Mirror Image Chorioretinal Colobomas in Identical Twins

Abstract

78 n monozygotic twins, the splitting of the zygote occurs between the 8 and 16-cell stages of embryonic development. The mirror-image phenomenon (i.e. expression of features or anomalies on opposite sides) may occur in case of a possible delay in this process.1 This phenomenon may result from genetic or environmental factors that occur before the split into two monozygotic embryos.2 The mirror-image phenomenon is observed only in identical twins, and in approximately 25% of monozygotic twins.3 The mirror-image phenomenon rarely affects ophthalmic features.1 To the best of our knowledge, there have been no reported cases of chorioretinal coloboma in monozygotic twins.