VEP asymmetry with ophthalmological and MRI findings in two achiasmatic children |
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Authors: | Jelka Brecelj Branka Stirn-Kranjc Nuška Pečarič-Meglič Miha Škrbec |
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Institution: | (1) Unit for Visual Electrophysiology, Eye Clinic, University Medical Centre, 1525 Ljubljana, Slovenia;(2) Clinical Institute for Radiology, University Medical Centre, Ljubljana, Slovenia |
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Abstract: | Achiasmia is a rarely diagnosed visual pathway maldevelopment where all or the majority of nasal retinal fibres fail to decussate
at the optic chiasm. It has been identified by neuroimaging and also by visual evoked potential (VEP) asymmetry. VEP asymmetry
has not been defined consistently in previous studies. The aim was to study VEP asymmetry to flash stimulation in two children
with maldevelopment of the optic chiasm in comparison to control children. Both children had congenital nystagmus, optic nerve
hypoplasia with a bilateral small double ring, bitemporal visual field defect and normal colour vision. In child 1 visual
acuity in both eyes was 0.1, in child 2 it was 0.2. MRI showed reduced chiasmal size in child 1, while in child 2 it was combined
with other midline abnormalities. VEP to monocular flash stimulation showed in both children distinctive occipital distribution,
which was not observed in control children. The N2 wave was distributed asymmetrically over the ipsilateral hemisphere to
the stimulated eye, while the P2 wave was distributed over both hemispheres. The P2 wave was however better defined over the
ipsilateral hemisphere. Flash VEP occipital distribution remained similar in child 1, who was followed from 10 months to 9 years.
These cases of achiasmia demonstrate a distinctive VEP asymmetry in the distribution of the flash VEP N2 wave, as well as
the expected structural defect determined by neuroimaging. |
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Keywords: | Achiasmia Bitemporal visual field defect Nystagmus Optic nerve hypoplasia Optic chiasm Septo-optic dysplasia Visual evoked potentials |
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