Lecture: Rigid Gas Permeable Lens Assessment and Fitting: It’s Not That Hard

Rigid Gas Permeable (RGP) lenses can be used for any patient but can provide crisper vision for patients with high prescriptions and irregular corneas, with fewer health complications, easier lens handling and less frequent replacement. During this live webinar, we discuss some some simple RGP designs, how to insert and remove an RGP lens, the fitting characteristics of RGP lenses and how to assess an RGP lens on the eye.

Lecturer: Jason Chin, OD, FAAO, New England College of Optometry, Boston, USA


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DR CHIN: My name is Dr. Jason Chin, and I will be presenting a talk on rigid gas permeable lenses, assessment and fitting, and basically it’s not that hard. All right, so a little bit of introduction about myself. I am an adjunct faculty professor at the New England College of Optometry. A lot of you who have been on these webinars know that Orbis does work with us. I work in two private practices in Massachusetts, in the United States, and my general optometry interest is in specialty lenses, in particular keratoconus, postsurgical, orthoK, multifocal. Anything that has to do with contact lenses, I pretty much enjoy doing it, and I have a specialty in it. So just a little of an introduction of what I’m trying to do for today. So my goals are to have a brief overview of why we should consider rigid gas permeable lenses. I’m going to be referring to them in this talk as GP lenses, and as you notice, I’m gonna put them in parentheses as rigid. I had a question about why we call them rigid lenses. Are they moldable, and if not moldable, why rigid? At least here in the United States, among my colleagues, we’ve definitely had a little bit of discussion, and I think there is a certain argument that the nomenclature of rigid has stuck so much that, at least even in our patient populations, they refer to these lenses as hard lenses. I don’t think there’s actually a good term or a reason for why we call them rigid. In essence, you ever got these lenses. They are hard. As I’ll mention, one of the benefits of them is because they’re hard, they hold their shape a little bit more. They can be changed a little bit, but technically once they’re made, they are gonna hold their shape basically, too. So like I said, I don’t have a really good answer why it’s rigid, but we’ll refer to them as gas permeable lenses or GP lenses for the rest of the talk. I do want to talk about how to select and fit corneal lenses, in particular smaller diameter lenses. I did have some questions about scleral lenses, irregular cornea, stuff like that too. I will try to address that a little bit in the talk, but most of this talk is based on the key philosophies of fitting GP lenses. The evaluation of it, which can still be applied to irregular corneas, it just may not be as simple as a symmetrical cornea. But all the stuff that applies for what I’m talking about today can be applied to other lenses. I’m gonna review what properly fit GP lenses should look like, I have some slides of the fluorescein patterns, and I’m gonna review how to troubleshoot problems with the GP lenses. So my first poll question with the audience is: how familiar are you with the fitting process of GP lenses? One, I’ve never fit a GP lens, two, I’m familiar with the process in theory, but have never fit one on a patient. Three, I fit them, but not often enough to feel comfortable with them, and four, I fit often enough to feel comfortable fitting them. All right. So it looks like the majority of you have fit them, but not quite comfortable enough, with the rest of you guys fitting them fairly often. All right. The next question is: For those of you who fit them, how often do you fit GP lenses? Never, on occasions, once a month, or several times a month? All right. Looks like the majority have never fit GP lenses, or on occasion. Hopefully this will serve as a review to reset our knowledge and put things into a new or different perspective. All right. So why a GP lens? One of the reasons I’m talking about GP lenses in this audience is they’re relatively easy to obtain globally. In interactions with some of my international colleagues, I’ve never heard anyone who said they couldn’t obtain a GP lens. Soft lenses may be limited, but GP lenses are available. They are customizable. There pretty much isn’t anything I can think of offhand that I would not consider a GP lens for. They do provide a better quality of vision. They may be more cost effective than soft lenses, and they may be healthier than soft lenses. So poll question number three. Which conditions do you use corneal GP lenses for, and basically anything that applies to. So whether it’s normal cornea, high refractive error either in sphere or cylinder, postsurgical corneas, keratoconus, ectatic, degenerative, irregular corneal disease, or corneal reshaping/orthoK. All right. So it looks like a majority of you are using the GP lenses mostly for the irregular corneas, basically. None for postsurgical. And then the rest are for high refractive error. Okay, and I would probably say that the demographics here in the United States would be very similar for the population out there. Hopefully one of the things that this talk will change your perspective is that: Yes, we may reach for the more difficult cases in irregular corneas. There isn’t any reason why we can’t use it for anything else, basically. All right, so what are the benefits of GP lenses? So now we’re gonna go over the indications and some of the usage. In my opinion, cornea with high toricity is definitely a good usage. Corneas with irregular surface, postgraft and postsurgical corneas, aphakia, multifocal, and orthokeratology. Basically, as I said, I feel they can be used for any indication. At one point in the United States, they were used for almost everything. Then came the soft lenses, and GP lenses fell to the wayside. But I don’t feel like there’s any reason why practitioners can’t embrace the use of GP lenses. So I’m gonna be approaching it from the normal corneal aspect, basically, to the multifocal and orthokeratology — I’m not gonna be really talking about. But hard lenses can definitely be used for those applications, and orthokeratology definitely has to use a GP lens, and multifocal — even though we use soft lenses, it’s still more beneficial with multifocal lens. Benefits of GP lens. They have health benefits. They’re definitely more oxygen permeable, compared to some of the soft lenses. Depending on your area of the world, you may have a silicone hydrogel high oxygen soft lens available, but for those who don’t have the silicone hydrogels available, compared to the regular plastic polymers that soft lenses have, GP lenses will still have higher permeability. They have more deposit resistance, so the surface will be cleaner for a longer time, and because of the fact that the polymer for the hard lenses does not require actual fluid, it doesn’t necessarily dry the eyes up, or take from the natural tears of the eyes to maintain its wettability. The prescription is going to remain more consistent. With the soft lens, it can change its shape? If it dries up a little bit, that can change the optics. Hard lenses do not change optics. It’s more customizable, and you can get a more precise prescription, compared to toric soft lenses, where you have limited parameters. And the optics are influenced by the shape of the lens, which can be influenced by the shape of the eye. If you have a highly toric eye, the soft lens will change its shape. The hard lens will not. And also thinking about GP lenses, they are more durable because of the harder surface, and they last a little bit longer. Pricewise, they may last a year or two, if kept under good conditions. So before we start the fit, we have to ask ourself: Is the patient appropriate for a GP lens? I will say most everybody will be appropriate. There may be a few people for which they will not be appropriate, but for the most part, most patients will be. So if they are, we need to design and fit a lens. So first thing is, in terms of designing, comparing the empirical fit versus a diagnostic fit, basically. So poll question number four is: Do