(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (DR) Class of 2023, Baylor College of Medicine, Houston, Texas
Subject
Optic Neuropathy; Giant Cell Arteritis; Ischemia
Description
Dr. Lee lectures medical students on the subject of cupping in AION.
Transcript
"Okay so today I'm going to be talking a little bit about cupping in AION. And as you know there are two types of AION (Anterior Ischemic Optic Neuropathy). There's the non-arteritic form of AION and there's the arteritic form of AION, which of course means giant cell arteritis. And so when we're trying to differentiate NAION, the non-arteritic form of anterior ischemic optic neuropathy from AAION, the arteritic form of anterior ischemic optic neuropathy, one of the clues is cupping. And so normally for the non-arteritic form of AION the cup-to-disc ratio is a small cup-to-disc ratio. And that's because there's probably some structural risk factor for having edema localized in the disc head and that localized edema in a small crowded space can lead to a vicious cycle of further ischemia. And that is one of the pathogenic mechanisms that is presumed to be underlying the non-arteritic form of anterior ischemic optic neuropathy. And so if we see a big cup in a patient who has AION, you really should be thinking that it might be arteritic anterior ischemic optic neuropathy. So the big cup-to-disc ratio in the fellow eye is a clue that we might be dealing with giant cell arteritis. The other way the cupping comes to us is if a patient has disc edema but especially pallid edema, and then gets the cupping after the event. That's also a sign that it's arteritic. And the reason is, as you know from glaucoma, the ophthalmoscopic feature of glaucoma is cupping. And so the pressure is pushing down on the level of the lamina cribrosa and that force causes mechanical deformation in the nerve head itself which we can see as ophthalmoscopic cupping. But in typical glaucoma it's a mechanical intraocular pressure related thing. As opposed to non-arteritic anterior ischemic optic neuropathy which damages the axon but really only produces pallor. So the non-arteritic form of anterior ischemic optic neuropathy usually leads to sector or diffuse optic atrophy without the cupping. However in patients who have giant cell arteritis, the damage is much more expensive so if someone has pallid edema they have ischemic infarction which is going to kill not only the axon and cause the pallor but knock out the support cells and the trabecular beams that normally are supporting the lamina cribrosa. And so we can get the cupping again even without elevated intraocular pressure if you destroy the underlying trabecular beams that are the support structure of the lamina cribrosa. So cupping before or cupping after anterior ischemic optic neuropathy should suggest that it is the arteritic form of AION and that's giant cell arteritis."
