A unifying hypothesis for the multiple waveforms of infantile nystagmus and their idiosyncratic variation with gaze angle and therapy

Infantile Nystagmus Syndrome (INS) is an ocular motor instability characterized by involuntary oscillations of the eyes. The purpose of this thesis is to better understand the underlying mechanisms of INS in terms of static characteristics, dynamic properties, and changes after extraocular muscle (EOM) surgeries, and to incorporate these findings into a behavioral Ocular Motor System (OMS) model. Accurate recordings of eye-movement responses to visual stimuli under certain experimental paradigms were analyzed and used as templates for model simulations. The effectiveness of the four-muscle tenotomy surgical procedure was evaluated and the post-surgical effects were categorized in order to set up the clinical criteria governing the use of this procedure. Also, combination of tenotomy with other commonly practiced strabismus/nystagmus surgeries was explored. The eXpanded Nystagmus Acuity Function (NAFX), which is a mathematical function that linearly relates foveation quality of nystagmus waveforms to the maximum possible visual acuity, was used as the direct measurement of post-surgical waveform changes. The differential effect of tenotomy on the fast and slow eye movements of INS was carefully examined to elucidate a working mechanism for tenotomy. The effects of target timing in INS on target acquisition (of both step and pursuit stimuli) were also investigated as an initial exploration of the INS dynamic characteristics. Incorporating the above INS properties to our OMS model, as well as simulating the mechanisms that determine the idiosyncratic gaze angle where the NAFX peak/nystagmus "null" (the field of gaze angles in which the NAFX is maximal) appears, had greatly expand the behavioral OMS by allowing simulations of more diverse variations of pathological conditions, and therefore greatly assist in our understanding of the OMS.