Magnetic Resonance Imaging in Strabismus

Abstract

Diagnostic imaging of the orbit, extraocular muscles (EOM) and ocular adnexa in complex strabismus often provides insight into its etiology. High resolution dynamic MRI has demonstrated that the direction of action of each rectus EOM is directed towards an anteriorly located connective tissue sleeve containing elastin, collagen and richly innervated smooth muscle tissue called a pulley. Anatomically, global layer of rectus EOM passes through the pulley and the orbital layer inserts on the pulley and not on the globe. Pulley heterotopy thus is an important parameter in the genesis of different forms of complex strabismus previously classified as being idiopathic. Evaluation of these changes in vivo with dynamic high resolution MRI aids planning of appropriate corrective measures, focused on amelioration of the primary anomaly, which can often not be clinically assessed. Target fixation while performing MRI in different gazes with the orbital surface coil aids evaluation of the dynamic contractility of the EOMs, thus demonstrating objective parameters of EOM function. The detailed anatomical and functional parameters thus determined by this non-invasive modality not only provides unique insights into the etiopathogenesis of the strabismus, especially complex strabismus but also provides objective evidence based guidelines for their management. This review elaborates on the concept of pulleys and the diagnostic importance of dynamic high resolution surface coil MRI in the diagnosis and management of complex strabismus with specific emphasis on disorders of pulley heterotopy, cranial nerve palsy, extraocular muscle trauma and the genesis and management of the sagging eye syndrome.