you fit GP lenses empirically or diagnostically? One no, I am unfamiliar with what that is, two, no, I only fit diagnostically, three, yes, I always fit empirically, and four yes, it depends on the situation. All right. So most of you have said yes. It depends on the situation. And a majority of you don’t even know what empirically fitting means. Okay, that’s what I expected there. So what exactly is empirically fitting a lens? For most of you who fit GP lens — and we put a lens on the patient, look at the fluorescein pattern, modify it — that’s diagnostic. We’re familiar with that. Empirically is before we even put the lens on the eyes, we get our measurements that we would have used to design it, and we call that into our lab and the lab actually takes that information using their nomograms and their databases and all the lenses they’ve designed in the past and they actually initially create that first initial lens. So diagnostically, unless you have a very large fitting set, diagnostically, the lens you put on probably may necessarily be close to the patient. Versus when it’s empirically, you’re expecting that hopefully it’s gonna be a lot closer to what it is. So one of the questions I had in the registration was: Is there any way to reduce chair time, both in irregular cases and those in just normal cases? So one of the pros about empirical fitting is that it can make the process a little bit more efficient. When it comes to irregular corneas, that a lot of you guys may be fitting GP lenses with, empirically may not be the best thing. In fact, the labs here actually discourage empirically fitting those types of lenses. However, with technology changing, that may actually change our philosophy and our approach may change a lot more, as time comes. With the technology change in corneal topography, there are some companies that are basically saying that empirically, with that information we normally provide, plus the corneal topography, they may be able to provide a better fitting lens than we might find in a diagnostic setting. So when it comes to empirical, the pros are: It is quicker and more efficient, basically. Now, efficient is all a relative term as well too. If we are talking about efficient for the patient, I don’t want to have a patient come in multiple times, basically. Diagnostic might be more efficient that way. However, if we talk about efficient — in our general practice, where in a very busy practice you may be allowed only 15 minutes per patient, and the longer you spend with one patient, the farther back you get your schedule. Empirically fitting might be more efficient, because you can at least in that initial visit — if you’re seeing them for a routine exam as well, get the information that you need and order the lens. So the next time you see them, again, to a certain degree, you can think of the clock as resetting again with another appointment slot. You have the lens and you can put it in that way too. Adaptation time, the vision time, may not take as long. Because empirically, it does take some of the guesswork out of it. These labs have nomograms and have a way to use other patients’ experience and other patients’ data to better fit your patient. They may provide a better first impression when putting that lens in. The edges may be a little bit different, because the base curve is gonna be more appropriate, because the prescription may be closer on and more accurate, your patient may have a better initial fit. Oh, wow, these lenses are great. The cons of them? In my point of view, there aren’t any cons to empirically fitting a lens. Going over to a diagnostic lens, there are definitely pros to that. You can see the fluorescein patterns almost immediately, so you can take that into consideration, to say… Oh, I didn’t think there was an irregularity there. But there was. I might need to change that lens a little more. You can determine if any subtle changes are needed to be accounted for in that aspect. When you do put the lenses on, you have that patient’s attention right there. Maybe your first time with the patient, you put that diagnostic lens on, and then you put the phoropter to overrefract them, you could give that impression of: Oh, wow, this is what my vision could possibly be with GP lenses but the cons are: It does take more official chair time. When you put the lens on, you have to wait for it to adapt. In the waiting room, it’s still your time at the beginning that you need to do. If you have a technician put it on, it may be more efficient, but it just depends on the flow of your office. Patients may get a false impression about lenses from the initial fit. As I mentioned, in terms of putting a lens on and putting the phoropter in front of it and saying this is what you can see, if those curves aren’t as precise, they may say: I feel the lenses a little bit more. I don’t know if I’m gonna be able to stand this lens. And for the most part, it requires a fitting set. In the olden days, when we did primarily hard lenses, we used to have large fitting sets. The size of what the fitting sets might be for soft contact lenses. Now most of the practices I go with have a standard… Basically have a base curve but no variation of power. As you know, for those who fit irregular corneas, if you’re fitting a more proprietary lens, basically, you’re gonna need their fitting set. So these fitting sets can definitely take up more space, if your space is limited. So for the purposes of this talk, I’ve mentioned what empirical fitting is, but the purpose of this talk is also to focus a little more on the diagnostic aspect of fitting GP lenses. So the next thing is going to select your lenses. All right, so… The first thing is we need to choose a size and diameter that we want to do. A lot of that is gonna be on the indication. Do we want to do it as large as a scleral lens? Do we want to consider intralimbal lens, or just a corneal lens? For this talk, we’re gonna be focusing more on a corneal lens. Of those three aspects, do we want a large diameter size or smaller diameter size? So for the corneal GP lenses, I’m gonna be talking about the large diameter and small diameter, but again, depending on a corneal lens, you can go upwards to 10 to 11, which might even be considered intralimbal, and you can go as small as an 8.6, so it can definitely range. What we need to consider when we’re choosing the size of diameter, one of them is gonna be the corneal size. How big is that cornea? The larger the cornea, the larger you have to make that lens. The pupil diameter. The larger your pupil might be, during certain situations, the larger the optic zone might have to be. Therefore that might affect how large to make the lens. The horizontal visible iris diameter and the palpebral aperture size. Small eyes. So for those of you in the Asian areas, as me being Asian, as you’ll recognize, our HVID and upper pupil apertures tend to be a little bit smaller. So putting a bigger sized lens might be a little more difficult to get in the eyes. And palpebral aperture size might influence how that lens will fit. So you need to take that into consideration. Blink status and lid tension. Does the patient have a proper blink, and is the lens tight enough that it might make the lens too tight or not enough in those cases? Corneal condition and location and severity of the disease. Where is this condition? In a normal cornea, you don’t necessarily have to worry about that as much, but in an irregular cornea, keratoconus, do we have the cone more of a central, or is that cone actually more inferior? Because that high cone will dictate where that lens is gonna be, and we may need to estimate the size to find a more stable area. And the tear film status basically, too. Do we have a particularly dry patient? In which case maybe a scleral lens might be a little bit better, so we can provide the fluid in that scleral lens. We’re gonna select your design from it. So we’re gonna be focusing on the corneal lenses. So of the corneal lenses, do we want to aim for a spherical GP? Both the front and the back surface have a spherical curve. A front toric GP lens. So the part of the lens that’s gonna interact with the cornea — that will be a spherical curve. But the front surface will have