Visual-evoked potential evidence of chiasmal hypoplasia

Purpose: To show that chiasmal hypoplasia or aplasia need not be an isolate d developmental anomaly and to examine the spectrum of associated clinical findings to explore the possibility that these patients may represent a phe notypic manifestation of a developmental gene anomaly. Design: An observational case series, Participants: Five infants, between several weeks and 7 months of age, in w hom the electrophysiologic characteristic of chiasmal hypoplasia had been n oted were included, Methods: Flash electroretinography and flash and pattern visual-evoked pote ntials (VEPs) were elicited from all patients. Clinical ophthalmologic exam inations, including funduscopy, were performed, and all patients had magnet ic resonance imaging (MRI) brain scans. Main Outcome Measures: 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 occ ipital distribution, which is consistent with a paucity of fibers crossing at the chiasm, The MRI findings supported this electrophysiologic observati on, illustrating degrees of chiasmal hypoplasia and variable coincidence of other midline abnormalities of the brain. Optic disc appearances varied fr om normal to hypoplastic and colobomatous, Conclusions: The ophthalmologic and MRI findings of five patients who showe d a crossed asymmetry in monocular flash VEPs are consistent with a paucity of axons crossing at the chiasm, The similarities between achiasmia in hum ans and mice due to a Pax2 gene anomaly are discussed.