The co-movement of both eyes is coordinated by the lateral visual center and the medial longitudinal bundle. One-and-a-half syndrome is caused by a lesion in the pontine perisylvian region, which causes simultaneous effects on the pontine lateral visual center and the medial longitudinal bundle, mainly manifesting as a lesion of the eye. As the name implies, one-and-a-half syndrome means that one and a half eyes are immobile, which is manifested by the fact that the affected eye is fixed and cannot be either adducted or abducted, while the eye on the other side can be abducted but not adducted. The common causes of one-and-a-half syndrome are mainly in the brainstem, such as hemorrhage, infarction and multiple sclerosis of the brainstem, etc. Different treatment plans are needed for different causes.