That's the problem with studying animals, they can't defend themselves to correct our hilarious over-generalizations and misrepresentations of their species.

I did a little research on how they determine the visual acuity of dogs. Apparently it is done by training the dog to respond to lines on a background in order to receive a treat. Once the lines become so small that the dog no longer responds they have arrived at their answer.

What strikes me as odd is that they have taken a test designed for humans and modified it to be used for dogs. One issue with this is the fact that when a person takes a vision test they are trying very hard to discern the correct letter. Anybody who has gone thorough one of these tests will know what I am talking about. At some point you get to a letter size where you will spend considerable effort scrutinizing it. Is it a 'C' or a 'G'?

It seems to me that you should probably design a test for dogs that brings out a similar level of effort.