OCT Beyond the basics with Hady Saheb, Ep 38

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[00:00:00] Show intro

Robert: In this episode, I go beyond the basics of optical coherence tomography, OCT, with Dr. Hady Saheb from McGill University. Our discussion includes ganglion cell layer analysis, structure function correlation, the floor effect, viewing software versus printouts, and explaining test results to patients. Visit TalkingAboutGlaucoma.

com for my social media links, provide feedback, leave a review, subscribe to my newsletter, and support the show, which remains advertiser free. I am now offering a value for value model. I'm Rob Schertzer, a Vancouver based glaucoma specialist, and we're Talking About Glaucoma.

[00:00:39] Welcome Hady Saheb

Robert: /Hadi Saheb from McGill University. Welcome to the show.

Hady: Thank you, Rob. This is great. I love the topic and love the opportunity to chat with you and and your listeners.

Robert: Ah, thanks. OCT. How, how could it get more exciting than that with all the advances in recent years?

Hady: I think so.

Robert: It's really changed the way I've [00:01:00] been practicing. And every time I attend another session about OCTs, it makes me rethink how I'm interpreting them. And it's also making me take so much time to get through going through the OCTs because I keep going, Oh, wait, , that's changed now.

 I better look at that again. So hopefully we'll touch on some of that. Part of the impetus for. Us getting together is each year. It's been what, four years now that you've co hosted this session at the Canadian Ophthalmological Society. I think

Hady: even more, it feels like forever.

I would say 6 or 6 or 7 is my best guess. Yeah. Okay.

Robert: I've been, I guess I've been to 4 of them and it's a, an OCT master class for glaucoma. Where you and colleagues go through lots of different cases, and what really struck me at the latest one was for a few of them that you present, you'd say, and here's a case [00:02:00] we presented before, and now we're thinking of it differently.

Hady: Yeah, I received, a few nice comments, but I'd say the strongest compliments were from people who said that the most impactful part of the presentation was when we both admitted to, some of them were real mistakes and some of them are just, different way to interpret things.

And I think that really resonated with people because. We've all been learning together. I wasn't around when phaco was being developed, but, when I speak to colleagues that were there as phaco was being developed, they were learning on the job. And it's similar with OCT.

We're continuing to learn. And you're talking about how It's taking you more time, and I totally agree with that. At first, it was just looking at the OCT and the initial diagnosis. And then, eventually, it was also looking at the progression analysis. And then we added on the macular OCT and the ganglion cell analysis and the progression for that.

And so now, all of a sudden, there's, a number of additional diagnostic testing to look at that is taking more time. But my [00:03:00] real opinion is it's, there's no question it's Providing better care and allowing us to detect progression earlier than we did, likely with just visual fields and looking at optic nerves.

So for me, it's a I agree that it takes more time, but for me, it's a huge win as well for patient care. So absolutely. I'm very focused and excited about OCT. It might be my favorite part of glaucoma follow up looking at OCT.

[00:03:27] Ganglion Cell Layer

Robert: /Awesome. So one of the things that. Really changed in recent years, I'd say, and you'd probably agree is the ganglion cell layer analysis that we do now.

How did we get there? In the past, we were always talking, at least during my training, glaucoma was about the optic nerve and, the nerve was getting more excavated. And then, if you get, more technical, it was the rim that was getting thinned. It wasn't that the nerve was getting more cut out, but now we've stepped back.

We've gone to the nerve fiber layer. And now we're back to the [00:04:00] ganglion cell layer.

Hady: Yeah, isn't that interesting? I think the way I try to describe it to the learners with me is that we're still looking at the nerve. We're just looking at in a different way, right? It's all 1. nerve axon cell, right?

And that cell starts in the ganglion cell layer and then it travels through the retinal nerve fiber layer and then lands in the optic nerve, which is the rim that you just described, and then goes through the nerve, the chiasm, the tract, and finally the LGN. So it's really all, whether we're looking at the nerve, The RNFL or the ganglion cell.

