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Christopher W. Tyler, Anas Elsaid, Lora Likova, Spero Nicholas; Analysis of Human Vergence Dynamics. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4869.
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© ARVO (1962-2015); The Authors (2016-present)
Binocular vergence is controlled by a mix of disparity, accommodative and proximal vergence cues. Peak vergence velocities are an order of magnitude slower than conjugate saccades, with similar onset latencies, and frequent saccadic intrusions particularly for asymmetrical vergence movements. Here we estimate the distribution of symmetrical vergence dynamics parameters in a large population of fifty normal volunteers.
The symmetrical disparity vergence stimulus consisted disparity jumps of ± 2° of a combined central fixation target and surrounding random-dot field at unpredictable intervals varying from 2-3 s. The study also included 0.25 Hz sinusoidal vergence and versional tracking tasks for the same stimuli. Binocular eye movements were recorded with a dual infrared limbal eye tracker. The subjects were assessed for stereopsis, strabismus and a past history of traumatic brain injury (TBI).
Most subjects were able to perform the disparity jump and sinusoidal tracking tasks with approximately symmetrical vergence movements, with relatively few saccadic intrusions. For the disparity jumps, the peak vergence velocities averaged about 8 deg/s for convergence (and marginally slower for divergence), being thus a factor of ~5 slower than saccades for this amplitude (1° in each eye), having durations of about 400 ms. A substantial subpopulation (with no strabismus or TBI) showed an inability to make prompt divergence movements in one eye, using an anomalous ‘inverse priming’ strategy for divergence, involving an interplay of convergence and glissade movements followed by larger uniocular divergence to achieve the required divergence angle. Mostly, the time courses of these anomalous movements were non-saccadic with typical vergence dynamics, despite being predominantly uniocular. A different subgroup with a history of TBI had either convergence or divergence movements (or both) of much reduced velocity and increased duration (500-2000 ms).
There was a wide variety of ‘normal’ vergence dynamics, from matching convergence/divergence dynamics to anomalous inverse priming strategies to overcome uniocular vergence deficits. Subject with a history of recent TBI dramatic slowing of the vergence dynamics. The results are important for understanding the range of binocular coordination dynamics that should be expected in the normal population and the analysis of oculomotor control deficits in the TBI population.
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