My Sugar was blind w/ cataracts when we adopted her; she has since had surgery, and new lens implants, both eyes.

This is what the eye specialist did to determine how much sight she had:

Dog up on the exam table (you could use the kitchen counter).
First, drop a cotton ball -- you want something with NO smell, and NO noise when it lands. Hold it dog's muzzle gently, so she can't move her head, and drop the ball first on the right, then on the left. So, you are testing each eye.

Next, do the same with a Q-tip.

If the dog tracks the item, then she sees it.

Hope that helps!