Case report: Unilateral optic nerve aplasia and developmental hemi-chiasmal dysplasia with VEP misrouting
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CLINICAL CASE REPORT
Case report: Unilateral optic nerve aplasia and developmental hemi-chiasmal dysplasia with VEP misrouting Sian E. Handley . Oliver R. Marmoy Dorothy A. Thompson
. Sri K. Gore
. Kshitij Mankad
.
Received: 7 April 2020 / Accepted: 7 August 2020 Ó The Author(s) 2020
Abstract Purpose To describe the trans-occipital asymmetries of pattern and flash visual evoked potentials (VEPs), in an infant with MRI findings of unilateral optic nerve aplasia and hemi-chiasm dysplasia. Methods A child with suspected left cystic microphthalmia, left microcornea, left unilateral optic nerve aplasia, and hemi-chiasm underwent a multi-channel VEP assessment with pattern reversal, pattern onset, and flash stimulation at the age of 16 weeks. Results There was no VEP evidence of any postretinal visual pathway activation from left eye with optic nerve aplasia. The VEP trans-occipital distribution from the functional right eye was skewed markedly across the midline, in keeping with significant misrouting of optic nerve fibres at the chiasm. This was supported by the anatomical trajectory of the optic chiasm and tracts seen on MRI. S. E. Handley O. R. Marmoy S. K. Gore K. Mankad D. A. Thompson Clinical and Academic Department of Ophthalmology, Great Ormond Street Hospital for Children, Great Ormond Street, London WC1N 3JH, UK S. E. Handley (&) K. Mankad D. A. Thompson UCL Great Ormond Street Institute of Child Health, University College London, 30 Guildford Street, London WC1N 1EH, UK e-mail: [email protected] O. R. Marmoy Manchester Metropolitan University, Manchester, UK
Conclusion This infant has chiasmal misrouting in association with unilateral optic nerve aplasia and unilateral microphthalmos. Chiasmal misrouting has not been found in patients with microphthalmos or anophthalmos, but has been reported after early eye loss in animal models. Our findings contribute to our understanding of the discrepancy between the visual pathway physiology of human unilateral microphthalmia and animal models. Keywords Chiasm Hemi-chiasm Misrouting Optic nerve aplasia Visual evoked potential
Introduction In humans, fully functional binocular vision relies upon the correct formation of the optic chiasm. At the chiasm, a designated proportion of retinal ganglion cell axons from the nasal retina of each eye must project across the midline to innervate the contralateral hemisphere, representing the bi-temporal field. The remaining proportion of fibres from the temporal retina of each eye project to the ipsilateral hemisphere and represent the bi-nasal fields. The correct development of these crossing and non-crossing chiasmal pathways relies upon the temporo-spatial and dosagedependent interaction of many guidance cues [1, 2]. The two major conditions associated with a
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disproportion of fibres at the chiasm are chiasmal aplasia or hypoplasia (non-decussating retinal fugal fibre syndrome) [3] in which there is absent or markedly reduced
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