Strabismus, also known as crossed eyes or lazy eye, is a condition in which the eyes are not properly aligned with each other and point in different directions. The main cause of strabismus is an imbalance of the extraocular muscles that control the movement of the eyes. This imbalance can be caused by a number of factors, such as a birth defect, an injury, or a neurological disorder. In some cases, strabismus can also be caused by a refractive error, such as nearsightedness or farsightedness.