Lecture: Towards Constant Measurement of IOP

Outline of this lecture:

  • The impact of IOP fluctuations
  • Methods for assessing IOP fluctuations
  • Non-invasive devices

Lecture Location: on-board the Orbis Flying Eye Hospital in Bridgetown, Barbados
Lecturer: Dr. Malik Y. Kahook, University of Colorado School of Medicine, Aurora, CO, USA


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DR KAHOOK: This is a very big mountain that we haven’t climbed, as glaucoma caretakers. We hinted a little bit in a previous talk about someone coming in, getting a Goldmann applanation. It’s really a split second of intraocular pressure. The patient then goes home, different habitual positions. They might go exercise. They might sleep on one side versus the other. We really don’t know what’s happening to the intraocular pressure in those cases. So I’ll talk about the impact of IOP fluctuations. Why does it really matter to have 24-hour IOP. Methods of assessing IOP fluctuations, and then some of the non-invasive devices, and I’ll probably skip over a couple of slides to get to the meat of things, since we only have about 15 minutes to cover this. Now, intraocular pressure is the only modifiable risk factor that we have in glaucoma. I’m not telling you anything that you don’t know. But I think it’s worth thinking about this for a little bit, because even though all of our therapies are geared towards intraocular pressure, the amount of data that we act upon is very, very limited, and how can we increase that? How can we have as much information as possible, in order to make the therapeutic choices that we need to make? Now, how do we measure it? Typically by Goldmann applanation. We do it three to four times a year. It might be one to three seconds total time during that year. And 99.99% of the time, we have really no idea what’s happening. A single, static intraocular pressure doesn’t really tell us much about the true range of IOP, what the peak IOP is, what the variation is through the day, and 2/3 of glaucoma patients have their peak pressure, the maximum pressure — is sometime outside of office hours. So we don’t really know what that maximum is when we’re setting our targets for therapy. Short-term fluctuations happen often. When you’re looking at my talk here, and some of you might be falling asleep, because it’s almost lunchtime, and you’re closing your eyes. Each time you close your eyes, if you’re blinking and opening, that actually increases the pressure. Goes up with heartbeat. Intermediate. It can happen with medication effect. You put your drops in. There’s a peak and trough effect. So there’s always fluctuations that are happening. With activity, just walking up the stairs onto the plane or exercising during the day — that’s going to make your intraocular pressure fluctuate. Sorry, it looks like this is on a timer, so I’ll go back here. Long-term fluctuations include disease progression and treatment changes. If you’re doing a trabeculectomy, for example, that can make your pressure fluctuate over the long term. Circadian rhythms are present in healthy and glaucomatous patients. We know that there’s always a rise and decrease in your pressure throughout the day. The highest is usually in the early morning hours. It can slowly decline over time, and it might be due to different hormonal effects that are in the body. Aqueous humor production is different throughout the day. It’s going to be in the morning greater than the afternoon, which is greater than nighttime, and there’s a consistent elevation overnight, some of it due to the postural effect of just laying down on your back. So does fluctuation matter? It really depends. Of course, I’m not gonna go over all these studies, but different studies say different things. Is a fluctuation during the day something that matters? Fluctuation during a month, during a year? How does treatment effect actually factor into it? A lot of studies that looked at fluctuations didn’t really factor into it the fact that some patients were added on therapy, and that was the cause for that decrease, versus the initial increase in pressure. So the peak and trough effect isn’t always negated from observation of what fluctuations actually do to the eye, and that’s one of the limiting factors. AGIS — retrospective study over seven years. IOP fluctuation significantly associated with progression, with a subgroup analysis. The higher IOP group had no association. The low IOP group had a strong association. And you see here CIGTS and EMGT had a mixture of responses to what the fluctuation might actually contribute. EMGT — no relationship between fluctuation and progression. Malmo Ocular Hypertension Study, retrospective analysis. Three readings, and the IOP fluctuation in this case does not predict progression. Very big study. Very well planned and well executed study. Dr. Asrani out of Duke did a prospective analysis using home IOP monitoring. This is the iiCare tonometer that I’ll show you here in a little bit. And he showed that IOP fluctuation was a significant risk factor for progression. And that office IOP was a poor indicator of the fluctuations. And that’s, again, this snapshot of IOP that we get in the office — doesn’t really tell us that much. So there’s dynamic tonometry. There’s sleep studies that can be done. The diurnal tension curve, along with sleep studies and home monitoring — that can be done. Diurnal tension curves are something that we use frequently in our clinic, when we bring patients and check their intraocular pressure in the morning, sometime in the midday and then the afternoon. But you can also do it using a sleep lab, where you bring the patients