Fatiguing Saccades to Differentiate Ocular Motor Localization: A Pilot Study
Objective:
We propose a pilot study to differentiate neurologic disease based on ocular motor localization.
Background:
Eye movement pathways are widespread in the brain and offer inisghtful neurophysiological data. Studies have demonstrated the diagnostic and monitoring potential of saccadic eye movements tracking for various diseases. The distinct patterns of saccadic fatigue, due to cerebellar adaptation processes, can create specific eye tracking profiles that assist in distinguishing neuromuscular eye movement disorders from those originating centrally.
Design/Methods:
A portable monocular eye tracking system was utilized to gather and examine saccadic eye movements from n=5 subjects. A 3-laser saccade task introduces three stimuli with random variations in amplitude and direction, ranging 7.5° to 15° horizontally, both left and right. These stimuli facilitate the evaluation of various saccadic eye movement aspects.
Results:
The 5 subjects included one each of normal, vestibular neuritis, progressive supranuclear palsy (PSP), spinocerebellar ataxia type 2 (SCA2), and bilateral internuclear ophthalmoplegia. PSP and SCA2 showed reduced saccadic accuracy and velocity, with PSP having longer latencies (~400 sec) than SCA2 (~260 sec). In bilateral internuclear ophthalmoplegia, adduction saccade velocity (192°/s) was notably less than adduction (300°/s). Normal and peripheral vestibular neuritis subjects had standard saccadic measures. No saccadic fatigue was observed in all subjects after 2-minute repetitive task.
Conclusions:
In contrast to what observed in normal subjects and central eye movement disorders, we hypothesize that in ocular myasthenia gravis (OMG), saccadic accuracy changes with fatigue from repetitive stimuli, increasing with repetition count. This would provide the basis for differentiating OMG from non-neuromuscular junction cases.