a toric curve for residual astigmatism. Do we want a back surface for our lens? That will have a back surface with a toric curve, two base curves, and the front surface will be spherical, or bitoric GP lens? A GP lens, corneal lens, that has both the front and the back surfaces have two curvatures? And then also the design of corneal lens… We have multifocal and ortho-K lens, and then also to a certain-degree, we can consider hybrid lenses. But the last three we’ll not be discussing for today. All right, so select your base curve. To get that, first we need to have some information. So now the question is: Keratometry or corneal topography. Is there a right answer? Not really. Some of us will not have the technology for corneal topography, so we have to go with keratometry. Keratometry has been the gold standard for quite a while, and there’s nothing wrong with it. One argument of keratometry, why we shouldn’t use that, is that keratometry is very limited. For a smaller diameter lens, we may not have as much of an influence as you go further out, but as you do go further out, especially in irregular conditions, there might be a lot more irregularities that our keratometry might not pick up, that our corneal topographer can pick up, basically. One of the questions we had at the registration was… Oh, what is the best way to fit lenses, without Ks? When it comes to regular corneas and irregular corneas, I don’t know why there should not be a reason to not have Ks. But understandably, there are gonna be, say, some practices that only have an autorefraction that does autoKs. Doesn’t give you a reading. Or might not have the best readings. I don’t know if there’s a best way to fit them without a fitting set, but if you have a fitting set, in terms of irregular lenses, one of my mentors basically at the beginning of the pickup of the scleral lenses, they started getting a little bit better, and these nomograms started coming up. Basically his advice was: If you don’t know where to start, look at the surface of the cornea. Does it look like we’re dealing with a cornea that is relatively high, meaning a steep cornea that might be from keratoconus, or does it look normal or relatively low? If it is on the higher side, pick a steeper lens. If we don’t need something on the steeper side, randomly pick your middle lens in the fitting set. You put that on, you can see what the fluorescein pattern is, and from that, you can bracket it. If you see a lot of fluorescein, you know it’s steeper, and you can pick a lens that’s a little bit flatter. Too much touch, you can pick another lens that’s steeper. So it’s not the most efficient way, but when in doubt, you can still get the information that you need there. So here is basically a fitting philosophy of how to choose the initial lens base curve. Now, this is just one of many ways of deciding a base curve. I did take this out of one of the references. One thing I forgot to mention in the beginning is that: My intention is, as I get later on into the talk, any of the pictures and graphs that I have taken, I’ve taken directly off of the internet, so that anything — so for those of you who want to look back, these should be relatively easy for you to get. We’re all on the webinar, therefore we all have internet access. Hopefully you’ll be able to look this stuff up again and reference it. One thing that I was a little bit… I don’t want to say discouraged or disappointed about, but as I was looking for references, there weren’t as many references online as I would have expected there to be. And it does kind of make sense, because GP lenses are starting to become less popular, but the amount of information, photos, and videos that I was expecting to be available to us was not there. So this is just one of those philosophies or nomograms of how to choose an initial lens. So you’re basically basing it off of your corneal keratometry or corneal topography, depending on the size what you want, whether you’re going a little bit lower. I have this as a 9.0, but you can go down to an 8.8. If you want to go that small. So if you do have a cornea that had 1 diopter of cyl, and you wanted to fit a 9.4-diameter lens, the initial lens you’re gonna do is you’re gonna pick your diagnostic lens that is 0.25 diopters flatter than your average K. If you’re going with more cyl, say a 2.0 diopters, in corneal cyl, and you want a little larger lens, maybe a 10.0 lens, you’re gonna fit that on average K. And if anything is greater than 2.0 diopters, generally you’re gonna go with a toric base curve. A bitoric, front surface toric, or back surface toric. That is to be determined. One thing you have to remember when we are fitting these lenses is that the cornea is an aspheric surface. This is why corneal topography sometimes works a little better. At the central 3 millimeters, you’re gonna get a certain curvature, but as you go out, it’s gonna flatten a little bit more. As it flattens out, every patient is a little bit different, but on average, the central eccentricity is gonna go from 0.3 to 0.7. It flattens going from the center to the periphery, and it may be toric. And it is asymmetrical, basically. So in talking about the base curves, like I said, there are the back surface toric lenses. Again, here’s just one nomogram of a philosophy that — of how to choose your base curves. In terms of all these philosophies, I don’t think there’s one right or wrong answer. One recommendation I would make is, if you pick one philosophy, try to stick with that, so that each time you’re doing a process, you do it starting from a standard point, and you can work off of that a little bit differently. My personal philosophy when it comes to back surface torics is this is where I will go with an empirical lens, basically, too. So I’ll find what the curvatures are, call up the lab, and let them design it. I may go to the point of figuring out whether I think it should be a back surface, front surface, bitoric, and I might even calculate what that bitoric lens is, if I’m gonna go over this next slide. But in terms of that lens, I would usually go empirically. Another reason also to go empirically is I only have a fitting set that has spherical curves. So I would put the spherical lens on and I have two curvatures. I have to put twice as many lenses on to possibly get the measurements I need for those two curvatures, which I find is not gonna be as efficient chair time. If we do determine that we need a bitoric lens, this is one of the more common kind of calculators. If you want to, to a certain degree, say you’re gonna order it empirically, not lab designed, but your own design, this is the Mandell-Moore bitoric calculator. Textbooks talk about this a lot. It’s available online. This is just based on your keratometry readings. You plug the numbers in, and it will come up with the base curve and the power for each meridian, basically. All you need to do is decide which diameter you want, basically. Now, I’ve been talking about these curves and I’ve been talking about the base curve, which is the central base curve, which is gonna be on the optic zone diameter. What we often remember is that there’s gonna be multiple base curves. Here’s a picture an example of a typical GP lens which has three curves. You have a base curve, a secondary curve, and a tertiary curve. You may even have certain lens designs where you go to a fourth curve too. Most of the time you’re gonna be basing it off the central base curve, but if you need to customize earlier, you can specify your secondary base curve and your tertiary base curve. Usually they are gonna be a little bit flatter. When you order your lenses, like I said, most of the time they’re just gonna send it to you with the base curve and a standard secondary and tertiary curve in their nomograms, but if they needed to specify the width of these curves and the size of the curves, you can specify that, to get that fit even more precise. The other things also — knowing that you have that base curve and the secondary peripheral curve, you can also order those as a toric curve, basically, too. Also, in choosing our lens, not necessarily for the fitting process of the initial lens, but when you order the lenses, after the diagnostic, you need to