It's all the same. It's all the same tissue. It's just that the distribution is different and the way we're looking at it's different. The tissue, the layers we're segmenting are different, but it's all the same pathway. And I think that's one of the highlights is that, by looking at the same pathway in different areas

Some snapshots are giving you more information than others. So in some patient, the ganglion cell analysis is giving us more useful information than the RNFL, and vice versa. [00:05:00] They're truly complementary. And and studies have supported that, the the area under the curve, for example, for your diagnostic accuracy for glaucoma is Pretty similar for ganglion cells compared to our NFL.

So again, it's all, yes, it's a different part of the eye that we're looking at, but we're still looking at the nerve tissue just in a different way.

[00:05:19] Structure-Function Correlation

Robert: /And also in recent years, there's been the the functional correlation with this. So this is the anatomical damage that we're looking at with a ganglion cell.

And in recent years, we now have the use of the Humphrey 24 dash two C. Where this extra 10 points within the macula are being included with our visual field analysis because those points, which we always used to say, okay, glaucoma usually starts in the periphery, unless it's normal tension glaucoma, then it could be more centrally, but we're finding part of that is because we were doing the six degree steps throughout the The visual field [00:06:00] and missing early changes in the macula.

So it's all, it's great when we get this correlation between the OCT and now the 24 2C. I

Hady: agree. I agree. And definitely when I'm seeing ganglion cell defects I'm more likely to push or do more frequent central visual field tests, whether it's with a 10 2 or a 24C. So really agree with that.

[00:06:24] The "Floor Effect"

Robert: /When we get to the ganglion cell, I guess with the nerve fiber layer, Analysis as well. We talk about the floor effect. Do you want to comment on that for our listeners?

Hady: Yeah. And my first comment is I wish it didn't exist because my life would be so much easier for patient care if there was no floor.

So yeah, the floor effect is real. And so what is the floor? The floor is that we know that even, I like to use a dramatic example and I'm talking to learners, even in somebody who's unfortunately NLP, who's got a 1. 0 cup to this ratio, your RNFL is still [00:07:00] not zero, and so that depending on the machine you use, The aren't a felt floor somewhere between the forties and the fifties.

And that's based on, the structural tissue. It doesn't necessarily have to be live tissue, but just the remaining structure of the tissue, even after it's completely dead, unfortunately, there is still some thickness to that. So that's what we call the floor. You start with a completely healthy nerve and if you take it from a

Perfect nerve all the way down to 1. 0. You're going to come down and have that floor in the forties or fifties. So why is that relevant to our discussion? The closer you get to the floor, the less likely you are to detect structural progression. And so the general principle is In more advanced patients, you're less likely to detect structural progression.

So I like to talk, and this is really simplifying, Rob, but I like to talk about three phases of glaucoma progression. And the first phase is when you have structural progression and no functional progression. So it's just structural change in the beginning and your function remains normal. And then the middle.

[00:08:00] Correct. Correct. And then your middle phase, where you're likely having both structural and functional progression at the same time. And then your later stage is when you've reached your structural floor. But your function continues to progress. So why do I like to separate in those three categories?

Because I know What I'm focusing on most, although I'm looking at structure and function at all phases of disease progression, but earlier on when visual fields is to a normal, I'm making sure to spend the time, the necessary time on, on structural evaluation. And then when I've reached my floor structurally, then I'm spending even more time looking at the functional progression analysis.

So that's I like to separate into those three categories. And I think the other point when we're talking about the floor and since you opened the topic on ganglion cells is that there's a floor for both RNFL and ganglion cell. But there have been a few useful studies that have suggested that the floor for ganglion cells occurs later.

So there's one one interesting study that looked at whether [00:09:00] RNFL or ganglion cell progression predicted. Visual field progression and it showed that in the more advanced patients ganglion cell progression was was more able to predict visual field progression. So suggesting that the floor effect and ganglion cell likely occurs at a later stage than rnfl.

