internuclear ophthalmoplegia
Eye movement disorder caused by lesion in the medial longitudinal fasciculus, resulting in impaired adduction and horizontal nystagmus.
Full Definition
Internuclear ophthalmoplegia (INO) is a specific eye movement disorder caused by a lesion in the medial longitudinal fasciculus (MLF), the neural pathway that coordinates horizontal eye movements between the sixth and third cranial nerve nuclei. The characteristic finding is impaired or absent adduction of the affected eye during horizontal gaze, while abduction of the contralateral eye is preserved but often accompanied by horizontal nystagmus. The condition can be unilateral or bilateral and is commonly associated with multiple sclerosis in younger patients or brainstem stroke in older patients. INO significantly impairs smooth pursuit and saccadic eye movements, leading to diplopia and visual disturbance during horizontal gaze. The diagnosis is confirmed through clinical examination and may be supported by MRI showing MLF lesions.
Usage
Usage note: Often abbreviated as INO in clinical notes; ensure distinction from other ocular motility disorders.
In Context
- "Left internuclear ophthalmoplegia was evident with impaired left eye adduction and right eye nystagmus." — Examination findings
- "Bilateral internuclear ophthalmoplegia in this young patient suggests multiple sclerosis." — Clinical assessment