Board Thread:Versus Debates/@comment-26388300-20160301040622/@comment-26636534-20160320155710

It blinds the target with genjutsu, it restricts the sense of sight. This would mean, blocking signals from the eyes to the brain of the target, which in the case of dojutsu users, means they can't use it. I assume this technique was created to directly counter Sharingan users.