Double vision (diplopia) is seeing two images of one object. In order for the brain to receive a clear image, both eyes must move in unison. This condition may result from weakness in one or more of the muscles that control eye movements. When this happens, the good eye focuses on a seen object, but the affected eye is focused elsewhere. Other causes include fatigue, alcohol intoxication, multiple sclerosis, or trauma. The sudden and ongoing appearance of double vision may indicate a serious disorder of the brain or nervous system.