下直筋欠損の1例

A case of aplasia of inferior rectus muscle

要約　目的：下直筋欠損が高齢になって発見された症例の報告。症例：73歳女性が幼時からあった右眼の上転が顕著化したため受診した。所見：矯正視力は右0.1，左0.8であり，第1眼位で右眼が上外側に偏位し，上方以外の5方向に眼球運動制限があり，潜伏眼振があった。磁気共鳴画像検査（MRI）で右眼の下眼筋が欠損し，上直筋と眼瞼挙筋に萎縮があり，内直筋の後部にくびれがあった。ARIXとPHOX2B遺伝子エクソンの塩基変化はなかった。右眼に水平筋移動術を行い，眼位が正常化し，右眼視力が0.7pに上昇した。過去の報告例：日本では下直筋欠損につき16例の報告がある。男性4例，女性8例，不明4例で，小角膜，小眼球，瞳孔偏位，脈絡膜欠損などが併発している。結論：下転障害の症例では，MRIや牽引試験を行い，下直筋欠損と鑑別する必要がある。

Abstract.　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.