choose your material basically, too. Do we want a silicone acrylate lens, or a fluoroacrylate material? Each one of those has different properties. Based on the durability, the stiffness of that lens, each one of those has different permeabilities. So whether you want a higher dK or lower dK lens. Higher dK will have softer materials, and lower dK will be stiffer, compared to the higher dK lenses. So you might have to worry about flexure, and might want to go with a lower dK lens, something with a stiffer material. One more thing about the silicone and fluorosilicone acrylates. They have different surface properties, so that may play a factor, as well as the wettability. The surface coating and the way that the polymers are manipulated to handle the wetness. Remember, plastic by nature does not hold water, so if you were to take just the raw plastic and add some form of fluid, whether it be saline or your natural tears, it is not gonna adhere to that contact lens. So they do have to manipulate it, to draw it into the matrix of the contact lens. As well as there are gonna be even newer technologies now where there’s gonna be a surface coating or treatment. So whether there’s a plasma treatment to the lens, to make that surface a lot cleaner, or a new thing that’s in the United States, tangible Hydra-PEG, which draws water to the surface, you have all these options when you order this lens. Examples of materials. These are in the United States. Some I know are international. You have the boffin Brand, Optimum Brand, Paragon Brand, Fluoroperm Brand, and Menicon. Different lenses. Not necessarily a right or wrong answer as to what material you choose. So now the fitting process. We’ve decided on the approach we’re going to. Now we have to put the lens on. Whether this is your empirically fit lens, already made in the lab, or the diagnostic lens, now it has to get on the patient. So poll question number five is: Do you use anesthetic during the fitting process? One yes, two no. All right. So a majority of you said yes. About two thirds said yes and a third said no. This is an ongoing debate, and there is no right or wrong answer. My personal philosophy is I don’t like to use anesthetic. Basically I’m a get to the point guy. I want to put that lens on. If that patient can’t stand it, I want to know that in the beginning. That might help my decision as to whether I want to continue in the GP process or say… All right, no, I don’t think GP is gonna be beneficial. When it comes to the lens itself, in terms of troubleshooting, sometimes I want the patient to be able to feel the lens and say this is what is going on, so I can troubleshoot it a little bit more. If I’m doing, say, hard contact initially to see if GP lens might work better, I might put anesthetic, but for the majority, I don’t use anesthetic. Whether are you using anesthetic or not using anesthetic, you have to let it settle in. You’ve got all the fluid from the tears and the conditioning solution. That is going to cause the lens to settle, at least 10 minutes, or a little longer. That’s when efficiency comes in. That 10 minutes is time that your patient is in the office, possibly in your chair, so that’s where we need to debate if we need to be more efficient, where we might need to cut things down. We’re gonna measure the visual acuity, perform overrefraction. My personal thing is to refine it with the phoropter. But sometimes the phoropter can make you do things differently that can influence the way the lens is sitting. We’re gonna evaluate the central fluorescein pattern, the midperipheral fluorescein pattern and peripheral edge, and then modify as needed. Now we’ve got it on, it’s settled in, now we have to look at the lens. In general, this is what a textbook fluorescein pattern should look like that’s aligned. As you can see, we have pretty much the fluorescein. There’ll be some on the surface, and one of the tricky parts about fitting GP lenses is what is on the surface and what is underneath the lens. But it’s typically uniform all the way across. We know that the thickness of this tear is pretty much the same. Remember, the higher the concentration of fluorescein, the brighter it will be. The less fluorescein or no fluorescein, the darker it will be, or a black spot. So in this particular case, you have a relatively uniform fit. If you notice here, one of the sources I got this from was GPLI.info, which is on the internet. At the end, I’m gonna go over some resources, but this is where I got this picture. So you can refer back, and they’ve got other pictures that are useful if you want a reference guide. I know some practitioners that have copied that, and they have it on their desk, so if they want to look at the computer, it’s right there. That’s an aligned fit. The curvature of the back surface of the corneal curvature matches pretty much closely to the front surface of the cornea. Now, here are two examples of flatter fitting lenses. So the curve is less than the curvature of your cornea. So here this is about 2 diopters flatter. You can see here in this particular area where it’s particularly dark. You’ve got touch there. There’s no fluorescein under there. Direct contact to the cornea. And as it goes out, it is then in essence steepening, or the fluorescein has accumulated a little bit more. Here is one diopter. So not quite a large area. Generally the touch pattern is right around there. So the touch pattern is a little bit — basically the lens is riding more on the center. All the pressure of the lens is riding more on the center here, spread out a little bit more there, in that particular lens. Now, we’ve got two flatter ones. These are two steeper ones. So in the flatter ones, no fluorescein underneath the lens, dark spot, steeper one, fluorescein under the lens, lighter spot. Here because it’s so steep, they have an air pocket underneath it. You can see it’s steeper here and because it flattens out because of the way it interacts, you get more bearing there. That’s your classic too steep of a lens. Here it’s more 1 diopter steep basically, too. So you have a little bit more… Not quite as high a concentration. It does spread out a little bit more, but we still have that bearing there, which is indicating that the lens is still riding too high over the center. So another question I got in the registration was: Is it better to fit steep or loose? The reference was in irregular corneas, but I think it’s just a good general question, whether it’s a normal cornea or irregular cornea. There’s no right or wrong answer for that, basically. I think it really all depends on the situation. If you’ve got good interaction with the cornea, but the lens is a little more comfortable, and you need to steep it up a little more for comfort, put it a little bit steeper. If anything, I would probably say my personal preference — or if you looked at all my lenses, it probably is a little bit more on the steeper side. My thing is I try not to influence the cornea as much. So with a keratoconus, fitting right on that cone and actually fitting it flat might benefit the vision a little bit more, but studies have shown that contact might cause more scarring and more changes to that cornea. So I typically will go more on the steeper side, but fitting flat is not necessarily gonna be a wrong answer either, provided we take other things into consideration, and it doesn’t influence the overall health of the cornea. This is just an example of what a spherical lens would look like, over a toric lens. So you have bearing here, where the curve is flatter than the cornea. We have a lot more pooling here, because the curve is steeper than that too. So this is just something to keep in mind. This is your textbook there too. So if you have a derivation of that, or what we call that classic bow tie pattern, we can guide you as to how much you might need to change that lens. In this case, we might want to go with more of a toric base curve. So here are three kind of general pictures of lenses to demonstrate, one, the location of the lens, but also determine whether it’s an interpalpebral or lid-attached. Lid-attached just basically means you’re using the lid to hold the lens up. The position of the lens is influenced by the use of the