the door the other day. Instead of catching his ball, he has been ducking his head and avoiding it. Could I be imagining things, or is this serious? I thought I was paranoid, but my brother recognized it without me saying anything about it. I can't afford a whole lot, but if it's serious I'll do whatever I have to. Please give me suggestions.

Take this dog to your vet to examine his eyes. Lense luxation can cause this, normally seen in an older dog. Lense luxation will cause a cloudy appearance of the eyes. Poisoning can do this as well. Head injury can do this, brain tumors can do this.

Diabetes can do that - take to vet and get checked