title: Mirror-image optic nerve dysplasia with associated anisometropia in identical twins.
abstract: BACKGROUND
  Monozygotic (MZ) or "identical" twins arise from a single fertilized egg, which divides into two embryos at an early stage of development. As a result, MZ twins have identical genomes and are always of the same sex.
  
  
  METHODS
  A case of optic nerve hypoplasia and anisometropia, in association with mirror-image presentation in a set of 12-year-old identical twins, is reported. The monozygotic twinning event responsible for identical twins--as well as the rare phenomenon of mirror imaging--is described.
  
  
  RESULTS
  The combined occurrence of anisometropia and optic nerve hypoplasia in mirror-image presentation in a set of monozygotic twins provides a unique opportunity to study the genetic versus environmental influences on the development of optic nerve hypoplasia.
  
  
  CONCLUSIONS
  Although the cause of optic nerve hypoplasia remains unclear, its associated mirror-image presentation in this case suggests a possible genetic predisposition.
authors.affiliation: State University of New York, State College of Optometry, New York 10010, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Cidis
authors.forename: J H
authors.initials: JH
authors.lastname: Warshowsky
authors.forename: S G
authors.initials: SG
authors.lastname: Goldrich
authors.forename: C C
authors.initials: CC
authors.lastname: Meltzer
mesh_terms: D015858:Anisometropia / Q000175:diagnosis / Q000235:genetics*; D002648:Child; D004200:Diseases in Twins; D005074:Evoked Potentials, Visual; D005260:Female; D006801:Humans; D009900:Optic Nerve / Q000002:abnormalities* / Q000473:pathology; D009901:Optic Nerve Diseases / Q000175:diagnosis / Q000235:genetics*; D014430:Twins, Monozygotic; D014792:Visual Acuity; D014796:Visual Perception