| Transcript |
All right, today we're going to be talking about optic disc drusen. These drusen are different than the retinal drusen that we see in age-related macular degeneration, which has nothing to do with these drusen. They both have the same word however, and it means like a rock or crystal in German, druse. And so, these rocks of calcium and other debris-axoplasmic debris-can appear inside your optic nerve, and when they do that, it can cause an optic neuropathy. So, here your optic nerve is, and it has the rocks in it, and sometimes those rocks are visible because they're on the surface. And so, usually, the visible optic disc drusen are no problem to make the diagnosis and you don't need to do any tests on the person. Some people believe that we should treat the intraocular pressure if it's elevated or they're ocular hypertensive because it's going to be hard to tell glaucomatous-type cupping in this and the field defect of disc drusen and glaucoma look very similar. So, the field defects in optic disc head drusen and in glaucoma tend to respect the horizontal meridian. The inferior nasal step is a super common type of visual field defect, but it can be arcuate in shape or it can be nerve fiber layer of any kind of distribution. What it doesn't usually do, is it usually spares the center. So, the papillomacular bundle usually is spared in patients with disc drusen just like glaucoma. And, when you have disc drusen that are visible, it's not a problem-it's when it's invisible to you because it's underneath. So, the buried disc drusen are the ones that look like papilledema. And so, we're going to be looking for the distinctive and obligatory signs of papilledema in any patient who has an elevated disc, and if we see the obligatory signs, then we're not going to be thinking about drusen. So, the obligatory signs in papilledema are when you have obscuration of the nerve fiber layer, and that's on the surface rather than deep. So, if we can see through the nerve fiber layer and see the vessels clearly, and if there's pigmentary change under the vessels, then that's going to be pseudo papilledema. But if we see the obscuration is in the nerve fiber layer and obscuring the blood vessel, that's going to be more suggestive that it's true disc edema. The other things that are obligatory signs that you're dealing with true papilledema are pathologic signs like hemorrhage, exudate, subretinal fluid. If we see those obligatory signs, then we're going to be leaning towards true papilledema or other causes of disc edema, and away from disc drusen. Now, what if you don't have any obligatory signs and you're still worried it's papilledema? Well then, you have to do ancillary testing, and the testing that we normally are going to rely upon is ultrasound. And, ultrasound is going to be looking for the calcifications that are in the drusen themselves, but it's only helpful if it's positive. So, if it's negative, about half the drusen are not calcified and we cannot see them on ultrasound. We also pair that with a 30-degree test where we're looking at the fluid in the sheath. And by moving the eye 30 degrees into eccentric fixation, the fluid kind of pushes out of the nerve, and so we can tell if there's fluid in the sheath. And, there are a number of ultrasound criteria for determining fluid in the sheath. And, you can use OCT. And, on OCT, we can see the elevation uh- in the disc head itself. Usually, it's hyporeflective with a hyperreflective rim around it. And, we're going to be looking for the obligatory signs. Again, the subretinal fluid, if we see that, uh- we probably shouldn't be making diagnosis with drusen. OCT is getting better and better, uh- but it's not a hundred percent sensitive or specific. Neith- none of these tests are. And, fluorescein angiogram-fundus fluorescein angiogram-probably is the best test because when we have true disc edema, there's going to be hyperfluorescence from leakage of the disc and that leakage represents the breakdown of the blood-brain barrier. And so, there are plenty of papers that are comparing these three modalities-fluorescein against OCT and ultrasound. In our clinic, ultrasound uh- works best if we see the calcification or we see the fluid in the sheath, that's probably good enough. OCT is kind of an adjunctive one. It helps establish the thickening and a baseline in a quantitative matter. And, we're going to be looking for that hyporeflective uh- drusen with a hyperreflective rim. And then if we're still unsure, we're going to do fluorescein angiogram to make sure there's no leakage. So, you need to know a little bit about disc drusen: it causes peripheral field loss, not central loss, it's slowly progressive, it's benign, it doesn't need imaging. If you see obligatory signs of papilledema, then you should work that up. If you're unsure, you should work it up as papilledema. Ultrasound, OCT, and fundus fluorescein are all adjunctive tests that help us differentiate these different uh- conditions from true papilledema. |
