Internuclear ophthalmoplegia and contralateral exotropia Nonparalytic pontine exotropia and WEBINO syndrome

Abstract

To examine whether nonparalytic pontine exotropia, i.e., contralateral exotropia with internuclear ophthalmoplegia (INO), is caused by conjugate deviation by an ipsilateral paramedian pontine reticular formation (PPRF) lesion, we retrospectively reviewed seven patients with this disorder and two with wall-eyed bilateral INO (WEBINO) syndrome. In agreement with a hypothesis that this conjugate deviation is involved, one patient showed a transition from the paralytic to the nonparalytic form as the gaze palsy was resolved. Slowing of saccades toward the lesion was detected in another three patients. Unexpectedly, a milder outward deviation of the eye on the INO side was discovered during eye closure in three patients, implying the participation of a secondary deviation by fixating with the exotropic paretic eye. The presence of abduction nystagmus during fixation with the paretic eye supports this concept. In the two patients with WEBINO syndrome, deprivation of visual fixation with Frenzel goggles and eye closure similarly diminished exotropia, while one eye fixation elicited the marked outward deviation of the other eye with abduction nystagmus. In addition to conjugate deviation, therefore, our results show that secondary deviation induced by over-excitation of contralateral PPRF under fixation with the paretic eye is also involved in the development or aggravation of pontine exotropia.