In ophthalmology, convergence is the simultaneous inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision when viewing an object. This is the only eye movement that is not conjugate, but instead adducts the eye. Convergence is one of three processes an eye does to properly focus an image on the retina. In each eye, the visual axis will point towards the object of interest in order to focus it on the fovea. This action is mediated by the medial rectus muscle, which is innervated by Cranial nerve III. It is a type of vergence eye movement and is done by extrinsic muscles. Diplopia, commonly referred to as double vision, can result if one of the eye's extrinsic muscles are weaker than the other. This results because the object being seen gets projected to different parts of the eye's retina, causing the brain to see two images.