lid. Interpalpebral, not as much. If you were to take the lids out of the equation, lift it up, your lens would stay and interact the exact same way. So this picture here — for the fit, I would document it as more of a superior fit. Because it is sitting more on the cornea. But it is also a lid-attached fit. If this was a video here, what you would see is that when the lid blinks up and down, the lens would follow with it. Here you can see the edge is a little bit higher, so you know that edge is gripping a little bit more underneath the lids, so it’s gonna be, again, interaction with that. Here is more of a central fitted with the lid attachment too. So you get more of a uniform corneal exposure there, so it’s more centered. The edge is still a little bit on the higher side here, so you know it’s gonna be pulling it up and down, basically, too. And here’s more of an inferior fit. That lens is fitting more clown close toward the inferior limbus. If you took the lids out of play, it’s not here. With this picture, you would not be able to tell — if somebody asks me how do you know it’s interpalpebral. The two indications that would make me suspect it’s interpalpebral is that the edge lift is very thin. So the lid’s ability to pick that lens up may not be as great. One thing we don’t know about this lens is the power and the shape. This might have a lenticular lens that might change that interaction, but looking at that curvature there, I would suspect it’s probably not interacting with the lids. The other thing also, in a motion video, if I were to then take this and pull this little way, that lens is gonna stay exactly the same place. Versus if it was lid attached, what would happen is that lenses which are inferior may drop even more too. So it’s not being influenced or being held up by the lids. All right, so I apologize here. My intention was to have some videos of typical movement of lenses, or my video was corrupt, so I couldn’t get it in, but in terms of trying to get some new videos, I wasn’t able to get any new videos. My intention here was to show you what an aligned lens looked like, where it’s basically uniform, and as the lens blinks, you’re gonna see typical up and down, relatively smooth movement. Lens goes up when the lid is attached, lens goes down, basically. So it’s uniform up and down. If you have a steep lens, you’re still gonna have the up and down movement, but it typically is gonna be more of an up and quick motion down, almost as if — it’ll be straight up and down. Basically the description is almost as if it’s riding on rails, and the reason for that is that the lens is steeper. Usually your peripheral curves are gonna be steeper, so it’s riding on the edge of the peripheral curve, not the back surface of the cornea, so it’s gonna go up and down. Compared to a flatter lens, which is gonna be typically straight up, but actually rolls down. You go up and it will have a rolling effect. And the reason for that is what we call the teeter-totter effect. Because it’s flatter, it’s not resting on the edges of the contact lenses. It’s actually resting on the center. So it’s kind of having a wobbling effect, kind of a saucer over a divot. So it’s just gonna kind of roll, have that rolling sensation. Again, I couldn’t find any good videos online. I believe GPLI does have a couple of examples of that, if you do want to see that. But I think for most of you who have fit lenses, you do kind of know what I’m kind of describing. All right, so now we’re gonna talk about the edge lift and comfort relationship, basically, too. So as we are looking at that lens, we saw through those other pictures, they can have a smaller edge, smaller, lower, or steeper fit, and a flatter one that comes up a little bit more. So that low edge profile is gonna be a little bit dependent on the patient. If we call a moderate edge lift, basically what we’re saying is it’s probably causing the best comfort. And again, this is all relative to the patient basically, too. Some patients may require a lower edge lift, and some may require a higher edge lift, but if you can say that edge lift is doing what I need it to do, and it’s facilitating good comfort for the patients, it may be considered moderate. If you have a low edge lift, you see less fluorescein underneath that edge, if it is causing problems, generally it’s one where the patient says: I feel the edges on the cornea. It feels like it’s scratching on my eyes or near the limbus area. And with the lower edge lift, sometimes it may be easier to get an interpalpebral there too. If you want interpalpebral, you want to make that edge lift a little lower, or if the patient is describing that feeling, that means that the edge is a little lower. On the opposite side, if you have high edge lift, this is typically gonna be on a symptomatic purpose. The patient says they’re gonna be feeling it on the eyelids basically, too. And then also with a higher edge lift, though, you may want to put a higher edge lift to make it so that it attaches to the lid a little bit easier. If you tuck it underneath the lids, is there area for the lid to grab to? To make an area for lid attachment. So now we’re gonna go to troubleshooting. We might have to go through this a little bit quicker than I was expecting, but troubleshooting and modifying and adjusting the fit. If we have a lens that’s too flat, again, what you’re gonna see in those previous pictures is the apical bearing. So the possible changes to fixing this is obviously to steepen the base curve of the lens. But you don’t necessarily want to steepen the base curve of the lens, we can increase the overall diameter of the lens. By increasing the diameter of the lens, that effectively steepens up the lens diameter. So what we have to remember is that approximately 1 millimeter change in diameter will change the base curve by an equivalent of 0.1 millimeters basically, too. So whether you’re using a smaller diameter lens, this may be a way you might say… All right. I don’t want to change the base curve. Let’s make the diameter a little bit larger. If you have a large diameter lens, and you don’t want to change the base curve, you can just change the optic zone diameter to get the same effect. If the lens is too steep, again, that’s when we have that apical… Sorry. Go back. Sorry, that should be — that is a misprint. That should actually be an apical clearance. You’re gonna see too much fluorescein underneath it. So the possible changes there are flattening that lens, flattening base curve. Or now doing the opposite. Decreasing the overall diameter, or decreasing the optic zone diameter. Changing those effectively flattens the lens out. So a 1 millimeter change in diameter will make a 0.1 millimeter change in the base curve. That would be another approach there. One thing we also have to remember, while we’re doing this, is even though when we change the lenses, we are effectively changing the power of the lens. Why? It’s that there is — the lacrimal lens, there’s the tears between the lens back surface and the corneal front surface, which is creating that lacrimal lens, which does have corrective power. And that corrective power is based on the curvature of the front surface and the front surface of the cornea and the back surface of your lens. If you have a steep base curve over flatter cornea, you actually have a lacrimal lens that’s giving you a plus power. If you have a flat base curve over a steeper cornea, you actually have a minus power lacrimal lens. One way to kind of conceptualize is: If you draw it up, so if you think of a flat cornea, draw a line. If you think of a steep base curve cornea, put a curve on top of that, meaning that the curvature of the lens is steep. What you have there is what looks like a convex lens. That’s gonna give you plus power. If you were to take a steeper cornea, that cornea, instead of being a flat line, you’re gonna make it a round circle. A steepness to it. But the lens becomes flat. Make that the line. Now, if you make that the lens, what you’ll see is you have a thicker edge, or it’s a concave lens. That’s where you get your minus power from. We do have to remember, when we take this into consideration and make our changes, we have to consider what we call the