一卵性双生児の斜視の表現型

Phenotype of strabismus in a pair of monozygotic twins

要約　背景：多胎児での斜視には遺伝の関与があり，表現型が鏡像を呈することがある。目的：斜視の表現型が鏡像を呈した一卵性双生児の報告。症例：31歳の一卵性双生児の姉妹を検索した。両名とも飲酒時に上下複視があり，第二子（妹）は傾眠時と疲労時に上下または水平方向の複視を自覚している。所見：姉妹ともに矯正視力は1.2または1.5で，姉には－2Dと－1.25D，妹には－2Dと－3Dの近視がある。姉は左眼が固視眼，妹は右眼が固視眼である。平常時には姉は外斜位，妹は間欠性外斜視である。飲酒時には両名とも内斜視になり，非固視眼が上転し，立体視が不良になった。結論：一卵性双生児である成人姉妹に斜視または斜位があり，その表現型が鏡像を呈した。

Abstract.　Background：Hereditary factors may be involved in strabismus in multiple births. Phenotype in these cases may present mirror image. Purpose：To report a pair of monozygotic twins who manifested mirror image of strabismus. Cases：This study was made on a pair of female monozygotic twins. Both had vertical diplopia when inebriated. The second-born sister noticed vertical or horizontal diplopia during fatigue or sleepiness. Findings：Both had corrected visual acuity of 1.2 or 1.5 in either eye. The first-born had myopia of －2 and －1.25 diopters and was fixating with the left eye. The second-born had myopia of －2 and －3 diopters and was fixating with the right eye. When free of alcoholic influence,the first-born had exophoria and the second-born had intermittent exotropia. After intake of alcohol,both manifested esotropia with sursumduction of nonfixating eye and with poor stereopsis. Conclusion：This pair of monozygotic twins had tropia or phobia and manifested mirror image as phenotype.