Scar remodeling after strabismus surgery

Patients with overcorrected strabismus (and several patients with undercorrection after extraocular muscle resection) underwent exploration of previously operated muscles, with the intention of advancing their tendons to prevent the need for surgery on additional muscles. Unexpectedly, it was found that, in many cases, an elongated scar segment of variable length was interposed between the muscle and its insertion site on the sclera. Laboratory investigations were carried out to elucidate the underlying mechanism(s) and to create an animal model of the disorder.

Lengthened scars were repaired on 198 muscles during 134 procedures performed on 123 patients. The scars consisted of amorphous connective tissue interposed between the globe and normal tendon. Repair was accomplished by excision of the scar and reattachment of the muscle to sclera, using absorbable sutures in 64 cases and nonabsorbable sutures in 70 cases. Histopathologic examination was performed on 82 clinical specimens, and tissue culture studies were performed on 7 specimens. To develop an animal model, 10 New Zealand white rabbits underwent bilateral superior rectus resection. Half of the eyes received sub-Tenon's injections of collagenase over the operative site during weeks 2, 3, 5, and 6 postoperatively; the other half received saline solution injections on the same schedule. At 10 weeks, half the sites were studied histologically, and the other half underwent collagen creep analysis. In a second study, the use of absorbable versus nonabsorbable sutures was compared in the rabbit model.

In the clinical cases, the mean length of the elongated scar segments was 4.2 mm. A total of 105 of the 134 repair procedures were judged successful. Thirty-one procedures resulted in recurrence of the original overcorrection; 7 of these had documented restretches. Factors that distinguished patients with stretched scars from patients with classic slipped muscles included minimal or no limitation of versions, less separation of the tendons from sclera, and thicker appearance of the scar segments. The use of nonabsorbable sutures in the repair procedure reduced the recurrence rate. Histologic examination of the clinical stretched scar specimens showed dense connective tissue that was less well organized compared with normal tendon. In the tissue culture studies, cells cultured from the stretched scar specimens grew rapidly and were irregularly shaped. A high-molecular-weight protein was identified in the culture medium. By contrast, cells cultured from normal tendon (controls) grew more slowly and regularly, stopped growing at 4 days, and produced less total protein than cultured stretched scar specimens. In the animal model studies, the collagenase-treated sites showed elongated scars with increased collagen between the muscle and the sclera, as well as increased collagen creep rates, compared with the saline-treated controls. The use of nonabsorbable sutures in collagenase-treated animal model surgery sites was associated with shorter, thicker scars compared with similar sites sutured with absorbable sutures.

A lengthened or stretched, remodeled scar between an operated muscle tendon and sclera is a common occurrence and is a factor contributing to the variability of outcome after strabismus repair, even years later. This abnormality may be revealed by careful exploration of previously operated muscles. Definitive repair requires firm reattachment of tendon to sclera with nonabsorbable suture support.