Concomitant strabismus refers to the separation of the visual axes of both eyes, and the non-quality lesions of the nerve innervation of the extraocular muscles. In all directions, no matter which eye is the fixating eye, the deviation is equal. In non-concomitant strabismus, the deviation is unequal depending on the fixating eye. For example, when the affected eye is fixating, the deviation increases. Insufficient strength or paralysis of the extraocular muscles is the main cause of non-concomitant strabismus. Other causes include abnormal innervation of the extraocular muscle restriction, such as eye retraction syndrome, and A-V sign. Primary concomitant esotropia is divided into two categories: accommodative and non-accommodative. Accommodative esotropia is divided into refractive and high AC/A.