A case of aplasia of inferior rectus muscle

Purpose : To report a case of aplasia of inferior rectus muscle detected at an advanced age. Case : A 73-year-old female had superior displacement of her right eye since birth that exacerbated recently. Findings : Her corrected visual acuity was 0.1 right and 0.8 left. The right eye was displaced superior-temporally at the primary position. Ocular motility was restricted in 5 directions except superiorly, presented with exacerbation of superior displacement of her right eye. Magnetic resonance imaging (MRI) showed absence of inferior rectus muscle in the right eye, atrophy of superior rectus and levator muscle, and constriction in the posterior portion of medical rectus muscle. There was no polymorphism of ARIX and PHOX2B genes. Transposition of horizontal muscles in the right eye resulted in alignment in the primary position and improved right visual acuity to 0.7. Reported Cases : There are 16 cases of aplasia of inferior rectus muscle reported in Japan. The series comprised 4 males, 8 females, and unknown in 4 cases. Associated lesion included microcornea, nanophthalmos, displaced pupil, and choroidal coloboma. Conclusion : Aplasia of inferior rectus muscle is a possibility when limitation in downward gaze is present. Forced duction test and MRI are useful adjunct diagnostic modalities.