(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (JEL) Baylor College of Medicine, Houston, Texas
Subject
Movements; PPRF Vestibulo-ocular
Description
Dr. Lee lectures medical students on the subject of roving eye movements.
Transcript
So today I want to talk to you about roving eye movements, which is something that someone requested, so if you have something that you want us to make a video on please request it in the comments section and we'll look at it. So the question to me was what is the significance of roving eye movements in a patient who is in coma. And the second part of the question was why do they occur. So when we have coma, that could be supratentorial or it could be infratentorial. And so when we have eye movements that are roving, both eyes are moving, we have conjugate or disconjugate movements which means they are moving in the same direction or moving in opposite directions, and normally it's horizontal movement. And the reason that's important is patients whose eyes cannot move: that usually means that you have deficits in the infranuclear pathway and so that's going to be the cranial nerve nuclei 3 4 and 6. So if the eyes don't move at all then we can use the doll's head maneuver to see if we can stimulate the eyes to move by using the ear but not the hearing part of your ear but the vestibular part of your ear. So when you have the doll's head maneuver you are enacting the vestibulo-ocular reflex, and if so the if the problem is supranuclear the eyes will move. If the lesion is nuclear or infra-nuclear, then stimulating it with the doll's head maneuver won't make the eyes move. And so the doll's head maneuver is one of the important tests that we're using in patients who are comatose to see if the lesion is supranuclear or infranuclear. And that's the same kind of thing that the roving eye movements tell you because the eyes are moving and that means the eyes can move so if the eyes are moving that means the eyes can move which means we're probably dealing with a supratentorial cause of the coma like hypoglycemia or seizure or something in the cortex that is causing this and not something in the brainstem like a locked-in brainstem stroke or something of that nature at the brainstem level. And so when we're dealing with roving eye movements in a comatose patient that actually might be good because it means their eyes can move. The second part of the question was why is ithorizontal. And that is a more interesting question-it probably could theoretically be vertical however the horizontal nature of the eye movement is because we have both stimulatory and inhibitory signals coming from the brainstem. And so the brainstem driver is parapontine reticular formation in the pons and that's the driver for these horizontal movements. A horizontal scanning movement and so if you disconnect the top, the supernuclear input, when you are in coma, then this driver will start to tell the eyes to move. And that happens when you go to sleep. So when we go to sleep we have rapid eye movements (REM)and you can see that under the closed lids in people who are entering in this sleep the REM(REM)sleep their eyes are moving back and forth horizontally. It's not clear what the purpose of rem is for sleep but some people believe that you're actually visualizing your dream, that you're actually looking around to see, and so it's not really roving you're actually watching your dream. It's not clear whether that's true or not, it probably doesn't matter. But it is interesting that the REM movement and the roving eye movement of coma indicates firing of the pontine parapontine reticular formation to make your eyes go side to side and that probably means that whatever is making you asleep, whether it's the coma or the regular sleep, is super tentorial. And this is the significance of those roving eye movements.
