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L.F. Dell'Osso, Z. Wang, J.B. Jacobs; A Unifying Hypothesis for Infantile Nystagmus Syndrome Embodied in a Behavioral Model: Pendular and Jerk Waveforms From the Same Pursuit–System Deficit . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2657.
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© ARVO (1962-2015); The Authors (2016-present)
To expand the behavioral Ocular Motor System (OMS) model for Infantile Nystagmus Syndrome (INS) by incorporating J (Jerk) and Jef (Jerk with extended foveation) waveforms, demonstrating the common smooth–pursuit origin of both pendular and jerk waveforms. The original OMS–model of INS simulated the responses of individuals with several pendular waveforms based on an hypothesized exacerbation of the normal pursuit–subsystem instability and its interaction with other OMS components.
Fixation data from INS subjects were used as templates for the simulations that were performed in the MATLAB Simulink environment.
The use of a resettable neural integrator in the pre–motor pursuit circuitry enabled the resetting of the underlying pendular oscillation after each foveating saccade, which gave rise to J waveforms. The fixation subsystem remained responsible for prolonging the low–velocity intervals of foveation in J and Jef waveforms. The conception of a resettable neural integrator is in accordance with the following observations: 1) INS subjects with J or Jef waveforms switch to pendular waveforms when inattention occurs; and 2) with verbal prompting, the ability to generate foveating saccades is regained and the waveforms instantly revert back to J or Jef. The model’s responses to target steps, pulse–steps, ramps, and step–ramps were comparable to human eye–movement data.
The OMS model’s robustness demonstrates that both pendular and jerk waveforms could be generated by the same pursuit–system instability, which supports the hypothesis that many pendular and jerk INS waveforms are due to a loss of pursuit–system damping. The inclusion of a resettable neural integrator allows the OMS model to simulate idiosyncratic and psychological factors. Modelling OMS dysfunction, e.g. INS, has provided valuable insight into the functional structure of the OMS under both normal and pathological conditions.
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