title: The achiasmia spectrum: congenitally reduced chiasmal decussation.
abstract: OBJECTIVE
  To describe the clinical spectrum of achiasmia, a congenital disorder of reduced relative decussation at the optic chiasm.
  
  
  METHODS
  A retrospective case note and patient review of nine children (four boys). Achiasmia was defined by the combination of a characteristic asymmetry of the monocular visual evoked potential (VEP) response to flash and neuroimaging showing reduced chiasmal size.
  
  
  RESULTS
  Three of the children had an associated skull base encephalocele with agenesis of the corpus callosum. In two patients achiasmia was associated with septo-optic dysplasia. Three patients had no neuroimaging abnormalities other than reduced chiasmal size and have no known pituitary dysfunction. One child had multiple physical deformities but the only brain imaging abnormality was reduced chiasmal size.
  
  
  CONCLUSIONS
  Some children with disorders of midline central nervous system development, including septo-optic dysplasia and skull base encephaloceles, have congenitally reduced chiasmal decussation. Reduced relative decussation may co-exist with overall chiasmal hypoplasia. Children with an apparently isolated chiasmal decussation deficit may have other subtle neurological findings, but our clinical impression is that most of these children function well.
authors.affiliation: Visual Sciences Unit, Institute of Child Health University College, London WC1N 1EH, UK.
authors.forename: D A
authors.initials: DA
authors.lastname: Sami
authors.forename: D
authors.initials: D
authors.lastname: Saunders
authors.forename: D A
authors.initials: DA
authors.lastname: Thompson
authors.forename: I M
authors.initials: IM
authors.lastname: Russell-Eggitt
authors.forename: K K
authors.initials: KK
authors.lastname: Nischal
authors.forename: G
authors.initials: G
authors.lastname: Jeffrey
authors.forename: G
authors.initials: G
authors.lastname: Jeffery
authors.forename: M
authors.initials: M
authors.lastname: Dattani
authors.forename: R A
authors.initials: RA
authors.lastname: Clement
authors.forename: A
authors.initials: A
authors.lastname: Liasis
authors.forename: A
authors.initials: A
authors.lastname: Liassis
authors.forename: D S
authors.initials: DS
authors.lastname: Taylor
mesh_terms: D000015:Abnormalities, Multiple; D000293:Adolescent; D061085:Agenesis of Corpus Callosum; D002648:Child; D002675:Child, Preschool; D004677:Encephalocele / Q000503:physiopathology; D005074:Evoked Potentials, Visual; D005133:Eye Movements; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009897:Optic Chiasm / Q000002:abnormalities* / Q000473:pathology; D012189:Retrospective Studies; D019291:Skull Base / Q000002:abnormalities; D014792:Visual Acuity; D014794:Visual Fields