Objective: To assess the effect of dopaminergic medication on eye movements in Parkinson’s disease (PD).

Background: PD is the second most common neurodegenerative disease, characterised by brady-hypokinesia, resting tremor, rigidity, and balance impairments. Other abnormalities, such as changes in eye-movements, also occur. Treatment is based on dopaminergic therapy. The effect of dopaminergic medication on eye-movements is however not clear.

Method: 21 healthy subjects (HS) and 20 PD patients, all of whom were tested on medication (PD-ON); 17 of them were also tested off medication (PD-OFF). The motor condition of the patients was assessed with Movement Disorders Society – Unified Parkinson’s Disease rating Scale part III (MDS-UPDRS part III). Reflexive saccades, antisaccades, and smooth pursuit with three different velocities of the moving target (low, medium, and high) in horizontal and vertical plane were evaluated with an eye-tracking system.

Results: Compared to HS, PD-ON showed greater latency in horizontal smooth pursuit tasks when the target was moving at high (p=0.004) and medium (p=0.043) velocities. Compared to HS, PD-ON (p=0.010) and PD-OFF (p=0.017) were less accurate in tracking the target moving with high velocity in the vertical direction. PD-OFF had greater latency in vertical smooth pursuit at medium target velocity compared to their latency ON medication (p=0.035) as well as compared to HS (p=0.022). PD-OFF needed more time to perform antisaccades compared to PD-ON (p=0.044). Expectedly, the overall MDS-UPDRS part III was higher off medication than on medication (p=0.038).

Conclusion: Compared to HS, patients with PD had prolonged latencies in horizontal and vertical smooth pursuit. Similarly, PD patients were less accurate in vertical smooth pursuit. Dopaminergic medication affected the latency of vertical smooth pursuit and the time needed to perform antisaccades. There were no significant differences in the latency of reflexive saccades and in the number of errors in antisaccades between the groups.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/differential-effect-of-dopaminergic-medication-on-smooth-pursuit-vs-saccadic-eye-movements-parkinsons-disease/