<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 palsylnternuclear ophthalmoplegiaDuanes reactionary syndromeAbsence of medial rectus muscle  <response>: Internuclear ophthalmoplegia. In this condition, there is lesion in the medial longitudinal fasiculus MLF. There is defective action of medial rectus on the side of lesion. Medial rectus causes adduction of the eye on same side. Contraction of right lateral rectus and left medial rectus causes Dextroversion whereas contraction of left lateral rectus and right medial rectus causes Levoversion. Horizontal nystagmus of opposite convergence is normal. Ref; A.K.Khurana;6th Edition; Page no: 355 