In a series of 72 cases of internuclear ophthalmoplegia, 12 of 41 bilateral lesions were associated with occlusive cerebrovascular disease. Two were verified pathologically.
This frequency is more in keeping with the pathologic substrate of brain stem infarction in general, and of those with medial longitudinal fasciculus (MLF) involvement in particular, than has been acknowledged previously.
Convergence, abducting nystagmus, and tropias were not reliable in differentiating midbrain and pontine involvement. Bilateral vascular involvement is frequently associated with at least transient impairment of consciousness. Associated horizontal conjugate gaze paralysis occurred as often as in unilateral lesions. The "one-and-a-half syndrome" in a comatose patient suggests underlying bilateral MLF lesions.
While multiple sclerosis remains the leading cause of bilateral internuclear ophthalmoplegia, vascular lesions are not uncommon.
Edward F. Gonyea. Bilateral Internuclear OphthalmoplegiaAssociation With Occlusive Cerebrovascular Disease.. Arch Neurol. 1974;31(3):168–173. doi:10.1001/archneur.1974.00490390050004