| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (JS) Class of 2021, Baylor College of Medicine, Houston, Texas |
| Transcript |
Today we're going to be talk about nystagmus. Nystagmus means nod, so it's kind of a nod you get when you're falling asleep and then your head goes back. We don't have time to show all the forms of nystagmus, so we're only going to talk about the localizing forms. For our localizing forms of nystagmus, that tell you where the lesion is, and there are non-localizing forms of nystagmus, which do not tell you where the lesion is. The non-localizing forms of nystagmus are way more common. They're like gaze-evoke nystagmus but in primary position, there are localizing nystagmus. So all the gaze of "loc" nystagmus, a beaten-up up gaze, down beaten down gaze, horizontal jerk being established - those don't localize at all. The localizing ones depend on the waveform. The more morphology, what you see of the nystagmus. So we're just going to cover the ones that are localized. As you know, we named a nystagmus for the fast phase; so a down-beat beats down- a slow phase up followed by a downbeat fast phase - so slow and fast. So the fast phase and down made is towards down. It'll also be worse when you look down - that's Alexander's law. So downbeat nystagmus localizes to cervical medullary junction and even though downbeat can be seen in other posterior fossa lesions, I'm only showing you the most common localizations. Downbeat = cervical medullary junction, C. Upbeat, the fast phase is going up (in primary position, not gaze above) = usually localizes to the vermis of the cerebellum, although it can be in the posterior fossa, including the medulla. Upbeat - U, Vermis - V. Then we have convergence - retraction nystagmus. It's not really a nystagmus, it's a nystagmoid movement so the eyes converge and then retract because we have co-firing of all the muscles of III. The medial rectus makes it converge, and if you fire the superior and inferior rectus at the same time, it retracts the globe. So convergence and retraction nystagmus. C = the dorsal midbrain. D = dorsal midbrain. C = converge retraction nystagmus. Then we have See-Saw nystagmus, which looks like a see-saw. So, one eye is going up and then there will be torsion and the other eye's doing the exact opposite. So, it's like a see-saw. This see-saw nystagmus, S, localizes to the third ventricular area, or the parasellar region. See-saw, S, third ventricular parasellar region, T. There are also some cerebellar nystagmus that localize that don't match up with the letters. So, rebound and periodic alternating nystagmus and the Bruns Cushing nystagmus. The Bruns Cushing actually does match up because the Bruns Cushing, B, matches the cerebellopontine angle, CPA. And the most common causes of acoustic neuroma. Rebound looks like periodic alternating nystagmus except it's gaze-evoked. So periodic alternating nystagmus - first, it's going to be horizontal jerking to the left, then it'll slow down, do nothing, and then it'll beat to the right. It alternates, periodically. It can be acquired or congenital. The acquired form localizes to the cerebellum and Baclofen is the treatment. Rebound is like periodic alternating nystagmus; it beats horizontal jerk in one direction and you come back to the center and then it starts beating to the other direction. As opposed to the periodic alternating nystagmus which alternating with periodicity, rebound is evoked by gaze. So it's like a basketball, it hits the board and rebounds back. So the basketball hits, gaze evoked to the left. Comes back to primary. Then starts beating rebound to the right that is also a cerebellar form of nystagmus. Bruns Cushing nystagmus is a gaze evoked nystagmus and a gaze paretic nystagmus. So we got a larger amplitude, slower frequency on gaze to the right, and a gaze invoked higher frequency, smaller amplitude nystagmus on gaze to the left. The combination of gaze evoked and gaze paretic nystagmus, we call the Bruns Cushing Nystagmus, and that localized to the cerebellopontine angle. All the other forms of nystagmus are kind of not localizing. MRI, posterior fossa, drugs, toxins - that's what you should be thinking about. So in terms of localization, we really should be thinking of downbeat, upbeat, convergence-retraction, see-saw, rebound, periodic alternating nystagmus, and the Bruns Cushing nystagmus. Everybody else is non-localizing. |
