Differentiation of internuclear ophthalmoplegia and myasthenic pseudo-internuclear ophthalmoplegia by subjective visual vertical

Objectives: Internuclear ophthalmoplegia (INO) is characterized by an adduction deficit on lateral gaze and a dissociated nystagmus of the abducting eye. In the majority of cases INO occurs with lesions of the medial longitudinal fascicle (MLF) caused by multiple sclerosis or ischemia. However, extraocular muscle weakness in myasthenia gravis (MG) can mimic this ocular motor pattern and has been referred to as pseudo-internuclear-ophthalmoplegia (pseudo-INO). Differentiation between these entities can be difficult but is crucial for choosing specific therapeutic strategies. We here report that measurement of the…