Objective: Our research utilizes the technique of brief linear smooth pursuit of a moving target, to derive various parameters. These parameters are then analyzed to identify differences from a control group and to examine their relationship with the severity of cerebellar ataxia (CA).

Background: There is a need for measures that are clinically significant and capable of monitoring the severity and progression CA. Quantitative oculomotor measures might offer a straightforward, dependable, and sensitive biomarker for CA.

Method: 30 CA patients with different degrees of impairment and age-matched controls were tested in two short experiments. We recorded eye movements while the participant followed a white disk moving from the center outwards in straight lines in different directions in random order. We developed 6 oculomotor indices to assess the quality of tracking: (1)“Saccadic pursuit” (the saccadic contribution to tracking), (2)Pupil dilation (start of tracking), (3)Initial saccade latency (open-loop phase), (4)Occluder-induced deviation from un-occluded tracking, (5)Vergence stability (the STD of the lag between the eyes during tracking), and (6)pre-stimulus saccadic inhibition. We investigated the differences between groups in these indices and the correlation of the oculomotor indices with the clinical assessment.

Results: We found a significant deficiency in 3 of the oculomotor indices in CA patients compared to controls. Notably, for smooth tracking that requires a tight closed-loop process, the patients were slow to start, applied less anticipatory microsaccade inhibition, used excessive catchup saccades, were inefficient in keeping vergence, and did poorly in coping with occlusion. All 6 indices were significantly correlated with the Scale for the assessment and rating of ataxia score (SARA), with R=0.4-0.7;p<0.005. Notably, the oculomotor abnormalities included reduced anticipatory inhibition of movement.

Conclusion: The findings reveal a notable abnormality in simple visual tracking among patients with CA, highlighted by deficiencies in six distinct oculomotor indices. These indices, which reflect both eye movement and inhibition characteristics, show a correlation with CA severity, suggesting their potential as quantitative biomarkers for evaluating treatment effectiveness. Further investigation is required to fully assess this possibility.

References: Garces P. et al., “Quantitative Oculomotor Assessment in Hereditary Ataxia: Discriminatory Power, Correlation with Severity Measures, and Recommended Parameters for Specific Genotypes” Cerebellum, 2024 Feb;23(1):121-135.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/oculomotor-biomarkers-for-cerebellar-ataxia-and-severity-in-smooth-pursuit/