| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (EL) Class of 2023, Baylor College of Medicine, Houston, Texas |
| Transcript |
So today we're going to try to differentiate glaucoma vision loss from not glaucoma, but in particular, neuron causes of not glaucoma. So normally when you have glaucoma, we see a distinctive ophthalmoscopic finding which is called cupping. As you know the optic nerve is like a doughnut and so the rim is like the doughnut and the hole of the doughnut is like the cup. And so, if we have a nerve that's cooked out, we have lost nervous tissue and that cupping is the distinctive ophthalmoscopic finding of glaucoma. In glaucoma, the patients typically lose their visual field and the reason is pressure related phenomenon normally affect the longer fibers first and so we have fibers that travel from the superior temporal and inferior temporal part of the fundus and instead of going straight across, like this, they go on an arc all the way around to avoid crossing through the fovea. So, these fibers travel to the top and the bottom of the disc. Because the fovea is actually the center of the eye, that means these fibers here are nasal and these fibers also are nasal and the whole optic disc is actually nasal. So, when we're looking at nerve fiber layer loss, we're trying to determine if the nerve fiber that is damaged is the temporal fiber, which is up and down like an hourglass, or the nasal fiber which is side to side like a band or a bowtie. And so in glaucoma, because it's the temporal fiber that is usually damaged because it is a very long course, then it's going to respect the horizontal meridian when we have a visual field, it's going to arc around, and because it's a temporal fiber that's damaged, it's usually going to produce a visual field defect that's nasal. So the most common visual field defects that we see in patients who have glaucoma are inferior nasal steps that respect the horizontal meridian but not the vertical meridian and then eventually become an arcuate and insert into the blind spot and the blind spot represents the visual field, representation of the optic disc, and so arcuate and then eventually altitudinal field defects are the characteristic progression of peripheral field loss of glaucoma. But because the papillomacular bundle is relatively short and straight to the disc, it's usually preserved and that means acuity is normally preserved until very, very late in glaucoma. So, when we see non glaucoma disc cupping, the things we are trying to differentiate between glaucoma and not glaucoma are actually not related to the pressure, the interrogative pressure per se. The features that are going to suggest that it may be non-glaucoma disc cupping are if the cup does not equal the visual field effect. So, if you have a 0.5 cup but your field is only five degrees wide, that's a mismatch between the cupping and the field. We also don't want to see any kind of vertical visual field defect because the glaucoma field defects respect the horizontal, not the vertical. So, if we have any kind of homonymous character of the field respecting the vertical meridian, or bitemporal character to the field where it's respecting the temporal meridian, those things are not going to be glaucomas. And if we see pallor of the rim, so when we're looking at the doughnut, we should concentrate less on the hole and more on the doughnut. So, if we see the pallor in the rim, that means we should be worried about non glaucomatous optic atrophy. If the pallor matches the cupping, that's kind of glaucoma. So, the things that would prompt me to say "well this is cupped, but this is not glaucomatous cupping," are if the speed of the vision loss is too fast-glaucoma is a super slow disease-so if it's a super-fast visual loss, the tempo doesn't match glaucoma, if they've lost acuity or they have a central scotoma because they have papillomacular bundle, that normally does not occur until very late in glaucoma, if the field defect is temporal rather than nasal because it is normally the temporal fiber which is the nasal field, or if the field defect is respecting the vertical meridian rather than the horizontal meridian. All of these features are the features that are going to make me want to image someone who is referred to me as possible for glaucoma. So you should be aware that cupping is the ophthalmoscopic feature of glaucoma, but other things other than glaucoma can cup your nerves and if you have lost of acuity, it's too fast, you have rim pallor, you have vertical meridian, or you have a temporal visual field defect, you should be really thinking about imaging that patient. |