In summary, I look at rnfl ganglion cells visual field at every stage of the disease for all patients. But I know that earlier on, I'm looking more at my structure. Later on, I'm looking more in my visual field and also of the structural evaluations, RNFL or ganglion cells. I am focusing more on the ganglion cells as we become more advanced.

Robert: Yeah, I had a couple of examples today of that rnfl floor effect where I had to align the ganglion cell layer. And I've come up with, I wrote it down. This is a new canned phrase I created for my OCT reports saying rnfl trend all over the place, gcl trend stable. The rnfl analysis looking at each quadrant, [00:10:00] temporal was like this, inferior was like that superior was that. The curves were just everywhere. And you look at the numbers, they're just completely different each time. But then you look at the GCL and five visits, just nothing's changed on the GCL, so that's been very helpful, but a comment though, with.

[00:10:19] VF flattening FOS curve

Robert: /Relying when you have advanced damage and you have to rely more on the visual field, that gets me a problem too, because with the visual field. The frequency of seeing curve flattens out more as the mean deviation increases. So you start getting much less reliability with the visual field. So how do you overcome that if now you're relying mostly on a visual field?

Is there another visual field strategy that you do to? Try to look at that function.

Hady: It's the struggle of following advanced glaucoma patients. It's for sure a struggle. I think I'll, I'm more likely to do more frequent [00:11:00] testing. And I think as we get more advanced, 10-2s can often become more, more useful.

And I find it more helpful in allowing me to detect progression and Also, in the context of, normal pressures, I'm a little bit more forgiving for visual fields variability, and also I look at, the history of the patient and the patient's been variable all along. And I'm going to be a little bit more forgiving variability if they've been Really stable along and I'm going to worry a little bit more about the visual field looking different today.

So I think we've all learned in glaucoma, one abnormal visual field in the context of everything else being stable. You don't necessarily make a big management decision based on that. I tend to call that isolated visual field defect. When everything else is stable, but if you have a pressure of 19, and a visual field that's different I'm more likely to escalate treatment that visits and not wait for the next, but if you've got a great pressure, 12 no disc hemorrhage, the nerve looks similar to what it's looked like in the past.

I'll call that an isolated visual field change [00:12:00] and, have the patient come back sooner and repeat testing and again, a visual field that's looking at the overall trends. It's hard to make big decisions based on one alone because of what you've mentioned, the variability.

Robert: There is another factor you could take into account as well, and that's when, the visual field, it's quite constricted, and you're relying just on 10-2, and not sure if it's worse, and that's when the patient says, my visual field's worse. So sometimes they're telling you that they've noticed things getting worse, so that's sometimes comes into play in management, at least for me, for my patients.

Yes.

[00:12:40] Viewing software

Robert: /Another thing I have on my list here viewing software. I definitely rely on the software when in the room with the patient when I'm reviewing the OCTs. I don't know if some people are still doing printouts. Do you have a comment on that? Are you a software person and [00:13:00] big advocate for it?

Hady: For sure, a software person.

My clinical practice is mainly in, in two different sites. And in one of them, I've had access to for for 6 or 7 years. And at the other site had got access to it just 2 years ago. And. So I feel pretty comfortable, sharing my feelings about the contrast between the two setups and in that gap of four years where I had Forum at one side and not at the other.

It really felt different. I had so much more confidence looking at my progression analysis using the forum software. so what I do is when I'm using forum is There's a button called structure function. And so I press on that and it really gives you visual field RNFL ganglion cells and progression for each both event based and trend based.

And then if you have any disc photos, it's all there on one page. So for progression, also software can imagine something more useful. And I think the caveat, [00:14:00] though, is for initial visits. Because for, the way I look at the way I look at the progression analysis, as I mentioned to you with the structure function tab is you really do one eye at a time.

And I like on first visits to look at both eyes compared to one another because it helps me in my diagnosis. Is this glaucoma or not? Am I just leaving a suspect? Am I starting treatment? How asymmetric are the eyes? So looking at both eyes and I'm beside the other, I find that really useful instead of flipping from right eye page to left eye page.

