Theoretical effects of surgery on length tension relationships in extraocular muscles.

The main effect of recession or resection of a rectus muscle is thought to be due to an alteration of its length-tension curve (Starling's Law). Because the subsequent straightening of the eye produces a movement of the new insertions of the rectus muscles either anteriorly or posteriorly in the orbit, the actual amount of tightening or shortening of the muscle is not equal to the amount of recession or resection. How much this phenomenon alters the true amount of tightening or shortening of a muscle has important implications in the determination of safe amounts of surgery, which may differ if one is operating on the fixing or non-fixing eye. In addition, the size of the globe should have an important role in determining the response per millimeter of surgery.