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L. F. Dell'Osso, Z. I. Wang, J. B. Jacobs; Idiosyncratic Gaze-Angle Variation of Infantile Nystagmus Syndrome Waveform Amplitude Guided by Alexander's Law Embodied in a Behavioral Model Ocular Motor System Model. Invest. Ophthalmol. Vis. Sci. 2007;48(13):876.
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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 the variation of IN amplitude with gaze angle.
In a previous study, gaze-angle effects in Fusion Maldevelopment Nystagmus Syndrome (i.e., foveating and defoveating fast-phase alternation) waveforms were simulated, guided by Alexander’s law input. Alexander’s law describes the increase in the amplitude of nystagmus as the eye is moved in the direction of the fast phase. In the current study, fixation data from INS subjects at various gaze angles were examined and used as templates for the simulations. All simulations were performed in the MATLAB Simulink environment. The original OMS model is available online at http://www.omlab.org.
The Alexander’s law functional block in the internal monitor of the OMS model is based on a tonic imbalance signal and efference copy of eye position signal. In INS, the "null" position and sharpness could be approximated by the two Alexander’s law relationships (one for each direction), with their intersection indicating the "null" position and the slopes of the curves controlling the broadness of the "null." At various gaze angles, these Alexander’s law relationships influenced the slow-phase amplitude of IN waveforms differently, thus mimicking the same gaze-angle effects as we observed in INS patients.
The behavioral output of the OMS model demonstrated the effectiveness of using Alexander’s law input to simulate the variation of IN waveforms across the whole visual domain. This improvement in the OMS model adds another step in the implementation of a complete and idiosyncratic OMS model that can simulate normal as well as pathological (i.e., INS) behaviors.
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