<prompt> A patient presents with diplopia with limitations of adduction in the left eye and abducting saccade in the right eye. Convergence is preserved. Most likely etiology is:Paial 3rd nerve palsyInternuclear ophthalmoplegiaDuanes reactionary syndromeAbsence of medial rectus muscle  <response>: B. i.e. Internuclear opthalmoplegia In type III internuclear opthalmoplegia, none of the eyes abduct completely while the adduction is complete Le. normal convergenceQ. Dissociated Opthalmoplegia There is dissociation in gaze movements i.e. one eye moves in one direction whereas the other eye cannot move in the same direction. Internuclear Opthalmoplegia INO Medial longitudinal Fasciculus MLF connects 3rd and 6th nerve nuclei. A lesion in MLF produces INO and prevents harmonious coordination of these nuclei in producing conjugate both eye moving in same direction movements. Etiologies may be Unilateral Bilateral - Vascular lesion or infarct of small branch - Multiple sclerosis m.imp of basilar aery m.imp - Neoplasm - Brain stem tumors - Inflammation - Multiple sclerosis - Myasthenia gravis - Myasthenia gravis - Occlusive vascular disease - Cryptococcosis 