Lecturer: Dr. Christopher Leung, The Chinese University of Hong Kong
DR LEUNG: May I ask Dr. Ting — what do you remember? Now, number one, I want you to remember is the diagnosis of glaucoma does not begin on the levels of intraocular pressure. Intraocular pressure — you mentioned the keywords — is not important in the diagnosis of glaucoma. And then a second thing I want to emphasize is the use of OCT for measurement of the retinal nerve fiber layer thickness is critical to make an accurate diagnosis of glaucoma. Very good. So we mentioned the retinal nerve fiber layer and we mentioned IOP. So I’ll finish off the lecture perhaps in another 25, 30 minutes, and then we’ll go for lunch. Again, just to remind you, this is the FDT, frequency doubling technology, visual field. And you see inferior nasal defects for this patient. By the way, glaucoma is the most common disease that will show a nasal — bilateral nasal field defects. But generally what you would expect to find here is the nasal defects — they often respect the horizontal midline. So glaucoma — you often see bilateral superior nasal defects or bilateral inferior nasal defects. So here is an example. You see nasal defects, and it’s bilateral. Now, remember this pair of optic discs I showed you on Monday. On Tuesday. All of you, almost, would think this pair of optic discs are glaucomatous. And I would like to use this example to demonstrate how deceiving it could be when you just study the optic disc size, optic cup size, and the cup/disc ratio. You can see the right side actually looks pretty cupped. And the left eye also looks cupped. And you can basically describe this optic disc as cupping. But the problem is… The evaluation of cupping is very subjective. The point is: How do you consider an optic disc as cupped? It’s difficult to judge. You do not measure it. But you just base it on your past experience. Seeing lots of normals and seeing glaucoma patients. And then you come to the conclusion… Wow, this disc looks a little bit abnormal. It’s unusual. And then you say… This is cupping. But the fact is there’s a huge variation in terms of the size of the cup, even in normal individuals. And likewise, there is variations in the cup size among patients with glaucoma. So if you just look at the disc, that would be very, very inaccurate. If you want to make a diagnosis of glaucoma. Now, how about the rim? I mentioned about the rim. It’s also one of the factors we consider to detect glaucoma. Now, again, when you look at the rim, you probably would mention it’s in the rule ISNT, inferior superior nasal temporal. It’s the reference that you are thought to evaluate whether there is rim narrowing. This is the reference. The inferior usually is the thickest, and then the superior, and then the nasal, and then the temporal rim. But, again, this is subjective. And it may not be very reliable. And how about the cup/disc ratio? In this slide, the cup/disc ratio, I would say, would be about 0.8, if you agree. So the cup/disc ratio of 0.8 is pretty big. Then you say this patient has glaucoma. Again, this is not accurate. The most advanced glaucomatous optic discs show a large cup/disc ratio. But there are also a lot of normal individuals which show a large cup/disc ratio. And there are also glaucoma patients with a small cup/disc ratio. So it becomes very confusing. And that’s why reading the retinal nerve fiber layer is more informative for you to judge whether this eye is normal or not normal. Now, although we see enlarged cup/disc ratio, perhaps narrowing of the rim over here, but we don’t see actually any loss of the retinal nerve fiber layer for both eyes. As I mentioned on Tuesday, when you look at the retinal nerve fiber layer, the red represents thick retinal nerve fiber layer. And retinal nerve fiber layer distribution is thickest over at the superotemporal and inferotemporal bundles. So this is what we call as the RNFL, retinal nerve fiber layer thickness map. And this is a very normal-looking retinal nerve fiber layer thickness map. So when you study the retinal nerve fiber layer thickness map, you can compare the distribution of the bundles over on the superior side and the inferior side. And then you also compare the right and the left. Basically check for symmetry. But the inferotemporal retinal nerve fiber layer generally is a little bit thicker than the superotemporal retinal nerve fiber layer bundles. So you see a little bit more red over here than here. Likewise, you see a little bit more red over here than here. Now… So based on the retinal nerve fiber layer profile, you can be sure that this patient does not have any optic nerve disease. Despite the fact that the cup/disc ratio is increased, despite the fact that the rim perhaps looks a little bit narrow. Now, let’s look back to this patient. So we have