Explained: To prevent double vision, the brain exploits a feedback system, which it uses to finely tune the lengths of the muscles controlling the eyes. This produces phenomenally precise eye movements, Guyton said. Each eye has six muscles regulating its movement in different directions, and each one of those muscles must be triggered simultaneously in both eyes for them to move in unison, according to a 2005 review in the Canadian Medical Association Journal. “It’s actually quite amazing when you think about it,” Guyton told Live Science. Bemjamin Plackett, “Why eyes move together” at LiveScience Hat tip: Philip Cunningham