A model-based study of internuclear ophthalmoparesis and ocular-motor fatigue in multiple sclerosis.

Internuclear ophthalmoparesis (INO) in multiple sclerosis (MS) is due to demyelination of the medial longitudinal fasciculus (MLF). INO is typically modeled as an increased peak-velocity and peak-acceleration ratio of abducting to adducting eye (pulse-size ratio, PSR). PSR can be affected by fatigue during prolonged ocular-motor tasks (ocular-motor fatigue).

Improvement of internuclear ophthalmoparesis in multiple sclerosis with dalfampridine.

Internuclear ophthalmoparesis (INO) in multiple sclerosis (MS) is due to demyelination of the medial longitudinal fasciculus (MLF) and provides an accessible model for studying consequences of raised body temperature and fatigue on central demyelination. Prompted by one of our patient’s report of vision improvement after initiating dalfampridine, a potassium channel blocker prescribed for gait impairment, we measured this drug's effects on 3 patients with MS with bilateral INO. All showed changes in horizontal saccadic conjugacy consistent with improved transmission of the neural pulse responsible for adducting movements.