| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (HHC) Class of 2020, Baylor College of Medicine, Houston, Texas |
| Transcript |
Today we're gonna be talking about PION-- posterior ischemic optic neuropathy. The P is for posterior because what we're posterior to is the lamina cribrosa. The lamina cribosa separates the eye, the intraocular portion from the extraocular portion. And so normally, when we have ischemia of the optic nerve, it's anterior to the lamina cribosa. And that means we can see the disc edema. So the normal ischemic optic neuropathy (ION, ischemic optic neuropathy) is anterior ischemic optic neuropathy. The anterior means we are anterior to the lamina cribosa. And the most common cause of anterior ischemic optic neuropathy is nonarteritic anterior ischemic optic neuropathy. So an acute unilateral loss of vision in an elderly patient with vasculopathic risk factors and a RAPD and a swollen disk is very likely to be nonarteritic anterior ischemic optic neuropathy. But in every patient who has anterior ischemic optic neuropathy, we want to make sure that it's not arteritic ischemic optic neuropathy, and that's AAION. However, in PION, there is no disc edema. And there's no disc edema because the problem is posterior to this lamina cribosa. And that we call PION. PION is a diagnosis of exclusion, because you need to rule out other retrobulbar optic neuropathies, including retrobulbar optic neuritis, MS mimics like neuromyelitis optica, MOG-myelin oligodendrocytic glycoprotein, sarcoidosis-anything could be affecting this optic nerve, behind the lamina cribosa. So PION is a diagnosis of exclusion, so that normally we had to have a MRI scan: head, orbit, gadolinium, fat suppression, make sure that there's no enhancement of the optic nerve, this is just an optic neuritis or compressive lesion and they have to have some risk factors. The most common risk factors for PION are giant cell arteritis, so you could have arteritic PION, APION, arteritic posterior ischemic optic neuropathy. Or you can have not giant cell arteritis, and that not giant cell arteritis is nonarteritic posterior ischemic optic neuropathy. The nonarteritic posterior ischemic optic neuropathy, not giant cell can be from no cause, or can be from surgery. But not ocular surgeries, general surgical procedures including spine surgery and cardiac surgery where we have blood loss, hypotension and other risk factors including patient positioning that could lead to an ischemic event in the optic nerve that is retrobulbar. In some of those cases, MRI shows diffusion-weighted imaging abnormalities, indicating the ischemia at the level of the posterior optic nerve. So in summary, when you're confronted with a unilateral acute optic neuropathy or bilateral acute retrobulbar optic neuropathy, we must consider ischemia in the differential diagnosis, usually the ischemia is anterior called AION, of the nonarteritic or arteritic form. But sometimes the disc is not swollen, we call that PION, posterior ischemic optic neuropathy. Over time, the nerve will turn pale. And you should be thinking about GCA, giant cell arteritis, in every patient with PION who's elderly, but it might not be GCA and the most common not GCA form of PION, the nonarteritic form of posterior optic neuropathy is from general surgical procedures, usually spine surgery or cardiac surgery. But because it's a diagnosis of exclusion you need to do an MRI and the usual laboratory and other tests to make sure it's not some other optic neuropathy before diagnosing PION. |
