Think superior oblique palsy.

Superior oblique palsy is thought to be the most frequent cause of acquired vertical diplopia. It is often the result of blunt head trauma but may also be caused by brain tumor, meningitis, diabetes, lesions of the cavernous sinus, and superior orbital fissure as well as arteriosclerosis. The characteristics frequently include a small vertical strabismus in primary gaze, ipsilateral inferior oblique overaction with an increased hypertropia to the contralateral side, a "V" pattern, excyclotorsion, and a positive Bielschowsky head tilt test to the ipsilateral side. In a typical case, it is not difficult to make the proper diagnosis. Several patients will be described whose superior oblique palsy was marked by an association with another motility disturbance.