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F.A. Proudlock, C.M. Knapp, R. Abbott, Y. Rajabally, I. Gottlob; Vertical Optokinetic Nystagmus and Smooth Pursuit in Parkinson’s Disease . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2659.
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© ARVO (1962-2015); The Authors (2016-present)
Several oculomotor deficits have been described for Parkinson’s disease (PD) including hypometric saccades, impaired smooth pursuit initiation and decreased ability of making saccades to remembered or predicted target locations, however, little is known about vertical OKN. We have investigated horizontal and vertical OKN in PD patients comparing smooth pursuit and other eye movements.
Eye movements were recorded in 15 PD patients and 15 aged–matched controls while performing vertical and horizontal OKN (at 20°/s and 40°/s using 50x60° field), smooth pursuit (linear velocity at 20°/s and 40°/s) and a saccadic task (10° and 20° centrifugal and centripetal steps). Slow phase gains and beat frequencies measured during OKN were compared to other tasks.
PD patients showed a consistent vertical asymmetry for OKN gain with preference for upwards moving stimuli at 20°/s (p=0.02) and 40°/s (p=0.003). The same pattern was observed in pursuit gain more obviously at 40°/s (p<0.001) than at 20°/s (p=0.18). In contrast, vertical asymmetries of OKN gain were not significant in aged–matched controls at either stimulus velocity. Vertical asymmetries of OKN gain were correlated to vertical asymmetries of pursuit gain at 20°/s (p<0.001) and 40°/s (p=0.01). There were no vertical asymmetries in beat frequency.
There are significant asymmetries in vertical OKN and pursuit gain in PD patients, particularly at faster stimulus velocities, with preference for upwards moving stimuli. A possible explanation could be neurodegeneration of cerebellar neurons. This finding may prove to be useful for diagnostic purposes.
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