Objective: This study aimed to explore and compare visually-guided and memory-guided saccades in PD and MSA.

Background: Parkinson’s disease (PD) produced oculomotor alterations such as increased latency of visually guided saccades, reduced saccadic gain, impaired smooth pursuit and impaired inhibition of unwarranted reflexive saccades. Visually guided reflexive saccades are minimally impaired in PD, saccades to a remembered target are universally impaired, suggesting that structures in the basal ganglia may play a crucial role in the memory-guided voluntary saccadic pathway.

Method: We investigated visually guided reflexive and memory guided voluntary saccades by video-oculography in 19 PD and 11 MSA patients.  For visually guided saccades, each subject was instructed to fixate on a central red spot illuminated upon a black background. Just after the patient performed visually guided saccades, memory guided self-paced saccades tasks were tried. After removing the visual target, each subject was instructed to make the same fast eye movements for 60 s with an imaginary, remembered moving target.

Results: In both groups, voluntary saccadic velocity (194.25±59.39°/s in PD, 200.23±50.43°/s in MSA) was slower than reflexive saccade (243.09±36.88°/s in PD, MSA=244.04±48.5 4°/s in MSA). Reflective and voluntary saccadic accuracy were not significantly different in each patient group. Both PD and MSA patients showed longer pause during left eccentric position (PD=1514.12±467.91ms, MSA=1654.09±516.16ms) than during right eccentric position (PD=1418.25±495.03ms, MSA=1309.62±344.17ms).
During reflexive saccades, there was no difference of accuracy (26.79±1.95° in PD, 28.36±10.83° in MSA), velocity (243.09±36.88°/s in PD, 244.04±48.54°/s in MSA), and latency (258.88±55.93ms in PD, 294.85±68.58ms in MSA) between PD and MSA patients. During voluntary saccades, there was no statistical difference of accuracy (30.48±0.82° in PD, 24.13±7.47° in MSA), velocity (194.25±59.39°/s in PD, 200.23±50.43°/s in MSA), and pause (1466.18±474.71ms in PD, MSA=1481.87±392.49ms in MSA) between the patient groups.

Conclusion: In both PD and MSA patients, when compared to visually guided reflexive saccades, saccadic eye movements driven by memory guided voluntary effort had much slower velocity but preserved accuracy.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/voluntary-saccades-slowness-in-parkinson-disease-and-multiple-system-atrophy/