ABSTRACT
Eleven pairs of monozygotic twins with strabismus were retrospectively selected to investigate binocular function. All pairs underwent fully ophthalmologic assessments. Six of 11 pairs were concordant and sensory tests revealed the same responses. The remaining five pairs were discordant. One pairs of them had the combination of intermittent exotropia and orthophoria. Four pairs of them had the combination of various esotropia and orthophoria. All of members without manifest esodeviation had a suppression scotoma in one eye and none of them had fine stereopsis of 60 sec of arc or better. Although all members with esotropia underwent successful interventions to be aligned orthophoric or esophoric, they showed subnormal binocularity suggesting monofixation syndrome. It is considered that primary monofixation syndrome is a congenital and genetic basis for various esotropia and may be consecutive to be manifestly deviated with acquired multi-factors.
