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PA Wetzel, A Habib, C Neering, WL Felton, M Haselman, KL Holloway; Effect of Parkinson’s Disease and Deep Brain Stimulation on Eye and Head Movements During Reading . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4671.
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Purpose: Parkinson's disease (PD) is a progressive movement disorder caused by degeneration of dopamingeric cells in the substantia nigra resulting in resting tremor, rigidity of movements, reduced motor and oculomotor control. As PD progresses, ineffectiveness or intolerance of medications may result in surgical implantation of a deep brain stimulus (DBS) electrode within the globus pallidus or the ventrointermediate nucleus of the thalamus to minimize tremor. To investigate one aspect of PD on quality of life, we analyzed the eye and head movements of patients with DBS devices while reading. Methods: Eye and head movement data from age matched non-PD and PD patients with unilateral and bilateral DBS implantable stimulators were measured during reading. A group of thirty-five text passages of roughly equal character length and ranked according to increasing difficulty from first grade level to the most difficult technical prose were used. Up to ten randomly selected passages were presented to each patient. A light box positioned 40 cm from the patient, provided back illumination of individual texts printed on transparency material during reading in an otherwise darkened room. The angular extent of each text passage was ±12° H by ±6° V. Patients were instructed to read for comprehension. Unrestricted head and eye movements were measured at 120 Hz using a six-degree of freedom magnetic head tracking system and a two-dimensional pupil-corneal reflection system. Stored eye and head position data were then analyzed for the number and duration of fixations, fixation stability, regressions, saccadic amplitude and overall gaze control. Results: Differences in eye and head movement during reading were observed between PD and control patients. PD patients on occasion showed episodes of tremor that reduced fixation stability. Periods of fixation instability were observed to be associated with uncompensated, uncorrelated movements of the eye and or the head. Conclusion: The use of DBS implantation devices can have a significant influence on minimizing tremor and on reducing random episodes or periods of uncompensated head and or eye movement during reading. These episodes can lead to an inability to adequately stabilize fixation resulting in greater reading difficulty and reduced overall quality of life.
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