in, you admit them, they come in from an 8:00 morning visit all the way through to the following morning, and get a full diurnal/nocturnal curve that I’ll talk about here in a little bit. The IOP readings, when you’re doing a DTC, are just one every one to three hours. Relatively easy and inexpensive, something you can do in your office, but it can be time-consuming for the staff in a very busy clinic, and you don’t have any data on the nighttime that you would ideally like to get, if you’re trying to get the entire continuum of what’s happening with the pressure. Now, in a sleep lab, the patients are admitted overnight. There are extra resources, extra expenses, as you can imagine, to get access to that. Some people who don’t have access to a sleep study lab will take patients into a hotel and check there overnight. Some offices can actually put a bed in one of the exam rooms and have that done. You have to be very motivated to do that. So in most cases, the sleep studies are not done unless you have access to a specific sleep lab. The disadvantages here: It requires admission. And in the US, it can be up to $900 overnight, so it’s cost-prohibitive, and it’s not covered by insurances, health care system, in our case. You can get the diurnal tension curve when you’re doing the tonometry in the office. You can get that covered. But when you add on the nocturnal, it’s actually not a covered service, so you can imagine how expensive it can get. Time-consuming. Still only static readings. You’re only getting the pressure when you’re checking for it. Poor representation of what’s actually happening with the patient, because in their home, they’re acting differently than they would when they’re in the sleep lab. They’re usually just sitting down or laying down in bed watching TV. They’re not doing all of the activities that they might do at home. I went over this slide already in a previous talk, just showing the previous therapies that we have. Some are significant. Some we know are insignificant, like timolol, and there’s a lot of room for research. So if any of you are looking for research topics to cover, looking more at the different effects over 24 hours of our medications would be something valuable to add to the literature. How close are we to 24-hour data? We have home tonometry. We have non-invasive IOP measurements that are being done. And we also have some IOP measurements that are being done. Home tonometry is getting a lot of attention, because now we have the iCare tonometer, that has wider access around the globe. Certainly in the US we didn’t have access to it before, but now we do. And there’s a version that the patient can take home. They can rent it from our clinic and take it home. The key here is it does not require anesthesia. You don’t have to give them proparacaine to put a drop on their eye. They can do this with the rebound tonometry. They don’t feel it. Very comfortable. And, again, there’s a home and office version of this, which makes it very handy. Sanjay Asrani did a lot of the early work on this, and he was able to show that it’s very accurate. That there is correlation with other methods that we use to measure intraocular pressure, and that patient versus technician — it’s acceptable. The performance of this device is acceptable across the continuum of where you want to use it, whether it’s in the office or it’s in the patient’s hands at home. The advantages is that you can assess daily variation. The IOP readings across multiple days. Because you’re giving it to the patient, they don’t have to come to the office. Readings from a normal activity standpoint — they’re taking their pressure during usually what their habitual activity is at home. So if they’re doing housework, they can stop and measure the pressure. If they’re at work in some capacity, they can measure their pressure. There’s no need for admission into a is sleep lab. There are disadvantages, of course, including cost, but you can actually rent these out to patients, so that several hundred patients are using the device. You just have to change the tips. This is no longer true that they’re not FDA approved, because now the home tonometry version is FDA approved, and we’re using it. Now, there are continuous devices that can be used. Many of these are now being studied, including implantables, where you can connect it with an intraocular lens. These are really not ready for prime time. We’re still trying to understand where they might fit in. But the continuous IOP therapy is where we’re headed. Something that is residing on the eye or in the eye, where it doesn’t require the patient to actively do something to measure the pressure. From a non-invasive standpoint, Triggerfish — this is a company called Sensimed — made a contact lens that measures the biomechanics of the eye around the limbus, which by their estimation correlates with intraocular pressure change. The contact lens goes on in clinic. The patient can go home. They can go about their business for 24 hours. They come back in the next day. The contact lens comes out, and the information is recorded on a recorder that can be clipped to your belt or worn around your neck. It’s very similar to a halter monitor that’s used for a blood pressure check. It’s a very similar concept. Continuous non-invasive ambulatory. The patients can go about their business. They can really do almost any activity with these on. The device itself is CE marked, and just recently became FDA approved, so you’re starting to see some places use this for research purposes. This is just what it looks like. That’s the recorder I was talking about. It can be worn around the neck. It can be