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MV Joosse, S Verspeek, RJ Schimshiemer, M Vermeulen, HM van Minderhout; Visual Event-related Potentials in Strabismic Suppression . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2942.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Suppression is the powerful defence mechanism against the unpleasant sensation of diplopia in cross eyedness. It can only be measured under binocular viewing conditions. In this study we objectify strabismic suppression by means of electrophysiological analysis. Through this experiment we also try to gain more insight into which cortical areas are involved in the process of suppression. Methods: Measurements were performed in 10 persons with either convergent or divergent strabismus and in 4 normal control persons. Under binocular viewing conditions, the subjects had a haploscopic view of 2 fusable identical contrastful images, through which 4 lights could be presented. Under monocular viewing conditions one eye was occluded and the lights were presented to the other eye. The stimulus lights had a sinusoidal luminance profile with a duration of 500 msec. With 8 surface electrodes on the posterior third of the skull (3 occipital, 3 parietal and 2 temporal) potentials were recorded upon light stimulation of each eye under monocular as well as under binocular viewing conditions. Results: We found a characteristic triphasic complex of approximately 200msec, that occurred 80 msec after the onset of the triggering light pulse in all subjects under all 4 conditions, except for stimulation of the non-fixating eye under binocular viewing conditions. In 6 of the 10 subjects no response complex could be detected under these conditions. In these subjects there was absence of the response across all 8 leads. In the 4 other test subjects no significant difference in response between monocular and binocular viewing could be found. Conclusion: Suppression involves some sort of neuronal switch, that turns off the activity of a rather large part of the cortex under binocular viewing conditions. Futher research is needed to elicit the exact location of this switch.
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