Objective: To determine, in a very large sample, how different types of eye movement are differentially impaired in early manifest HD, and determine whether vertical or horizontal eye movements are the more affected.

Background: One of the earliest signs to appear in manifest Huntington’s disease (HD) is abnormality of eye movement. Vertical eye movements are reportedly affected earlier and to a greater extent than horizontal eye movements. These studies however are based on relatively small numbers of HD subjects and anecdotal observations have suggested that horizontal eye movements may be more impaired, at least in some.

Methods: Data from the clinical motor assessment component of the Unified Huntington’s Disease Rating Scale (UHDRS was obtained from the ENROLL-HD database, an international, prospective-cohort study, created for collation of HD information. We accessed the database, with permission, in December 2017. The annual motor assessment includes 6 oculomotor parameters: horizontal and vertical smooth pursuit, saccade latency, and saccade velocity, each graded in severity from 0-4. There were a total of 4752 manifest HD participants at the time of analysis with mean age of 59.2±12.6yrs and mean CAG repeat number of 44.1 ± 4.0.

Results: Impairment in all oculomotor parameters increased in a linear fashion over the first 8 years of manifest disease. Vertical smooth pursuit and saccade velocity scores at disease onset were greater (i.e. more impaired) than horizontal scores, by a small but significant extent, but there was no difference in the rate of increase of scores over time between the two directions. There was no difference between vertical and horizontal saccade latency scores at onset and over time.

Conclusions: Vertical eye movements, with the exception of saccadic latency, are affected to a slightly greater extent than horizontal movements, and all types worsen in a linear fashion over at least the first 8 years after disease onset.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/vertical-and-horizontal-eye-movements-in-a-large-cohort-of-early-manifest-huntingtons-disease-evidence-from-enroll-hd/