here again — when you study the retinal nerve fiber layer, you study the symmetry. What you can appreciate here is that there’s a symmetry in the distribution of the retinal nerve fiber layer between the superior side and the inferior side. So loss of the retinal nerve fiber layer over here… And loss of the retinal nerve fiber layer over here. For both the right and the left. And this corresponds to the visual field defects. But you have to be careful when you interpret the retinal nerve fiber layer thickness deviation map. As I mentioned the other day, you are familiar with this OCT’s profile, retinal nerve fiber layer profile, after circle scan. But again, I asked you to move away from these circle scan measurements to look at the map measurements. I always ignore this part of the information. So when you study the deviation map, what you can see here — there is a correspondence between the thickness map over here — you see thin retinal nerve fiber layer, and you also see red pixels. So red pixels mean the measurements here are below the normal reference ranges. And the question I have for you here is for this eye. For the left eye. The question I have for you is: Now, we are comfortable and we can say the right eye is abnormal, because this eye has superior retinal nerve fiber layer thinning. The question I have for you is: Is there any inferior retinal nerve fiber layer thinning? Now, we see the deviation map. This is showing red. Those of you who like to study the circle scan — you see the 6:00 is also red. So let’s have a show of hands. How many of you would think the inferior retinal nerve fiber layer is abnormal? Is thin? Anyone? Okay. We see one hand. Two hands. Three. Okay. How many of you would think the inferior side of the optic disc, of the retinal nerve fiber layer, is normal? Very good. So actually we have half-half. But when we have disagreement between the thickness map and the deviation map, we always would look at the thickness map as a reference. It’s very interesting for us to see the inferior 6:00 and also in the deviation map this part is abnormal. But we also need to understand the anatomy of the distribution of the retinal nerve fiber layer also varies between the individuals. I’ll show you another example. Here again is one of our research patients. Coming back for follow-up. And this is the optic disc for both the right and the left. Now, this is a very typical myopic optic disc. Is myopia coming here in Vietnam? So you do see these pictures a lot. You do see this type of optic disc very often. They are difficult to examine. Difficult. You agree. Because these optic discs are often tilted, and also they have very extensive areas of parapapillary atrophy. And you see this patient is -8 diopters. Sorry. This is right eye OD and this is left eye OS. It’s a high myope. When you only examine the optic disc, it could be, again, very confusing. Here you see an enlarged cup/disc ratio. It’s not as big as the previous case. But you see the cup/disc ratio in this case would be at least 0.7. When you follow the rim, it appears also that the rim here is pretty thin, over on the temporal side. And then you’re confused. Whether this eye has glaucoma. But I would like to, again, have a show of hands how many of you now think, with the pictures we have here, would think this patient has glaucoma? Nobody? How many of you would think this is actually a totally normal individual? Very good. So you all learned very well. Now, that’s why you see OCT plays a very important role, telling us whether an eye has an optic neuropathy. Now, listen carefully. What I mention here is not glaucoma. Whether this eye has an optic neuropathy. I will talk about that a little bit later. But now, looking at the deviation map, you see all these red pixels. And when you look at the circle scan, I’m sure when you study the circle scan in those three printouts, you will appreciate there is red sectors over on the inferior side and the superior side. In the map, we see more red. The question is: Are these regions abnormal? And the answer is: They’re not abnormal. They’re normal. And you can see very clearly the retinal nerve fiber layer is quite red inferotemporally and superotemporally, for both the right and the left. And the reason why we see abnormalities over the deviation map is because the normative database we use for determining whether a pixel is normal or abnormal is from individuals who are largely non-myopic. And as I said, there are individual variations in the distribution of the superotemporal and inferotemporal retinal nerve fiber layer bundles. In myopic eyes, this superotemporal… So you see here is a case — we can measure the retinal nerve fiber layer bundle angle, inferotemporal, superotemporal. The angle between this bundle — we can measure it. And you can see the