How Do Recessions and Resections of Extraocular Muscles Work?

Abstract

almology R ecessions and resections of extraocular mu classically thought to alter eye alignment b ing the force that the muscles can genera cording to Starling’s law, shortening a muscle, with a recession, decreases both the elastic and tractile force in the muscle; stretching a muscle, with a resection, increases the elastic and co forces. Although this classic concept has been accepted for many years, it is inconsistent with alities regarding extraocular muscle surgery. For most surgical formulas for extraocular muscle r are not linear. As the amount of recession ap some “maximum amount” (possibly by placing th near the equator) there is an almost “knife-edge” effect of the surgery. This observation is not c with the known length–tension curve for extraocu cles nor can it be explained solely by a reduction of contact. More importantly, this classic teach not take into account the induced effects that und occur with eye muscle surgery. For example, if th rectus muscle is recessed in an esotropic eye, th will initially be shortened. However, if the straightens as a result of the surgery, the new inse of the recessed muscle will rotate forward in the result of the eye straightening. This will stretch o of the shortening that had initially occurred. At time, the insertion of the unoperated antagoni rectus muscle will rotate posteriorly in the or shortening that unoperated muscle. Dependin size of the globe, the amount of recession, and th of straightening that occurs, the actual shorten occurs in the unoperated lateral rectus muscle greater than the amount that actually occurs in cessed medical rectus muscle in the aforemention ple. Clearly the classic understanding of how ex muscle surgery works is erroneous or incomplet The torque vector theory set forth by Miller a in this issue of JAAPOS may represent a major ward in reconciling some of these inconsistenci