| Identifier |
Alexanders_Law_1080p |
| Title |
Alexander's Law |
| Creator |
Andrew G. Lee, MD; Sydney Wendt |
| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (SW) Class of 2022, Baylor College of Medicine, Houston, Texas |
| Subject |
Alexander's Law; Nystagmus |
| Description |
Dr. Lee lectures medical students on the subject of Alexander's Law. |
| Transcript |
I want to tell you about a clinical law that we use, which is Alexander's Law. We use this in nystagmus, and it's useful because it tells you the direction in which the nystagmus is going to be worse. So even though we name nystagmus for the fast phase, so for example, downbeat nystagmus is going to be fast phase down, it's actually the slow phase that is the pathologic portion of the nystagmus. So it's the slow drift upward that is pathologic. The downbeat is a corrective saccade to get the fovea back on the target. And so, when we look in a patient for example who has downbeat nystagmus, you know that the paramedian tract in the brainstem has to talk to the cerebellum. And the part of the cerebellum that is involved in this fine motor control is the cerebellar flocculus. And in the flocculus, you have the granular cell and the Purkinje cell in the cerebellum. This Purkinje cell is going to talk to the superior vestibular nucleus that is also receiving innervation from your ear, but not the hearing part of your ear, the vestibular portion of your ear. But in this case, the signal has been disrupted from the supranuclear component. So this is a central vestibulopathy. So we have a central problem, either in your brainstem or your cerebellum that is causing this signal to be abnormal. This is an inhibitory signal, so it will lead to the superior vestibular nucleus stimulating when its not supposed to. And that means the superior rectus muscle is going to fire, and the eye is going to go up. That pathologic slow up phase must be compensated for by a compensatory downbeat nystagmus to keep the eye on the target. And so, when we have a downbeat nystagmus causing a slow pathologic up phase, the fast component is going to be carrying the eye back down.So for Alexander's law what that means is that if you're looking down, the eye will drift up and then you'll have to compensate with a downbeat nystagmus. And it's the same for upbeat in upgaze, and lateral in lateral gaze. If you are looking in the direction where the problem is, it will be worse. And that's kind of the general rule for everything. If you have a 6thnerve palsy,the double vision is going to be worse if you look in the direction of the 6thnerve palsy. And that's kind of the same thing for nystagmus. You'll be worse in the direction where the weakness is. And because the problem here is the slow pathologic drift up, it will be worse in downgaze. And that is Alexander's Law |
| Date |
2021-06 |
| Language |
eng |
| Format |
video/mp4 |
| Type |
Image/MovingImage |
| Collection |
Neuro-Ophthalmology Virtual Education Library: Andrew G. Lee Collection: https://novel.utah.edu/Lee/ |
| Publisher |
North American Neuro-Ophthalmology Society |
| Holding Institution |
Spencer S. Eccles Health Sciences Library, University of Utah |
| Rights Management |
Copyright 2019. For further information regarding the rights to this collection, please visit: https://NOVEL.utah.edu/about/copyright |
| ARK |
ark:/87278/s6228thh |
| Setname |
ehsl_novel_lee |
| ID |
1701552 |
| Reference URL |
https://collections.lib.utah.edu/ark:/87278/s6228thh |
