Internuclear ophthalmoplegia results from a lesion in the MLF: In young people, commonly caused by multiple sclerosis and often bilateral In older people, typically caused by stroke and is unilateral Rarely, the cause is Arnold-Chiari malformation, neurosyphilis, Lyme disease, tumor, head trauma, nutritional disorders (eg, Wernicke encephalopathy, pernicious anemia), or drug intoxication (eg, with tricyclic antidepressants, phenothiazines, or opioids).