Ludwig and Chow introduced the entity of stretched scar as a separate entity in the domain of secondary strabismus11. In the stretched scar-induced strabismus, secondary deviations occur months to years after the primary procedure, in contrast to the slipped muscle, in which the secondary strabismus occurs in the immediate postoperative period12. This case series shows clinical characteristics and results of management of secondary strabismus caused by stretched scar. Overall, stretched scar-induced secondary strabismus should be suspected in cases with late over or undercorrections associated with limited duction of the previously operated muscle. Management which includes exploration, excision of the scar tissue and reattachment of the muscle to the sclera using non-absorbable sutures is usually effective in restoration of normal muscle function. However, additional surgery of antagonist muscles might be needed in selected cases.
In this case series, the average interval elapsed between the primary procedure and correction of stretched scar induced strabismus was 7.7 months (range; 2–36), a significantly smaller interval when compared with 10, 13 and 29 years that were reported in previous trials11, 14, 15. The long-time interval reported in the previous trials could result from the relative non-familiarity of the issue of stretched scar as a cause of residual or consecutive strabismus.
The issue of the stretched scar was addressed in few previous reports. Most of those reports dealt with the stretched scar as a cause of consecutive exotropia following recession of both medial recti for the treatment of esotropia. In one case series, which addressed stretched scar-induce consecutive XT; mean XT was corrected from 33.1PD to 12PD after 4months of scar excision combined with single medial rectus muscle advancement using absorbable sutures15. In the consecutive XT subgroup of the current series (3 cases), mean angle of deviation was improved from 38.4 PD XT to 14.3PD ET after combined excision of the scar tissue and MR advancement.
In the past, the underlying pathophysiology responsible for the development of late secondary strabismus associated with weak ocular duction was poorly understood. This had led Cooper16 to suggest treating cases of secondary strabismus by operating on the fresh muscles instead of the previously operated ones. However, it was until the observations of Ludwig and Chaw which identified the stretched scar as the culprit for cases of late secondary strabismus associated with poor extraocular muscle action, and also differentiated it from the previously well known “slipped muscle”.
Despite its retrospective nature, small sample size and short follow-up, this trial agrees with the work of Ludwig and Chaw in that the stretched scar should be suspected in any case of overcorrection (following previous recessions) and undercorrections (after previous resections) accompanied with any degree of poor muscle duction. Key factors in diagnosis of stretched scar are the late onset and the slowly progressive course of late deviations associated with variable degrees of weakness of ocular duction. Intraoperative forced duction test, which is usually negative in these cases, is used to differentiate stretched scar from tightness and stricture of the antagonist muscle especially if unilateral recess-resect was the primary procedure.
In the current trial, management of stretched scar yielded satisfactory results. Significant correction of ocular deviation, improvement of diplopia and improvement of limited ocular duction has been observed following excision of the scar tissue with muscle attachment to the sclera using non-absorbable sutures. In general, excision of the scar tissue accompanied by variable degrees of muscle advancement was usually effective in control of consecutive deviations where the involved muscles were previously recessed while in recurrent deviations, where the involved muscles were previously resected, additional surgery on antagonist muscles was sometimes required.