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P.A. Wetzel, E.L. Mallahan, V.P. Calabrese, W.L. Felton; Effects of Parkinson's Disease and Severity on Fixation Stability . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2931.
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Purpose: Parkinson’s disease (PD) is a progressive neurological movement disorder. Beyond the outward symptoms of PD, many report difficulty with tasks that require visual stability. In PD, stabilization of eye movements during fixation is not well understood but is critical to the acquisition of visual information. The purpose of this study was to investigate eye and head movement differences between PD patients and age–matched controls during fixation and other visually related tasks. Eye position measurement has the potential to provide a quantitative method for early diagnosis and assessment of PD. Methods: Eye and head movements of PD patients (N = 33) and similar age–matched controls (N = 15) were recorded while performing simple fixation tasks, smooth pursuit and compensatory movements. All participants were neurologically examined immediately before recording and assigned a clinical measurement of disease severity based on the motor section of the Unified Parkinson’s Disease Rating Score (UPDRS). Patient ages ranged from 53 to 83 (controls 65 to 79) years. Participants were instructed to fixate on horizontally and vertically spaced targets located at 0°, ±5° and ±10° and to perform additional pursuit and compensatory tracking tasks while unrestricted eye and head movements were recorded at 120 Hz using a six–degree of freedom magnetic head tracker and a two–dimensional eye measurement system. Data were analyzed for positional stability and absolute velocity of movement during fixation and were correlated to the UPDRS assessment. Results: Unstable, non–rhythmic eye movement behavior even in patients with mild disease severity and no outward visible signs of tremor in any part of the body were observed. Absolute velocity of eye movement and positional variance were significantly greater than the control group and appear to increase with UPDRS assessment. Those with more advanced disease severity showed development of an additional directionally specific, episodic component of rhythmic eye tremor. Conclusions: PD appears to disrupt the normal stability of eye movements, which become increasingly destabilized with disease progression and precede the development of rhythmic tremor. A more complete understanding of eye movement behavior during fixation can potentially provide an objective method for early clinical diagnosis, assessment and treatment of PD.
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