| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York |
| Transcript |
"So today we're going to be talking about the pupil in relation to something that ophthalmologists don't see in the clinic, obviously, but you might be called to the floor in a patient who is comatose. So we really got two types of pupil problems here. Problems when the pupil is a different size: "coria" is our pupil word, "iso" means same and "an" means not; so not the same size pupil. So we got a big one and a small one. Then the other way is when we have isochoric pupils that are the same size but they're still abnormal. So pupils can be normal or abnormal. They can be abnormal and isocoric or they can be abnormal and anisocoric (different size pupils). So when you're dealing with the big and the small pupil, the main considerations are am I dealing with a problem with the parasympathetic nervous system or am I dealing with a problem with the sympathetic nervous system? The sympathetic nervous system dilates your pupil and the parasympathetic constricts your pupil. This is mediated on the third nerve for the parasympathetic. And for the oculosympathetic pathway for the sympathetics, which is the Horner syndrome. And so one of the first things we're going to do in an anisocoria is determine: Am I dealing with the big pupil problem or a small pupil problem. We're going to test the light reaction and if the light reaction is poor (it doesn't constrict), then that's the bad pupil. If the light reaction is good in both eyes and the anisocoria is greater in the dark, that means it's not dilating properly, and that is a sympathetic lesion. So if it's a dilation problem in the dark with a normal light reaction (the anisocoria is greater in the dark), then that's Horner syndrome. And obviously patients who have a Horner syndrome and are comatose have a lesion somewhere disrupting the sympathetic pathway all the way from the hypothalamus down to the spinal cord. But usually that means they have a brain stem lesion, and so a bilateral or a unilateral Horner syndrome can occur in patients who have a structural lesion from being in comatose. Third nerve palsy is also a bad thing to see in a patient who has a coma, because anisocoria usually indicates that we have a parasympathetic problem in the third nerve. And the main concern here is that they're herniating. So the third nerve travels from the midbrain ventrally and then passes into the subarachnoid space. In that location, we can get a herniation syndrome because the tentorium is rigid and the third nerve runs right at that location and that is called Kernohan notch. So at the notch in the tentorium the cranial nerve number three passes and so it as you know in the NICU, the neurosurgical intensive care unit, the nurses are always checking the pupil. And what they're looking for is anisocoria. And a blown pupil from third nerve palsy is evidence that we might have a herniation syndrome and that person is obviously going to be an acute onset of their coma status and it's an emergency. That is what we call a false localizing sign because the herniation is super tentorial, but you see the pupil problem and that means the third nerve but it's from herniation of the brains uh down into the Kernohan notch. You could also have it bilaterally, and that is a very bad sign. So fixed and dilated pupils bilaterally: very bad sign in comatose patients. Be thinking about herniation syndromes. But those also could be lesions anywhere along the third nerve: that means the midbrain. And if we have isochoric pupils they can both be big or they can both be small. If they're both small, that's pinpoint pontine pupil, so that normally means something's wrong with the pons. If it's big and bilateral isocoric, that usually means midbrain pupils. Both are bad. So these are brainstem signs that we should be looking for. The last thing you should be aware of is sometimes people have anisocoria because it's pharmacologic, but usually it's by accident. The most common thing that we see is scopolamine, which is usually a patch that's put behind their ear to reduce the nausea and then some unsuspecting nurse or family member or even the patient themselves if they're not comatose touches their eye, they get a blown pupil. It'll get mistaken for the Kernohan notch. And also the inhalers. The most common is the atropine based inhalers: ipitropium bromide atrovent. The atrovent inhaler has atropine and that'll dilate your pupil if the inhaler is blasting your eye instead of blasting your nose. So in summary if you've got a pupil abnormality and your comatose, it's a bad sign. We'd like to make sure it's not pharmacologically dilated, because that might lead to inappropriate interventions. However, if it's a big pupil the anisocoria is going to be greater in the light. If it's a small pupil problem, greater in the dark. The light problem is parasympathetics, that's third nerve. And the Horner syndrome for the dark. If it's isocoric and poorly reactive, that's pinpoint pontine pupils. They often have spastic tetraparesis and hyperreflexia. If, however, it's isochoric and big pupils, that's usually a midbrain problem - third nerve, again. And you should be worried about the false localizing sign, the herniation sign, the Kernohan notch phenomenon, in a patient who's acute comatose." |