worn on the belt. And again, it’s fairly non-obstructive to what you want to do. But you can tell that the patient’s wearing it. So this is what it looks like on the patient, and when you’re going about your daily activities, it will be very noticeable, that you have this on. If you look at the eye, you can see that it’s also a different color, because of the electrodes that are on the contact lens. We did a study just looking at the comfort, and we found that it was fairly well tolerated. That it doesn’t decenter that much, which was a worry that I had. If it’s looking at the biomechanics and it’s changing from position to position during the day, it might give you faulty information, but it was fairly stable. But because of that, it actually sucks onto the eye, and it’s fairly tight on the eye. So patients do feel it. But we had very few discontinuations during the study we did. There are of course limitations. There’s not a one to one relationship between pressure and the output that’s coming from the Triggerfish. They’re still doing a lot of work to correlate the two. The conversion is difficult. It’s non-linear. And patients must be able to tolerate the contact lens, which, like I said, is fairly straightforward. One thing I really love about this system is that patients have been keeping a diary when using this, so you can kind of follow what they’ve been doing and what that does to pressure. So in this case, the patient came in, had the lens fitting, went to sleep for a little bit, and you can see what’s happening to the pressure here during the spike. The patient was cooking. Had a really good time cooking. You can tell there was a lot of activity during that. Watched a football game, which apparently was a very boring football game. Nothing really happened there. And then you can see he woke up, and the lens was eventually removed. So here’s a case comparing right to left intraocular pressure. Just really to give you a sense as to what kind of graph you get, what kind of input. The initial IOP, the end IOP, and several fluctuations that can happen. A lot of times, when you’re seeing the fluctuations in pressure, it’s happening because of blinking or different activities that the patient is doing. But it’s not something where you can look at it and say: Well, this is intraocular pressure, and I understand it one to one. It’s a little bit of a different output. You can see even right and left eyes can differ from one another, as to the amount of fluctuations that are happening. They just look different, one eye to another. We don’t know what that really means at this point. And here’s an interesting patient that came in with a very good diary. This patient went home after the fitting, had an argument with her husband. You can see what happened during the argument. There’s a lot of arguing back and forth, and had a lot of pressure changes. In Colorado, marijuana is legal, so then she went outside and had marijuana, and you can see she got very mellow after that. It’s funny. When I said marijuana, everybody in the room started paying attention. So I’ll talk more about marijuana to gather your attention. And then went to sleep, went to the bathroom, got disconnected. And so we’re getting this type of information that we weren’t getting before. So I don’t know how popular Inspector Gadget is in Barbados, but this is one of my son’s favorite cartoon characters, that has all these gadgets coming out of the hat. We’re starting to get there in medicine, where we have all of these wearables. Some of you might have the Apple Watch on. FitBit. I see a lot of that from an exercise standpoint. We’re starting to gather all of this information. We really don’t know what to do with it quite yet. I have a lot of patients who come to me now, and they give me the output of their FitBit. How many steps they did. And it’s like… Well, I show them my steps, and I tell them… Okay, that’s great. We just compared the amount of steps that I did in clinic today. I don’t really know what to do with it, other than to say at some point I think we’re gonna have to understand how we use this information. So what does this mean for you? While it is the only modifiable risk factor for glaucoma, our assessment is not rigorous. I’ve said that a few times. Performing the diurnal tension curves and 24-hour IOP sleep studies might elucidate factors for progression that are not observed in routine clinic. Implantable devices are still years away from use. Something that I think we’re getting closer to. We’re just not there yet. Non-invasive devices provide useful information in some patients, and we’re starting to understand: The more we can use the Sensimed device, the Triggerfish, the more we’re gonna understand how to correlate the output with intraocular pressure. When disease is advancing despite apparent IOP control, similar to the previous talk that we had, when we’re not sure exactly what’s going on, consider varying the visit times of the patient. Coming in in the morning, versus coming in at night. If you look at your patients, a lot of them tend to come in only in the morning, only in the afternoon, depending on their work habits. But try and vary that. And then consider, if you have access to a 24-hour sleep lab, or you can do that in a different setting, that would be great. Otherwise, you can do these diurnal tension curves where you’re checking 8:00 in the morning, 10:00, noon, 2:00, 4:00 pm, and the patient goes home, and you’re getting a wealth of data. So think about IOP and think about how to get more information. Thank you.

May 25, 2018

Last Updated: October 31, 2022

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