A lazy eye is an eye that never learns to see clearly despite the fact that there is nothing physically wrong with the eye. Because the brain will not tolerate unmatched images from the two eyes, it simply tunes out or ignores one of the eyes. The end result is that an eye physically able to see is tuned out by the brain, and if left untreated until the age of eight or nine the effects will be permanent, just as though the eye is blind.