Normally a dog losing his vision will start bumping into things, or walk along the walls to get to his destination, rather than going through the middle of the room. They will might also tilt their heads more, relying more on their hearing.
I have seen the jumpy/startled reaction in more dogs who are losing their hearing.
You can also check to see if your dog can track, or follow an object, a piece of food, or a toy.
If it isn't vision there are other neurological things that could be affecting him. The nerves in the eye can have swelling and irritation too.
at 2:47 AM on Nov. 29, 2010