SAM FAP rule. Steepen, add minus. Flatten, add plus. When you steepen the lens, you have to add minus power to the lens to compensate for changing the lacrimal lens. The appropriate power is: For every 0.1 millimeter change in base curve radius, it’s gonna be approximately a half diopter change in power. So if you steepen a base curve, half diopter, steepen a base curve by 0.1, add minus half diopter. If you’re flattening it, as plus half diopter. And this would be accounted for when you’re changing the diameter or the optic zone diameter, because again, you are effectively changing the base curve power. So here are the fitting pearls to remember, that we just went over. Steepen the base curve steepens also the peripheral curve, because the peripheral curves are usually based off of your base curve diameter. If you do not want that to be changed, that is when you have to specify with your lab to change the base curve, but to keep the peripheral curve in the same reference point, which you were having for your diagnostic lens. Flattening the base curve flattens peripheral curve. Increasing the lens diameter will also increase the edge lift. You are increasing the lens diameter, therefore increasing or steepening the lens, therefore it’s gonna bring that edge lift down, and decreasing the lens diameter will decrease the edge lift. And changing optic diameter will also influence the fit. So now if you have a lens that has no movement, or it seems that the lens is too tight, what you might see is gonna be a static lens. That lens is not necessarily centered, but sticking to exactly where it is on the blink, and not moving. And there might not be much appearance of any edge lift, and generally, if it is really sealed off, there won’t be any fluorescein underneath it, or if it’s really too steep, the fluorescein you get underneath it will be relatively high. So to fix this problem, what you can possibly do is flatten the base curve, because that will essentially flatten the entire lens and bring it down. You can decrease the overall diameter, decrease the optic zone diameter, or just keep the base curve diameter the same, but flatten the peripheral curve. Remember, the peripheral curves are kind of more where sometimes where the lens is riding on, so also by lifting it up, think of a tripod. A camera tripod is three legs that meet — that are at an angle, that meet up at a certain point. If you were to have all three legs parallel to each other, up and down, you go to have that… Whatever the camera on that tripod at its highest point. If you take those three legs and you flatten them so they’re all parallel to each other, now you have the camera at its lowest point. So if you want to raise things up a little bit, effectively, you’re gonna bring those legs down and steepen up, or if you need to bring it down a little bit, you flatten them out too. That works for hard lenses. It’s a key concept in scleral lenses. And it will also work for much larger diameter lenses. Excessive movement or lens drop. So when you have this, though, we do have to determine what the reason is for that. So is the lens riding too flat? Is it gonna have that rolling thing? If it’s just too flat, steepen up that lens. The base curve-cornea relationship. Is the lens too steep? You’ve got that up and down? That’s where we’re gonna flatten that lens. Do we need to achieve a lid attachment? It’s just moving around and we have an interactive lens? It will stabilize itself? Change the curve/edge lift to have a little bit more interaction. Increasing the diameter is another option to improve stability, just making that lens a lot bigger. Part of why I like that a little bit more is that my philosophy is I try to interact where I know it’s gonna be less likely to be irregular, and typically, at least if you go out to the conjunctiva, it’s gonna be less likely that there are gonna be issues there. That’s the reason I happen to like scleral lenses. But the larger you go out, the more likely you might get to an area where it’s less irregular. Take something like pellucid marginal degeneration, that might not necessarily work, but in general, that’s why I like making the lens a little bit bigger. And is that lens too high a prescription? If it’s too high a prescription, is there too much mass on that lens, that’s making that lens just drop? So one other thing that you can specify in the lenses are lenticular — lenticulation. In this case, this is minus power lenticulation. One of the advantages is that it is basically creating a thicker edge. On a low minus, any plus lens, it tapers off to a thinner edge. This will put a thicker edge on it, basically. Your front optic zone is gonna be equal in size to your back optic zone, basically. And you can have a plus carrier lenticular, which is the opposite. If you have a high minus lens, where the edge is gonna be thicker, your plus carrier lenticular is gonna thin it out. It will decrease the edge thickness, which may decrease awareness, but also since we’re taking out material, it will decrease the mass of that lens. Is the lens decentered? You can increase the diameter on that and steepen the base curve and/or the peripheral curve. Poor vision. Everything might be great, but the patient might say: I can’t see out of it. We have to do a little troubleshooting. That’s gonna be a little easier. Could it just be incorrect power? Which you can determine from overrefraction. Is it poor surface wettability? When you first put a lens on, the most common problem for that poor vision is that a lot of the times the lens is not wetting properly. And it’s because during the manufacturing process they use what we call a waxy pitch to hold it on the lathe. They try to take it off, but sometimes they don’t get it 100% off. It’s a waxy, wooly substance that will repel water. Sometimes just cleaning that off will help that issue. If the lens is improperly positioned, you may not be getting to the proper optic zone so you may not get the full power or optic power you want. Optic surface may be dry. Are you getting dryness from the conditioning solution? Because the eye is so dry, there’s no effect of the lacrimal tear? Lens flexure. Is that lens warping on the eye? Is the cornea toric enough that it’s actually causing that lens to bend? And in an older lens, is it permanently warped, basically, too? So those are things you can look at, to troubleshoot, when it’s poor vision. If the vision is good, but the lens is uncomfortable, one of the things that we can do to try to improve that is decrease the lens movement. So maybe make that lens a little more lid attached. We can modify that edge a little bit too. Possibly thinning it out or rounding it. In the olden days, we used to do that ourselves. Now you can specify it from your lab. Modify the curve junctions. As I showed you in the picture with the three curves, each one of the junctions is gonna have a transition. That transition can be blended. It can be a rough edge or sharp transition, or you may have to ask the lab to blend it. You may have to ask them to blend it even further, if there’s patient sensitivity to it. We can lenticulate the lens, and we need to take the ocular surface into consideration. Is there enough fluid to cushion that lens, basically. The next one I’m gonna go over, just because I’m running out of time and I want to have time to get to some questions. In the overall process of the fitting, we need to take the lens care and follow-up into consideration too. So in addition to fitting these lenses, we need to make sure to educate them on how to properly clean these lenses. The daily cleaning and conditioning maintains the lenses as comfortable and reduces lens-related problems. Here are two examples of cleaning solutions, the Boston cleaning solution and conditioning solution, as well as separate cleaners. Depending on what you have in your country, you just need to make sure whether it’s at the initial — all right, happy to try out the lenses, or even on subsequent follow-ups, we need to reinforce the aspect of cleaning the lenses and stressing good lens hygiene and even replacement of the lenses, not to let the lenses go on as much. So in follow-up, reinforce annual evaluations of lenses to ensure continuous proper