**3. Surgical indication and planning for success**

The indications for strabismus surgery fall into two categories: binocular function and cosmetic appearance with psychosocial impact. The indication and surgical goal should be based on the patients need prior to surgery and direct the surgical plan in order to achieve a successful result. Therefore, prior to surgery, the strabismus surgeon needs to establish the treatment goals by asking "Why are we operating"? Is it to establish binocular fusion, eliminate diplopia, expand the field of binocular vision, correct a compensatory head position, or improve cosmetic appearance?

Signs of binocular fusion potential include intermittent strabismus, acquired strabismus, binocular fusion after neutralizing the deviation with prisms, child <2 years old, equal vision, and incomitant strabismus with compensatory face turn. Patients with fusion potential generally require large amounts of surgery, larger than standard surgical numbers to avoid undercorrection. However, in patients without binocular fusion, it is better to do less surgery, as a small residual esotropia is more stable and cosmetic acceptable than a consecutive exotropia.

Furthermore, defining the whished function outcome influences the selection of type of surgery. Monocular recession–resection surgery results in incomitance, which is not preferable in a fusing patient, as incomitance can cause diplopia in eccentric positions of gaze. Monocular surgery, however, is the procedure of choice for sensory strabismus to protect the seeing eye.

A specific strabismus diagnosis should be established preoperatively, and the exact etiology of the strabismus should be determined, if impossible, by an MRI of the head and orbit may be indicated. If the cause is unknown after a complete work up, then it is appropriate to operate for the strabismus taking into account the ductions, versions, and presence of incomitance.

Each patient requires an individual surgical approach to the management of their strabismus, but the following information and measurements may be of assistance as a guide for how much muscle surgery is required for concomitant deviations without previous surgery or underlying muscle or neurological pathology, particularly for those beginning strabismus surgery.