more myopic you are, the narrower this retinal nerve fiber layer bundle angle is. So when you look at this case, it’s high myope, the retinal nerve fiber layer bundles converge towards the macula, leaving this area relatively abnormal, compared with the normative database that the instrument uses to judge whether these regions are normal or abnormal. So that’s why you have to be very careful, when you interpret OCT. First of all, don’t just look at the rim. Don’t just look at the circle scan. Because the circle scan assessment could be deceiving. And even with the map, it could be deceiving, if you’re not studying the thickness map. Now, this is a case I saw when I was in the previous Orbis program, in Mainland China. So that hospital — they didn’t have a Goldmann applanation tonometer. They didn’t have visual field. But they had an OCT. Spectral domain OCT. So the doctors there — they show me this patient and bring in the scan. Well, they said, it’s a glaucoma patient. And asked me how to manage this patient. Now, what you can see here — the right eye — normal or abnormal? Normal, right? Very good-looking retinal nerve fiber layer distribution. Left eye — normal or abnormal? Abnormal. Right? Basically, when you compare right and left, you can seed less red over the thickness map, and we compare the superior and inferior retinal nerve fiber layer bundle. You see loss of the color over the superior side. So there is superior thinning of the retinal nerve fiber layer. The inferior probably, if you’re comparing to the right, you can also guess there might be some early thinning, on the left inferior side. Easy, right? So there is also correspondence — some thinning over here. Some thinning over here. Some thinning over here. The deviation map. So OCT is very powerful to tell you whether there is an optic neuropathy or not. But this is the optic disc of the left eye of that patient. So what do you see? Is it a glaucomatous optic disc or not? No, it’s not. It doesn’t look glaucomatous, because the cup/disc ratio is normal. And the rim is relatively normal. But as I said, that may not be a very reliable indicator of glaucoma. The most important feature that you pick up from this photograph is the color of the rim. Which looks pale. So when you look at the right eye, I hope you can appreciate better the differences in terms of rim color. So we just learned from Dr. Ho’s lecture — rim color, pallor of the neuroretinal rim, is an indicator of non-glaucomatous optic neuropathies. So that’s why I mentioned to you that OCT is very powerful, to tell you whether an eye has an optic neuropathy or not. But you always need to examine the optic disc yourself, using slit lamp biomicroscopy. Because you can only read the color of the rim when you look at the patient. So neuroretinal rim pallor was found to be highly specific for non-glaucomatous optic neuropathy. And when we see retinal nerve fiber layer thinning, and there is a pale neuroretinal rim, we have a list of differential diagnoses. So we have different etiologies of optic neuropathies. Ischemic, inflammatory, compressive, infiltrative, traumatic, radiation, infectious, nutritional deficiency, toxic, hereditary. A whole different list of different categories of optic neuropathies. And each category has its individual causes, and you need to work up, to determine what is causing the optic neuropathy. So fortunately, it’s actually not difficult to diagnose non-glaucomatous optic neuropathy, and it’s not difficult to identify the etiologies of these non-glaucomatous optic neuropathies. I don’t have time to go through every individual optic neuropathy with you today. But this is pretty textbook stuff. You can always refer to the internet to check the clinical history and features with reference to each of these optic neuropathies. And one last thing that I would like to also share with you is about RAPD. RAPD stands for relative afferent pupillary defect. So which eye has got an RAPD in this slide? So this is the right eye and this is the left eye. Left eye. Very good. So you all are familiar with RAPD. So I just want to clarify the concept about when you would detect an RAPD. Do you see — would you see an RAPD in glaucoma patients? Okay. Yes or no? How many of you would say no? How many of you would say yes? Okay. So would you see RAPD in patients with non-glaucomatous optic neuropathy? Non-glaucomatous optic neuropathies? So we see the other part of you would say you would see RAPD in non-glaucomatous optic neuropathies. Some of you would think you would see an RAPD in glaucoma. The point is: You will see an RAPD in every kind of optic neuropathies, provided that… Provided that one eye is worse than the fellow eye. Relative afferent pupillary defect. You have to digest this term carefully. So relative means relative to what? It’s