Compartmentalization of Superior Oblique (SO) Muscle Function Has Implications for Superior Oblique Palsy

Introduction: Intramuscular innervation of horizontal rectus extraocular muscles is divided into inferior and superior divisions innervating non-overlapping compartments of parallel-oriented muscle and tendon fibers. Functional magnetic resonance imaging (MRI) has demonstrated differential contractile function of horizontal rectus compartments during vertical duction, convergence, and ocular counter-rolling, as well as selective neurogenic atrophy in superior compartment lateral rectus palsy. We sought evidence of compartmental specialization in the SO, suspecting that selective damage to one or the other compartment might underlie some of the variation in clinical presentations of SO palsy.