Each eye is made up of six external muscles (known as the extraocular muscles). These muscles control the eye position and its movement. In a normal binocular vision, these muscles of both the eyes must be coordinated perfectly.
Certain anatomical or neurological problems can interfere with the proper functioning of the extraocular muscles, thus causing strabismus. These problems can originate in the nerves or in the muscles itself. They can also occur in the vision centers in the brain that control the binocular vision.
Strabismus can also occur due to eye injuries or general health conditions.