 AB ducting nystagmus are a variety of dissociated nystagmus, usually seen as part of an inter-nuclear ophthalmoplegia. This patient has a subtle inter-nuclear ophthalmoplegia. What's most evident is a dissociated nystagmus. The right eye has right-beating, jerk nystagmus. Smaller oscillations can be seen in the left eye. An inter-nuclear ophthalmoplegia localizes to an intrinsic lesion of the brainstem.