relative to the other eye. So I saw some clinical notes the other day. I saw RAPD on the right eye and RAPD on the left eye. And this is not possible. Because it’s relative. So we can only see RAPD on one eye. And afferent. What does the word afferent mean? It means sensory. So we’re talking about optic nerve. It’s the sensory component in the RAPD we’re talking about here. Pupillary defect. So we have a problem with the pupil. So this is RAPD. So this term means you have an optic nerve problem. It’s a sensory nerve. And it’s relative to the fellow eye. Now, the second question I would like to ask you is: Would you be able to see an RAPD in an eye with visual acuity of 6/6? So if you have both eyes having visual acuity of 6/6, 20/20, would you be able to detect an RAPD? So how many of you would say yes, you can still detect an RAPD in both eyes with a visual acuity of 20/20? Okay. A few. How many of you would say no, we cannot detect RAPD when both eyes’ visual acuity are normal? Okay. RAPD can still be detected in a patient with visual acuity 20/20 for both eyes. It’s relative in terms of the relative loss of retinal ganglion cells. So when you see an OCT picture like this, you will see there is a difference in the number of retinal ganglion cells between the right and the left. So you have more retinal ganglion cells on the right and less retinal ganglion cells on the left. And then basically you would be able to see an RAPD for the left side. For this eye, we just mentioned earlier the retinal ganglion cell numbers probably would be very similar between the left and the right. Because you see the retinal nerve fiber layer thickness is pretty much comparable between the right and the left. So even though this patient is a glaucoma patient, I don’t think we can detect an RAPD for this patient. Some of you may wonder, actually — the left eye got a little bit thicker retinal nerve fiber layer than the right. The average retinal nerve fiber layer thickness measure d from the circle scan — 76 on the left, 71 on the right. So if your eyes are sharp enough, you might be able to detect an RAPD for the right eye. So again, the retinal nerve fiber layer tells you a lot about whether you will see an RAPD. But if you don’t have an OCT with you… Then an RAPD is actually a very handy clinical technique that you can master to determine whether there is an optic neuropathy or not. So one last thing I would like to talk is: This optic disc. When you describe optic disc, when you write down in your clinical notes, obviously this optic disc looks very glaucomatous. Many of our residents in Hong Kong would say this optic disc is pale. But I would just want to remind you that this optic disc does look pale.
>> Does look pale?
DR LEUNG: Does look pale, because the rim tissue’s almost gone for this eye.
>> The rim?
DR LEUNG: The rim tissue is almost gone. Disappeared. So this is a very end stage glaucoma. And when we comment the color of the disc, basically we are commenting the color of the neuroretinal rim. We are not interested to comment on the color of the cup. Because the cup is pale anyway. So we described the disc as pink or pale. Pink is the term we use to describe normal-looking, normal color ophthalmic disc. We use pink. Pale means normal is actually easy. The disc is either pink or pale. I would encourage you to be more specific. Instead of saying the disc is pink or pale, you should say whether the rim is pink or pale. Because in glaucoma, what you can see here is the remaining rim tissue actually looks pink. It’s not pale. And pink tells me that this is not non-glaucomatous optic neuropathy. A pale rim tells me that this is non-glaucomatous optic neuropathies. So I will stop here, just to recap what we learned in the last few days. Number one, you don’t diagnose glaucoma based on intraocular pressure levels. Sorry. Number two, the diagnosis of glaucoma is predicated on a thin retinal nerve fiber layer and a narrow neuroretinal rim. And the reason why we also need a rim definition here is because all kinds of optic neuropathies would have a thin retinal nerve fiber layer. That’s why for diagnosis of glaucoma, not only you need a thin retinal nerve fiber layer, but also you need to examine the rim carefully. When the rim assessment is difficult, then the retinal nerve fiber layer can give you a more sensitive marker to tell whether the optic nerve is normal or abnormal. And the third thing I want you to remember is: When you see a thin retinal nerve fiber layer, don’t say it is glaucoma. As I mentioned, many times all kinds of optic neuropathies would have a thin retinal nerve fiber layer. And examining the color of the rim is important for you then to differentiate whether it’s glaucomatous or non-glaucomatous. Right. I think that’s all I want to tell you this morning. Thank you.