Unilateral aplasia of a lateral rectus muscle

Abstract

The congenital absence of an extraocular muscle is rare. The case of an unilateral lateral rectus muscle and a review of the literature are presented. A healthy 7-year old boy with inconspicuous family history was seen in our clinic. The boy had been noted to have a right esotropia from infancy. Clinical orthoptical examinations and magnetic resonance imaging (MRI) were performed. The esotropia was corrected by transposition of the superior and inferior rectus muscle. With correction of the myopic astigmatism the visual acuity of either eye was 0.8. The right eye could not abduct to pass the midline, the left eye passed the midline by 35 degrees. From the primary position the right eye was able to elevate by 20 degrees and the left eye to elevate 15 degrees. The alternate prism and cover test showed in either eye fixation an esotropia of 24 degrees without significant change in elevation or depression. Besides, there was a hypertropia (+VD) of 14 degrees which increased to 21 degrees in left gaze and decreased to 0 degree in right gaze. Indirect ophthalmoscopy showed a bilateral excyclo position of approximately 5-10 degrees. Retraction of either eye was not seen in any gaze direction. The axial length of the right/left eye was 25.2 mm/24.6 mm. Aplasia of the right lateral rectus muscle and hypoplasia of the left lateral rectus muscle could be demonstrated by magnetic resonance imaging. Intraoperatively the right lateral rectus muscle was absent. The vertical eye muscle inserted regularly. Hummelsheim's procedure was performed. Eight months postoperatively, the boy was orthotropic in primary position. The inferior oblique overaction was still present together with a "V" pattern of 8 degrees. The Bagolini test was positive. The congenital absence of one or more extraocular muscles is a rare condition, which has to be considered as a differential diagnosis to neurogenic nerve palsy.