A man with one eye is not half blind.
His peripheral vision on one side is diminished, and he lacks binocular vision, but other than that he sees as well as any two-eyed person. The former is solved by turning his head, and the latter is overrated because it’s useless beyond about fifty feet, so I have my doubts about the supposition as to why we have two eyes. I suspect it’s not about judging distance, it’s for the same reason that submarines have two air compressors (and we have two kidneys, come to think of it); it’s in case one of them fails.
Vision does not happen in the eyes, it happens in the brain. Eyes merely provide signals to the brain and the brain builds a picture based on the data available to it. It does not care whether the data came from one eye or from two. When it comes from two eyes the brain feels no compulsion to average the input from both eyes, it discriminates in order to build the best picture. If one eye is providing bad data, the brain has no compunction whatever in discarding that data.
This profound insight occurs to me because right now one of my eyes is providing good data and one is providing bad data, but my vision is astonishingly clear and sharp. You may be wondering how that came to be, but even if you are not I’m going to tell you.
Over the years my eyes have been developing cataracts. Nothing unusual about that, but mine had become really bad, and my vision was terrible. I knew I could not drive a car at night, but in truth I probably should not have been driving at all. (Sorry.) When watching a football game, I inferred by the actions of the players where the football was, because I never actually saw the ball.
Then I had the cataract removed from one eye. It healed immediately, as they are wont to do, and my vision did not improve halfway, it was cured. (I’m having the other eye done this week nonetheless.) I’m watching the LSU/SC game and, “Oh look, there’s the football, right there on the ground.”
So having my vision restored is awesome, of course, and was why I had the procedure, but there was a nice little lagniappe of getting a real life lesson in how the brain works. And it proves, notwithstanding my wife's assertion to the contrary, that I have a brain.
Update, Wed 5:30pm: In all fairness to my wife, she has never actually asserted that I have no brain. She has merely suggested that my actions at times might indicate that said organ was underdeveloped or possibly altogether missing.