So again for the first visits if the diagnosis is ambiguous, I really like comparing the right eye to the left eye one printout both for the RNFL and the ganglion cells. But once I've done two or three and I'm starting to focus more on stability of disease, then I really think that the viewing software looking at one eye at a time is where I get the most of my bang for the buck

And that's what I focus on.

Robert: And that helps too. If you're deciding, Oh, I better look at the GCL progression instead of the RNFL [00:15:00] progression. You have it all right

Hady: there. It's exactly. It's all there. Exactly. How about you? What do you do?

Robert: Completely software viewer. I have a different OCT. I'm using the TopCon Maestro 2.

So again, very easy interface.

[00:15:17] When do you review the OCT

Robert: /And the related to that, when do you look at your. patient's OCTs. Is it when you're seeing the patient or do you spend some time the day before or the morning of to take to be able to, because like I said, it's now taking longer and longer to go through these OCTs. How do you fit it in?

What's your workflow?

Hady: Yeah, I've heard different versions of this for myself. It's always when I'm seeing the patient, that's been my preference. I I like to look at the whole picture all at once and why is that number one I want to think about it once just from an efficiency standpoint, I want to look at it and think about it and make decisions about it once I was like that when I took exams and I speak to [00:16:00] our learners, I said, I was the learner who, maybe had one question I went back to, whereas I think many others will label 10 or 15 multiple choice questions they go back to.

 I went through them once, I didn't think I was going to become smarter, an hour, two hours later. And so I said, this is my best guess about this. And it's similar for my clinical values. So I want to look at it once. And so I do it all when the patient's there.

So I'm speaking to the patient to see how they feel. I'm measuring the pressure. I'm looking at the disc and I'm looking at the functional and structural diagnostic testing all at once. It takes a little bit more time. Sometimes it can be distracting because if patients see you, they're keen to share with you certain things.

And you have to be comfortable kind of navigating that multitasking. And often I'll, if it's nothing too urgent, I'll just ask the patient to give me some time to look at the testing. And then we get the chance to chat, but yeah, so for my workflow, it's after saying hi and how are you to the patient?

It's the first thing I do. Okay. Because ultimately the glaucoma disease state is based on your structure and function. The other things we look at are risk factors, whether it's the pressure, the presence of a disc [00:17:00] hemorrhage, those are risk factors, whereas the disease state is that. So I like to start with that.

And then I move on to looking at the chart, seeing what the pressure is, the vision examining the patient and then making a global decision.

Robert: Yeah, good point. Yeah I do that too. I had tried at times reviewing the OCTs and fields the night before, but it's like you said, it's a matter of efficiency.

I wasted all that time and I'm going to have to reopen those tests again when I'm with the patient anyway. So there's a lot of time wasted.

Hady: Yeah. And an example where that would become, unproductive in my mind, let's say, we all have patients with artifacts or some segmentation error or a visual isolate what I just called an isolated visual field change.

And so if I have an isolated visual field change. But my pressure is perfectly normal. There's no disc hemorrhage. I'm going to call that an isolated visual field change. But if I have an isolated visual field change, but I haven't examined the patient yet, haven't measured the pressure, then I have to label it as a change.

And then I have to [00:18:00] see the patient. If the pressure is high, then I'm going to do something about the visual field change. If the pressure is normal, I'm going to label it an isolated visual field change. So all this thought process that happens so organically and automatically when I'm doing everything at once is suddenly breaking down.

And and at least for the way I think in a way of function I think it would be quite challenging and

Robert: distracting. And then when the patient's there too, you realize there are these other things you hadn't noticed when you're just looking at the tests Oh, they also had a vein occlusion or a diabetic or they have macular degeneration, all of which mess up our tests.

And you really only notice it when you're putting it all together with the patient there. I agree./

[00:18:39] Explaining test results to patients

Robert: I also I have two monitors set up. It's not two one with the EMR and one with the test results. It's. One gigantic screen for me and one gigantic screen for my patients. So when I, the patient one is covered with a cloth and then I do the big reveal to show them their OCT and their field and I explain it to them.

