title: Visual-evoked potential evidence of chiasmal hypoplasia.
abstract: OBJECTIVE
  To show that chiasmal hypoplasia or aplasia need not be an isolated developmental anomaly and to examine the spectrum of associated clinical findings to explore the possibility that these patients may represent a phenotypic manifestation of a developmental gene anomaly.
  
  
  METHODS
  An observational case series.
  
  
  METHODS
  Five infants, between several weeks and 7 months of age, in whom the electrophysiologic characteristic of chiasmal hypoplasia had been noted were included.
  
  
  METHODS
  Flash electroretinography and flash and pattern visual-evoked potentials (VEPs) were elicited from all patients. Clinical ophthalmologic examinations, including funduscopy, were performed, and all patients had magnetic resonance imaging (MRI) brain scans.
  
  
  METHODS
  The occipital distribution of monocular VEP response peaks was studied. The symmetry of lateral channel responses was compared for monocular stimulation.
  
  
  RESULTS
  All five patients had a crossed asymmetry in the monocular VEP occipital distribution, which is consistent with a paucity of fibers crossing at the chiasm. The MRI findings supported this electrophysiologic observation, illustrating degrees of chiasmal hypoplasia and variable coincidence of other midline abnormalities of the brain. Optic disc appearances varied from normal to hypoplastic and colobomatous.
  
  
  CONCLUSIONS
  The ophthalmologic and MRI findings of five patients who showed a crossed asymmetry in monocular flash VEPs are consistent with a paucity of axons crossing at the chiasm. The similarities between achiasmia in humans and mice due to a Pax2 gene anomaly are discussed.
authors.affiliation: Ophthalmology Department, Great Ormond Street Hospital NHS Trust, London, England. d.thompson@vissci.ion.ucl.ac.uk
authors.forename: D A
authors.initials: DA
authors.lastname: Thompson
authors.forename: A
authors.initials: A
authors.lastname: Kriss
authors.forename: K
authors.initials: K
authors.lastname: Chong
authors.forename: C
authors.initials: C
authors.lastname: Harris
authors.forename: I
authors.initials: I
authors.lastname: Russell-Eggitt
authors.forename: F
authors.initials: F
authors.lastname: Shawkat
authors.forename: B G
authors.initials: BG
authors.lastname: Neville
authors.forename: W
authors.initials: W
authors.lastname: Aclimandos
authors.forename: D S
authors.initials: DS
authors.lastname: Taylor
mesh_terms: D003103:Coloboma / Q000175:diagnosis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D004596:Electroretinography; D005074:Evoked Potentials, Visual; D005124:Eye Abnormalities / Q000175:diagnosis* / Q000235:genetics; D005260:Female; D006801:Humans; D007223:Infant; D008279:Magnetic Resonance Imaging; D008297:Male; D009897:Optic Chiasm / Q000002:abnormalities* / Q000473:pathology; D009898:Optic Disk / Q000002:abnormalities*; D009901:Optic Nerve Diseases / Q000175:diagnosis* / Q000235:genetics; D051762:PAX2 Transcription Factor; D010775:Photic Stimulation; D014157:Transcription Factors / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D051762:PAX2 Transcription Factor; C497318:PAX2 protein, human; D014157:Transcription Factors