fit and vision. And the other thing I consider in my practice is I tell patients to stop back in after six months, and I generally to a semi-annual in-office deep cleaning. Basically that entails taking a laboratory polishing solution, give it a little light polish, to kind of take some of the surface debris off. You don’t want to do it so abrasive that you’re changing the surface, but just enough to give it a little extra friction to it. I briefly rub it with some alcohol cleaner to clean it, and the biggest thing is I give it a Progent soak. Progent is a chemical cleaner, a bleach cleaner, that’s manufactured by Progent. It gets everything nice and clean. So just checking in — hey, how are you doing? Great. I’ll take your lenses, have them back to you in an hour or so, just have them keep up with how they’re doing with the lenses, as opposed to an annual visit, and I charge them $15 for that, just for the cost of the material. And I think patients recognize that — yeah, it’s a good thing if I can have my lenses cleaned a little more, because in the long run, the longer their lenses are preserved, the more they’re gonna save both on buying new lenses, possibly comfort of the lenses, and then if the lenses are cleaner and healthier, less likely to cause any problems. All right, so just a couple of tips and advice. So one thing is, on those pictures, those were with fluorescein, and the image was also enhanced with a wratten filter. So always use the filter and use bright light. Fluorescein is stimulated by bright light, so the brighter your light, the better you’ll see it. Put fluorescein on the lens surface and don’t use a lot. In optometry school, I see students flood the eye with fluorescein. Not necessarily a wrong way, but from my personal opinion, I think for evaluating the lenses, that’s a little bit too much fluorescein. I recommend taking the fluorescein tab and lightly wetting it, and using a paintbrush, lightly dab across the surface of the lens, and allowing the blink to spread it, but also allow it to mix with the tears, so you can see how it starts to travel into — underneath the lens. If it’s too tight, you may not have enough fluorescein in there to get underneath it, to show you that fluorescein pattern. Whereas flooding the eye might actually — it’ll get plenty, and it might be harder to discern whether it’s on the surface or underneath the lens. If available, talk to your consultants at your manufacturing lab. Those of you who are starting to get more into this, newer to fitting GP lenses, your lab should have some consultants that you can talk to. Even if it’s just — all right, I think I want to order this lens, when you go to the next troubleshoot, even if you think you know what it is, talk to your consultant. Say: Hey, this is what I think I want to order. Would you agree? Or would you suggest something different, and then with that dialogue, they’ll suggest why they suggest something different, and that will bring a different perspective, why you might want to make a different change to the lenses. Don’t make too many changes at once. Even if that lens looks terrible, try to make small changes. Maybe change one thing at a time. Whether it’s the base curve or a peripheral curve, but don’t make too many changes at once, because you put too many variables — it’s just like trying to change a recipe, when you’re cooking. If you change too many ingredients, you don’t know which one was the right one and which was the one you shouldn’t have been changing. Just my opinion is that larger is better. As I said earlier, I’m a big fan of scleral lenses and larger diameter lenses, and part of my philosophy with that is: The larger lens, the more area I have that is likely to be stable. If you think of how those lenses are interacting, the more surface area you have, the more you’re likely to get an area that is interacting with a non-damaged or irregular area, and it might be able to interact with a normal limbus or a normal conjunctiva. So my opinion is that larger is better. We also have to kind of keep in mind: There’s no one exact correct fit. Ultimately what we’re looking for is what is in the best interests of the patient. The key thing is vision. As long as you are getting the vision you need and it’s making the patient happy, we’re good there. Comfort. As long as that patient is saying comfort, and at the exact same time, you’re saying the interaction with the cornea and the lens is good, we’re in the right situation. I might say… Oh yeah, I might want to make it a little bit different, compared to yours, but again, as long as we’ve got the patient’s best interest and the cornea in the best interest, again, there can be multiple answers as to what the correct lens size, diameter, material, all that could be, basically. Don’t hesitate to recommend rewetting agents and artificial tears to improve comfort. If everything is good and the patient says I can’t wear it quite so long and you change everything, again, there’s no reason you can’t use artificial tears to supplement the comfort. And don’t forget, you can use a piggy back. For those unfamiliar with the piggy back, that just means using a soft contact lens under the hard contact lens to decrease interaction with the contact lens on the cornea to facilitate better comfort. And along that same line, if it is available in your area, don’t forget that anything you said works well — everything has been pretty good with the GP lens, but I can’t get that comfort better, maybe a hybrid lens will work a little bit better. A hybrid lens is a hard lens with a soft material fused outside. So you get the vision benefits of the hard lens but the comfort of the soft lens. Typically we’ll center it a little bit better and the lid interaction is a little bit less. I’m not gonna say it’s a good indication for everything, but just keeping in mind that there are definitely different options available, basically. So here’s a list of the resources. I believe you have access to this PowerPoint, so you’ll have this there. But the main website I found was the GPLI info. One of the textbooks I used as a manual of gas permeable contact lenses by Ed Bennett and Milton Hom. There are different ones out there. My school uses a different one, so depending on the resources out there, that’s a good one to look at. Two journals out there. Contact Lens Spectrum, they have articles about scleral lenses and irregular contact lenses. So clspectrum.com and reviewofcontactlenses.com. Just to review what you have there. So thank you for listening. There is my email address there. I’m gonna answer a few questions, but if I don’t get to all the questions, basically feel free to email me, and I will be more than happy to answer it. I think I saw on the registration list I have interacted with you through Cybersight. I am a mentor on there, so if there are any questions… I don’t know if you can specifically request mentors, but I’m happy to answer any questions there as well. So we’ve got some questions and answers here. Question one. When the keratoconus position is inferior, it creates more problems with fitting. How to solve it? That’s gonna be a little bit tricky, because a lot of times it’s gonna have to do with the lens itself. Because of the nature of that aspect, you have — just physicswise, you have something… I don’t want to say it’s gravity, but you have something that it’s always going to try to draw in place. You have eventually a convex surface on your cornea and a concave lens. It’s drawing it and locking it in place. Depending on how inferior it is, I’m gonna go with a bigger lens, so if I make it much larger and it’s not all the way down to the limbus, if I can get an intralimbal lens and rest it on the limbus and bring, essentially, the lens up, now it’s not gonna have a tendency to find a high point of my lens and drop down there. It’s gonna be more resting on the edges too. Or go a little bit larger with a scleral. The sclera or the conjunctiva, where you should have more steepening, so everything is vaulting over. It’s dropping because it’s trying to lock in there, but if we can avoid locking it in place, it may not drop as much, basically. I have another question here. Is a very small bubble on the peripheral region of