By definition, strabismus is a condition in which there is a deviation of one of the ocular axes with regard to the other. It can be convergent (towards the inside), divergent (towards the outside), or more rarely vertical or torsional.

Some kinds of strabismus can be partially or completely corrected with surgery. The best time to perform the surgery depends on the specific kind of strabismus, whether there are other visual abnormalities and also of the age of the patient.

The strabismus surgery can have different aims: the improvement of the visual function (for example the stereoscopic vision in children); a suppression of double vision (for example in the case of strabismus acquired in adult age); and in certain cases an aesthetic correction.

The amplitude of the surgical correction is based on the measurements of the deviation of the ocular axes in all directions of the gaze. These are done with the aid of prims during the pre-operative assessment.

The surgery consists of weakening (by recoil) or strengthening (by folding or shortening) one or some of the six ocular muscles around the eye, the extra ocular muscles. It is performed under general anaesthesia and it lasts about one to two hours, depending on the number of muscles to be operated.