To investigate diagnostic accuracy in identifying saccadic slowing. 

Saccades are rapid eye movements with which the visual world is explored. Saccadic slowing is pathologic, key to neurological diagnosis, and often correlated with disease severity. There is currently no universally accepted standard for the definition of saccadic slowing, and inter- and intra-rater reliability is unknown.

Patients with slow saccades and control participants with eye movement videos and quantified eye tracking (Eyelink) were identified. Quantified saccade data were categorized as normal versus mildly/moderately/severely slow by blinded expert review (JRR, TEH, JCR) of main sequence relationships (peak velocity to amplitude). We compiled 24 de-identified, brief looped clips showing horizontal or vertical saccades. Videos were randomized and placed in a slideshow. Subsequently, clinicians, stratified by expertise level, reviewed the videos for saccadic slowing and, if present, graded the degree as mild, moderate, or severe. Clinician responses were compared to main sequence analysis categorization.

Nine patients (7 PSP, 1 genetic parkinsonism, 1 SCA2) and 3 control participants were included. Ten clinicians were recruited; five senior neurology residents (PGY-3-4) and five general neurology attending physicians. For saccades deemed normal as per recordings, 51% of general neurology attendings and 58% of senior residents judged saccadic velocities as normal. Horizontal and vertical saccades were, respectively, accurately judged as normal 60% versus 40-50% of the time. For saccades deemed abnormal as per recordings, 81% of general neurology attendings and 87% of senior neurology residents judged saccadic velocities as slow. Horizontal and vertical saccades were, respectively, accurately judged as slow 68-77% versus 94-97% of the time.

Clinicians showed greater capacity to identify saccadic slowing, especially vertically, than to confirm normal saccadic speed. Horizontal saccades were more easily identified as normal than vertical saccades. Identification of normal and abnormal saccades was largely unaffected by experience level.