by Wadih Zein, MD 

Indications: the most common indications for surgical treatment of strabismus include:

• Development or restoration of normal binocularity: near-normal alignment is a prerequisite for development of binocular vision and stereopsis. Alignment before two years of age allows the greatest chance for binocularity in children with congenital strabismus. Functional benefits of binocularity include stereopsis, expanded binocular visual fields and prevention of amblyopia. 

• Treatment of diplopia

• Restoration of normal facial appearance

• Treatment of abnormal head posture, mainly that related to an abnormality of ocular alignment

Anesthesia: despite the many advantages of local anesthesia, the majority of strabotomies are performed under general anesthesia. 

• general anesthesia is a requirement in infants and children (constituting the largest group undergoing strabismus surgery)

• intravenous propofol anesthesia may allow rapid postop recovery and thus help in planning early postoperative suture adjustment 

Surgical Techniques: the muscles can be reached through a limbal or a fornix-based approach. The four recti insertions merge into the sclera; the average insertion distances from the limbus are: 

• medial rectus 5.5mm

• inferior rectus 6.5mm

• lateral rectus 6.9mm

• superior rectus 7.7mm

The major procedures followed universally are recessions versus resections of the extraocular muscles. Recession of a muscle shortens the distance from origin to insertion and thus weakens the muscle. The muscle is disinserted and then reattached to the sclera at a recessed postion (nearer to the origin). Reattachment can be direct whereby the tendon is directly sutured to the sclera at the desired position or hangloose whence the sutures are passed through the sclera at the original insertion and the muscle is allowed to "hang" from them at the desired position. Resections of the recti effectively shorten the muscles and thus increase the amount of tension produced and strengthening the muscle. The technique involves resecting part of the muscle and then reattaching the rest to the sclera usually at the original insertion. Whether performing resections or recessions, good measurements are a prerequisite for the success of the operation. In addition, the surgeon needs to follow general rules in the amount of resection / recession done. For the horizontal rectus muscles, about 2-3 prism diopters of correction are expected per mm of surgical correction. However, the results are not exact and can vary with the age of the patient, the size of the globe, and the degree of recession / resection. Different combinations of surgical procedures can be applied eg. in esotropia the  patient can undergo bilateral recessions of the medial recti or a unilateral recession of the medial and resection of the lateral rectus to achieve similar results. Other variations include the use of adjustable sutures whereby postoperative adjustment of the suture knots allows excellent alignment. This technique is most helpful for patients with whom the surgical response may be unpredictable or in diplopic patients in whom exact alignment is necessary. Strabismus surgery also includes transposition surgeries where some muscles are used to make up for the paralysis or paresis of other muscles; furthermore, multiple oblique muscle procedures can be done but are beyond the scope of this text.

Complications: Undercorrection  and overcorrection are probably the most common "complications" noted following strabismus surgery. Many of these are transient and can be corrected by optical means (prisms, lenses), others require surgical correction for cure. Other complications include:

• Perforation of the sclera

• Lost and slipped muscles 

• Infection

• Anterior segment ischemia: Much of the anterior segment circulation derives from ciliary arteries which are affected by surgery involving the extraocular muscles. This occasionally leads to a peculiar complication called anterior segment ischemia manifesting with a significant anterior chamber reaction, iris atrophy, and various degrees of cataract formation. Its occurrence following strabismus surgery is correlated with the number of operated muscles and the general circulation characteristics of the patient.

• Postoperative diplopia

• Conjunctival granulomas and cysts