So I go through a [00:19:00] lot of explaining each day. Do you try to explain it to your patients as well?

Hady: I love that idea of having the the sheet over it and then you show it to them almost like a surprise. My screens are open, very much visible to the patients. I tend to go with the flow of the patient.

Some patients will, show some curiosity and then I'll give, give them a little bit more information. But others are I feel at least looking for my global opinion, is. Is my situation stable? Do I need to do anything about it? And and so in those patients, they have access, they see what I'm looking at but I'm not necessarily diving deep into the details.

I do have a routine of whenever there's a photo, I tend to open it anyway. And I mentioned that it's a photo. I find that's a little bit more visual. People have looked online where I've seen that before, and it's nice for them to see the nerve. I know I would be excited about seeing my own nerve.

So nerve photos, I tend to, Deliberately describe it for the testing. I go with the flow of the patient and share comments based on their level of interest. [00:20:00]

Robert: Fair enough.

/

[00:20:05] Marker

 did you have any other things you wanted to bring up before I asked you the bonus question?

Hady: I think when we're talking about workflow some of us practiced virtual, tele glaucoma prior to the pandemic. I started during the pandemic. And in terms of my workflow, of course, for patients seeing me in person, those patients are getting, all their testing on the same day, unless there's a particular challenge with with patient volumes on that day and for those who are during virtual visits, they're coming on a quieter day to do their testing and and then I'm evaluating the test in an asynchronous fashion. And and speak to, but even those patients again, I'm evaluating their testing while speaking to them while hearing from them, how they're doing while looking at their clinical information, whether it's their visual acuity, their medication compliance, their pressure.

So it's a similar concept for me, whether I'm evaluating them in person or or virtually the differences [00:21:00] virtually, of course, the testing is done on a different day. And I'm not physically seeing them in person. How about you? Are you practicing a significant amount of of teleglaucoma or are you doing mostly in person?

Robert: I did, when COVID had hit and much as it sounds you were doing, the patients would come into the office And get the test. Basically, I was doing the tests on a different day and then I would just call them out, call them with the telehealth call to discuss the test results. Then I will be able to share the screen through zoom and do what I would do in the office.

It was actually because of what I was doing during COVID over zoom that I installed the second monitor. Because that's when I saw that more patients than I thought really were interested in seeing the results and I've been doing that ever since with the patients in person. Yeah,

Hady: that's that's great to know.

I'll I'll maybe try that out a little bit more often than I do now. Thanks for sharing.

[00:21:58] Expect to have glaucoma patients

Robert: /So now the [00:22:00] bonus question, it has to do with, with setting up an office, if you had advice for someone starting their practice, what did you wish you had done that you didn't do when you first set up an office?

That you would give advice to a young person setting up their practice?

Hady: That's a great question. I will start by saying I'm not sure I'm the best person to answer that question for a few reasons. The majority of my practice is at our academic center. Whereas you can imagine I'm not the person making those decisions.

 in terms of your specific question. I'm probably not the ideal person because I was never in that situation. I think you know what I understand from it. Even non glaucoma specialist is that glaucoma in every practice, even if you're, even if you're not focused or catering to glaucoma patients, there will be glaucoma patients in your practice.

So I think setting your practice up for glaucoma care is just so critical. So you need to have all the things we've talked about, whether so [00:23:00] visual fields and you can choose the one that you're, you feel comfortable with Some kind of structural structural testing an ability to take photos.

I think corneal hysteresis is becoming, more and more convincing that it does play a role in our diagnostic ability for glaucoma and our risk stratification. I think anterior segment OCT. I give a course about that and at the academy, so I'm a little bit biased towards its importance.

I have to say that in, run of the mill routine glaucoma practices, I think a good gonio is pretty good, frankly. And you still, we're still not at the stage where we can skip the gonio. I think the, even in a perfect entry segment OCT, you still need to use the gonio to look for certain parts of the angle.

