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Updated: Dec 14, 2025
Stimulus-specific Cortical Visual Evoked Potential Morphological Patterns
Published on: May 12, 2019
Pattern-onset and OFFset visual evoked potentials in the diagnosis of hemianopic field defects
Oliver R Marmoy1,2, Sian E Handley3,4, Dorothy A Thompson3,4
1Tony Kriss Visual Electrophysiology Unit, Clinical and Academic, Department of Ophthalmology, Great Ormond Street Hospital for Children, London, WC1N 3JH, UK. O.Marmoy@nhs.net.
Background:
Visual evoked potentials (VEPs) assess the function of the visual pathway from the retina to the primary visual cortex. There is much evidence that monocular pattern-reversal and flash VEPs can distinguish dysfunction due to chiasmal and post-chiasmal afferent pathway lesions. There is less evidence about the use of pattern-onset/OFFset VEPs to identify post-chiasmic dysfunction.
Methods:
We present nine patients with a range of visual pathway defects that caused dense hemianopic field defects. These patients had pattern onset-OFFset VEPs recorded from an array of occipital electrodes referred to a mid-frontal electrode to checks that appeared for 230 ms and disappeared for 300 ms into a background of mean luminance, in a stimulus field of 30°.
Results:
We found pattern-onset VEP components lateralise to occipital electrodes overlaying the functional hemisphere, whereas pattern-OFFset VEP components demonstrate the paradoxical lateralisation phenomenon, described in reversal VEPs, and are maximal over the contralateral occiput.
Conclusion:
Our findings show how extending the recording time window to include an OFFset VEP facilitates identification of hemianopic visual field defects. We advocate the pattern-onset/OFFset VEP in the assessment of patients with hemianopia, having particular value for patients who are otherwise unable to perform more demanding half-field electrophysiology, imaging or psychophysical testing.
