Abstract
We expanded the original behavioral Ocular Motor System (OMS) model for Infantile Nystagmus Syndrome (INS) by incorporating common types of jerk waveforms within a unifying mechanism. Alexander’s law relationships were used to produce desired INS null positions and sharpness. At various gaze angles, these relationships influenced the IN slow-phase amplitudes differently, thereby mimicking the gaze-angle effects of INS patients. Transitions from pseudopendular with foveating saccades to jerk waveforms required replacing braking saccades with foveating fast phases and adding a resettable neural integrator in the pursuit pre-motor circuitry. The robust simulations of accurate OMS behavior in the presence of diverse INS waveforms demonstrate that they can all be generated by a loss of pursuit-system damping, supporting this hypothetical origin.
Highlights
Emphasis is put less on where each functional block is located and more on and how they work together under organizing principles resulting in known ocular motor system behaviors. (These publications contain block diagrams of prior versions that may be compared with Figures 1 and 9)
Varying the Alexander’s Law slope produces differing amounts of Alexander’s Law effect. This effect leads to slowphase velocity increases as gaze is directed in the abducting direction of the fixating eye, and that would cause the transition from foveating to defoveating fast phases in Fusion Maldevelopment Nystagmus Syndrome (FMNS) (Dell'Osso & Jacobs, 2001)
This study and resulting model strongly support the hypothesis that both pendular and jerk waveforms can be generated by the same pursuit-system instability and that most Infantile Nystagmus Syndrome (INS) waveforms are due to a loss of pursuit-system damping
Summary
The original ocular motor system (OMS) model (and the subsequent versions published in our studies) is a top-down, control systems model reproducing the ocular motor responses of normal individuals as well as those with several INS waveforms (Jacobs & Dell'Osso, 2004). This behavioral OMS model evolved from earlier models that were based on years of observation and analysis of normal and abnormal eyemovement data (Dell'Osso, 2002b); wherever applicable, adherence to known anatomical structure was maintained.
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