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Aasef Shaikh, Fatema Firoz Ghasia; Saccades in Parkinson’s disease: hypometric, slow, or maladaptive?. Invest. Ophthalmol. Vis. Sci. 2019;60(9):523.
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© ARVO (1962-2015); The Authors (2016-present)
Visuomotor impairments such as hypometria of visually guided saccades is common in Parkinson’s disease. Abnormal activity of the superior colliculus due to increased inhibition through excessive substantia nigra pars reticulata activity can cause abnormal saccades. Impaired preparatory phase in the frontal eye field as a consequence of abnormal tectal influence can also lead to saccade abnormality. Abnormal brainstem burst generators can also cause saccade dysfunction.
We measured ocular motor function in 20 PD patients using quantitative high-resolution oculography. Horizontal and vertical visually guided saccades were analyzed. The experiments addressed important dichotomy whether visually guided saccades in Parkinson’s disease reflect excessive inhibition of the superior colliculus or is due to an involvement of brainstem saccade generators.
We discovered unique properties of visually guided saccades in Parkinson’s disease. In addition to hypometria, we also discovered slowing, interruptions, and curvatures in the saccade trajectory. The curvature not only reflected the mismatch in the velocity of relatively slower vertical and faster horizontal saccades, but it was thought to be due to aberrant activation of the superior colliculus. The irregularities in the saccade trajectory and slowing was prominent in the vertical direction.
We suggest that abnormal saccades in Parkinson’s disease not only reflects abnormal tectal function, but also suggests abnormal oscillatory behavior in the reciprocally innervating circuit of excitatory and inhibitory burst neurons. Impaired function of excitatory and inhibitory burst neurons causing maladaptive feedback and premature activation of the superior colliculus can cause irregularity in saccade trajectory.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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