[Diplopia in Wallenberg's syndrome]

The incidence and mechanism of diplopia were investigated in 31 patients with Wallenberg's syndrome resulting from acute dorsolateral medullary infarction. Diplopia was found in 10 of 31 patients (32%), with 5 patients reporting vertical diplopia alone and 5 reporting vertical and horizontal diplopia. Diplopia in Wallenberg's syndrome is considered to be caused by a lesion involving the otolith-ocular system. Vertical diplopia is simply explained by ocular skew deviation due to a lesion involving the vestibular nucleus; in which the affected eye becomes deviated inferiorly. In this situation, rotation of the eye due to ocular tilt reaction also occurs. Concomitant horizontal diplopia may require involvement of the medial longitudinal fasciculus (MLF), which produces skew deviation in mirror image; the unaffected eye becomes deviated inferiorly. When downward deviation of the eye affected by dysfunction of the vestibular nucleus and that due to MLF dysfunction affecting the other eye are comparable, only horizontal diplopia becomes apparent. MLF syndrome may be accompanied by paralytic pontine exotropia (PPE) or non-paralytic pontine exotropia (NPPE), both of which may also participate in the appearance of horizontal diplopia.