And so I think anterior segment OCT is useful. I think if you're limited in terms of your options, maybe that would be one to skip. Although with almost all your post your second OCTs now you can do an add on anterior segment module, which is, pretty space efficient and cost efficient.

So it's probably worth [00:24:00] considering that. And then and then think about how you want to manage this patient. So I think if you've got a significant significant capacity in your staff. It's always easier for patients to do all the testing on the same day, but I think for leaner teams, it just makes sense to have the testing done on a different day.

And then on the day where the physician's there, you're a little bit more focused on, bringing the patients in, having them see the physician and and move on. So testing can be done asynchronously there. The other. Part I wanted to share is

[00:24:28] The work culture

Hady: /the work culture with your team, so how are patients requests answered, and for example, in some environments patients are always encouraged to go see optometry care for any new complaints, and sometimes it's very appropriate.

But in glaucoma practices, where a lot of the complaints are related to the drops, for example, I really want to manage those problems myself, because I can think of an example. Somebody had an allergy, was sent to an optometrist, was given steroids, because the allergy wasn't recognized, the pressure went up, then they spiked and they ran into other [00:25:00] troubles, whereas I think managed by an ophthalmologist or a glaucoma specialist who would recognize that right away, stop the drops, move on to something else, and it would be a much more simple simple process.

So I think. Those kinds of, the work culture, how you manage patients. I have found that to be a recurrent discussion point in some practices. And I think it's worth, for anybody new, starting to ask those questions early on to make sure you're in the right place, you're, you, there's a right fit between you and the practice you're working on.

[00:25:27] Patient questions

Robert: /How do you allow your patients to reach you? Are they, is there a phone line that they're using? Is. Do you have a patient portal in an EMR or.

Hady: Yeah, so the, because I work in larger practices right where they have their, separate and their entry points for the practice whether it's academic practice or the community practice.

There's a phone line to reach for both those practices and an email as well. But in busy practices, those phone calls are not [00:26:00] always answered and in the time that we would hope for, right? So patients sometimes are waiting and we try to have those disclaimers that if something's urgent to, present in person, whether it's at the office or an emergency room, but that still leaves the patients with some anxiety while waiting.

And in an ideal world, there would be a way to, get an answer same day for some of your concerns. And that's what we're working on. Yeah,

Robert: I think we're same here, still trying to work out the best ways to do it. An EMR portal is good, but when the average age of your patient is 80, they're not always as computer savvy.

Yeah. And the phone lines just don't stop. So it's hard to, it's hard to get through. Correct. Lots of staff.

Hady: And we're still, I don't know how it is where you are in Vancouver, we're definitely in catch up mode. And it really feels, like post pandemic catch up mode is, it feels like it's at least another year, because just so many months of a few months of complete shutdown and then [00:27:00] so many months of slow down.

And in fact, we're not up to 100 percent still, so you can just imagine that it really feels we're in this, we're in this in this wheel and it just keeps going. So I'm hopeful that in a year from now, we'll finally reach another steady state, but we're still in catch up mode where appointment delays are still beyond what we'd hoped for.

Robert: Thanks so much. This has been a great conversation. I hope our listeners are getting a lot out of this once this gets posted. Great.

Hady: Thank you, Rob, for the great questions and the opportunity to share some thoughts and learn from you as well. And I wish a great great day to all your listeners.

Thanks.

Robert: Take care.

/

[00:27:44] Outro

Robert: Talking about glaucoma is a podcast of indeterminant, frequency and duration though I am striving to get back to monthly with your support. Please rate the podcast on your pod player of choice, subscribe to it and tell your friends about it. Visit [00:28:00] TalkingAboutGlaucoma.com to find all my social feeds, subscribe to the newsletter, provide feedback and register as a guest if you want to be on a future episode. Keep informed to prevent needless loss of vision from glaucoma. See you next time on...talking about glaucoma