the lens acceptable? Me personally… Generally, as long as it’s not gonna cause an issue. This is one of those things where you may say… All right, I see this peripheral bubble. Let me look at it a little bit longer. If I add a rewetting drop, does that peripheral bubble go away? Or does it seem like it stays? So your concern about the bubble is that, if there’s a bubble there, there’s no tears underneath it, which can cause an area of desiccation. You don’t want the cornea to get irritated and desiccated underneath there. If something is inconsistent but it’s not causing any health issues to the cornea, I would not be concerned about it. If it is causing some desiccation or it’s one of these things where you say: I fit this contact lens today, and it’s there. When the patient came back for the fall visit, it will still be there. If it’s inconsistent, you might be concerned about it, in which case you might want to look at interaction, by bringing the lens down a little or bringing that curve down a little bit. May essentially relieve some of the extra space and bring it down. Or you might, if it’s too much space, you might have to change this in terms of the size of the curve itself. What is the main disadvantage of RGP lenses? I would say I don’t necessarily… I wouldn’t say there is a disadvantage from my purpose of looking at it from a doctor’s perspective. From a patient’s perspective, basically, their views might be… Well, it can be a little bit more uncomfortable, compared to a soft contact lens. With some of the more common used soft contact lens, oh, I have a monthly lens. I can replace it in a month. When I buy it, I have several lenses, so if I lose it, I have a little more. The fact that you might lose the hard contact lens is a disadvantage, basically. How to measure lid tension? I personally don’t know how to answer that exactly. A lot of times what I’ll do is I’ll just… Hold the lids and kind of look at it, and just kind of pull to see… Compared to some of my other patients, does it feel like it’s a little resistant? When you’re doing your assessment, one of the things you should be doing at some point is looking underneath the lids, so when you flip that lid, sometimes you get a sense of whether it seems floppy or it’s a little tighter. And sometimes I’ll ask them to blink. If they close their eyes and blink, you can get a sense of whether it’s gonna be a harder blink or a softer blink. But giving you an exact measurement — that I don’t have an answer to. Are some bubbles allowed if it’s mobile? I would say you don’t want a whole lot of it. It all depends. If the bubbles are short lived, that should be perfectly fine. If the bubbles aren’t short lived, then I try to get rid of those bubbles. So if you can, try to get rid of them. But taking the whole thing into consideration, if it’s not necessarily affecting the health of the eye, or affecting the quality of the fit, then it may be okay. What to do in the case of 3 and 9 staining? Generally that’s just gonna be modifying to fit a little more. If I can modify that edge, I’ll try to modify the edge. That’s again where I might say: Hey, what happens if I use artificial tears? If I can solve the problem with the artificial tears and the patient doesn’t mind, I might do that. But it depends on what I see with the interaction of the lens, the corneal relationship, the degree of how much staining it is. What conditions where RGP are contraindicated? There’s probably several of them there. Like I said, it really all depends. One would think: If you have a corneal transplant, why would you want to put a lens on that transplant, where you have potentially open cornea? You have a risk for infection? But we do that, basically, too. So I think it really is… Are there any underlying factors with the eye itself? Not necessarily the condition, but are there any underlying factors that would make this GP interact, based on the surface — that would put the eyes at significant risk, that you would not want to put them on? But generally usually you’re gonna have other indications, like all right, corneal transplant, I might not want to put on there, but to get the best vision, you still might need to put a corneal GP lens on. Let’s see. Is there a descemetocele, what should be appropriate fitting? That again all depends on what’s going on. Not necessarily a correct answer as to what it is. Just how it’s interacting with the cornea. Slightly inferior fitting is acceptable if it’s covering pupil? I mean, fitting it slightly inferior is acceptable. I guess when we say cover the pupil, as long as the optic zone is there, and you get the proper optics, it is. But sometimes I’ve had patients that I want to bring that lens up, but comfortwise, they didn’t like it. I just manipulated that lens so that when the lens is sitting the way it is, it is the correct optics and everything is working well. But should I change it and bring it up and center it? It might not be 100% appropriates, because you don’t have the appropriate optics, basically. I am running out of time. Let’s see if there are any other quick questions here. All right. If some patients are sensitive or allergic to fluorescein, what’s the other option for static fit evaluation? Well, in that aspect there too… Again, what we have to ask ourselves: Are there any other dyes, basically? So what you’re just trying to do is look at the influence of the tears underneath it. So if you can dye it with either lissamine green or rose Bengal, probably not the most optimal. You can use that. Talking about the technology, sometimes if you want to look at static, but can’t put any dye in it, another thing you can do… Just thinking outside of the box… Is you can possibly use anterior segment OCT and use that to measure that. I use an anterior segment OCT to evaluate my scleral vault, so why couldn’t you use that for GP lenses? But I haven’t run into that situation where I had to go that far. If I really needed to, I would use lissamine green to put that in, basically. I don’t understand what this question about cases should be managed with RGP… Keratoconus? If the situation arises, yep. I will do that with an RGP. But I will think that there’s other options. We do have certain soft lenses that are available. I won’t necessarily go with that. But a scleral lens I will go with. Patients for RGP… So I have a patient prescribed RGP lens, but the manufacturer made the lens in a different calculation as I did before. Different brands have different calculations? So if you are using a proprietary design, then yes, the lenses are different. However, if you are specifying a GP lens, the peripheral curves from manufacturer to manufacturer might be a little bit different. However, you might not necessarily need to… They will be different. So if you specify it and change it, so if you know I ordered lens from A, from lab A, but lab A has since no longer been in business, can I go to lab B? You order the same base curve, you order the same diameter, the same material, everything is the same, but the peripheral curves might be different, based on that lab. So that’s where you might have to specify a different… Tell the lab exactly what you want. I have had a couple patients where that has happened. I had a patient — I prescribed their position, but they didn’t tell me the lab, so I ordered through my lab and it didn’t work quite as well, so I had to order what I saw on their habitual lens and try to tell the lab how I wanted to change that, that was different from their peripheral curve too. So like I said, if you have any other questions, feel free to email me. I’ll be happy to answer. For those of you on the East Coast, have a good rest of the day. For those of you in the rest of the country, I think it’s evening, so have a good evening. Thank you so much.

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September 19, 2018

Last Updated: October 31, 2022

2 thoughts on “Lecture: Rigid Gas Permeable Lens Assessment and Fitting: It’s Not That Hard”

  1. Thanks for giving this lecture, you summed up 3 months of studying RGP fitting pearls into an hour and clarified much of my overthinking! I will search out more lectures before my NCLE test.


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