Bifid Medial Rectus Muscle Insertion Associated With Intermittent Distance Exotropia

Abstract

6-YEAR-OLD GIRL with an intermittentdistanceexotropia measuring 40 prism diopters with no associated systemic abnormalities underwent corrective squint surgery. Peroperatively, she was found to have an anomalous bifid left medial rectus muscle insertion composed of 2 distinct parallel muscular heads and insertions originating from 1 common origin (Figure). Thenarrowersuperiorlimbofthe bifid muscle measured 3-mm wide andwasinserted5mmfromthelimbus,whilethewiderinferiorlimbof the bifid muscle measured 5-mm wide and was inserted 5.5 mm from the limbus. This finding required a modification of the planned surgical procedure. Both limbs of the anomalous medial rectus were resected by 4 mm and sutured together to reformasinglecontinuousmuscleinsertion. The lateral rectus was recessed 6 mm from its insertion. Fourteen months’ postoperatively, her ocular alignment was improved and stable, with a distance exodeviation of 16 prism diopters. COMMENT Oblique and vertical rectus muscle anomalies have commonly been reported in patients with craniofacial syndromes, 1,2 while horizontal rectus muscle anomalies have uncommonly been associated with such syndromes. 3 A bifid left medial rectus muscle insertion found at the time of surgeryhaspreviouslybeenreportedin a child with Crouzon syndrome (characterizedbythetriadofcraniosynostosis,midfacialhypoplasia,and exophthalmos). 4 Our case demonstrates that anomalies of extraocular muscles may also rarely be present in patients without craniofacial syndromes, and strabismus surgeons should be prepared to modify their surgical plan when anomalous extraocular muscles are found.