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P.A. Wetzel, W.L. Felton, III, K.L. Holloway, R.T. Seel, M. Haselman, N. Eubank; Effect of Deep Brain Stimulation on Eye and Head Movements in Parkinson’s Disease . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1935.
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Purpose: Parkinson disease (PD) is a progressive neurological movement disorder caused by degeneration of dopaminergic cells in the substantia nigra resulting in hypokinesias, rigidity and tremor. Current pharmacological treatments either increase the level of dopamine or decrease the level of acetylcholine production in the brain. As the disease progresses, these medications often become less effective and surgical procedures may be considered which include Pallidotomy, Thalamotomy and more recently, Deep Brain Stimulation (DBS). The stimulating electrode is surgically implanted within the globus pallidus or in the ventrointermediate nucleus of the thalamus which is then stimulated by a continuous train of high frequency current pulses from the DBS module. The module can be programmed to minimize tremor or can be turned on or off by magnet. When the device is off, the disease symptoms return within minutes to a level similar to the pre-surgical condition. To investigate the influence of DBS, we analyzed the eye and head movements of PD patients for simple tracking tasks. Methods: Over the course of several months the eye and head movements of several PD patients with unilateral and bilateral stimulators were recorded. Patients were evaluated either before surgery or as early as one week after surgical implantation of the DBS device and then at roughly one-month intervals thereafter. Patients performed fixation and vertical and horizontal visual tracking tasks while unrestricted eye and head movements were measured at 120 Hz using a magnetic head and a two-dimensional eye measurement systems. Data were analyzed for position, velocity, amplitude, saccadic duration and coordinated gaze control. Results: Differences in eye and head movement control were observed as a function of the evaluation interval and DBS device adjustment. Fixation stability was notably improved however, several patients showed abnormally long saccadic durations. Episodes of tremor affecting eye, head or both were observed during fixation and pursuit tasks with amplitudes of 3° or greater and frequencies up to 7.8 Hz. Conclusions: The normal coordinated relationship between eye and head movement appears to be adversely affected by PD. DBS can minimize but not eliminate episodes of tremor but may also affect the dynamic behavior of eye movements.
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