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Muriel Dysli, Mathias Abegg, Department of Ophthalmology; Plasticity of the Vergence Response. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2581.
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© ARVO (1962-2015); The Authors (2016-present)
Vergence movements are slow disconjugate eye movements which may be triggered by image disparity or accommodation. There exist numerous clinical contexts where image disparity may vary with the direction of gaze. A common example is a sixth cranial nerve palsy with increasing image disparity in gaze toward the affected muscle. Adaptive changes to such incomitant image disparity have been poorly investigated and are the scope of this study.
Vergence stimuli of gaze dependent magnitude were used to mimic the image disparity of an incomitant strabismus. In a first experiment prisms were placed such that stimuli were viewed through the prisms in one gaze direction but not in the other gaze directions. In a second experiment we used a haploscope to modify image disparity according to gaze. We measured vergence responses that were made after a saccade shifting gaze from left to right, with increased image disparity in right gaze. We analysed changes of rise time or slope, latency, and amplitude over time.
Increased image disparity in right gaze led to a decrease of vergence rise time (p=0.055) and latency (p=0.048) within minutes. Using the haploscope to deliver vergence stimuli, we again found a significant increase in slope (p<0.001), but not in latency (p=0.336).
In this study we show that repetitive increase of the vergence demand leads to rapid improvement of the vergence response kinetics with a moderate effect on the latency. This novel type of vergence plasticity helps to rapidly restore stereovision after a saccade is made into a field of gaze with increased image disparity.
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