Right Tools for the Job: Astigmatism Accuracy

Gary Wörtz, MD, sits down with Sumitra Khandelwal, MD, to talk about posterior corneal measurements for toric IOLs and the most accurate tools for acquiring information. Dr. Wörtz also speaks with John Berdahl, MD, regarding astigmatismfix.com, a tool to help surgeons correct residual astigmatism caused by common measurement deviations.

Speaker 1: Ophthalmology off the Grid is supported by Ilevro from Alcon.

Gary: Open. Outspoken. It's Ophthalmology off the Grid, an honest look at controversial topics in the field. I'm Gary Wörtz.

When you're picking a lens for your cataract patients, toric IOLs are a much-loved option. However, the process for selecting the appropriate lens can be complex, especially when you're working with multiple measurements from different devices. To start off this episode of Ophthalmology off the Grid, I interviewed one of Baylor's great ophthalmologists, Dr. Sumitra Khandelwal, to hear her thoughts on posterior corneal measurements and which tools are best for acquiring the most accurate information.

Gary Wörtz with Ophthalmology off the Grid, and today we have with us Dr. Sumitra Khandelwal. Sumitra, we're really excited to talk to you about your practice and the expertise that you bring to toric IOLs and especially posterior astigmatism. Before we get into all that, I'd just like you to give us a little bit about your background. Tell me a little bit about your training, and we'll just go from there.

Sumitra: Sounds great. Thanks, Gary, for having me here on Ophthalmology off the Grid.

I had some fantastic training. I started out my residency at Emory Eye Center in Atlanta, Georgia, and then went on to do a cornea fellowship at Minnesota Eye Consultants with Dr. Lindstrom, Dr. David Hardten, Dr. Tom Samuelson, and Dr. Liz Davis. Now I am incredibly lucky to be at Baylor College of Medicine as Assistant Professor. I work with some excellent colleagues, including Dr. Douglas Koch, Dr. Mitch Weikert, and Dr. Li Wang, all of whom have done much work in the arena of toric IOLs and posterior astigmatism.

Gary: Well, you've absolutely trained with the best people in the world, and so it's exciting for me to get a chance to, even on this interview, to learn from you and to hear what makes your practice special.

The Baylor nomogram and all the research that's come out about longer eyes, actual myopes, I just get excited whenever Baylor puts something out, because it really moves the needle on outcomes. We're all very curious as ophthalmologists, as cataract surgeons, how do we get better? How do we take our results from where we're doing okay, but we always are striving to do better. It seems like Baylor, along with some other institutes around the country and around the world, really has been moving the needle forward. I'm just really excited to talk to you about all of the tools that you use.

Let's start a little bit with talking about when you have a cataract patient who comes into Baylor, what kind of measurements are you getting, and what kind of devices are you using to get those accurate measurements?

Sumitra: We definitely strive to do the best for our patients. Even though there is some great biometry and great topography out there, we still believe in measure multiple times and measure with multiple devices. We don't go with just one or two devices. We're very lucky—Dr. Koch is a big advocate of patient outcomes, and, therefore, there are really many toys and many tools that we can use at our institution.

Currently, for most of our cataract patients, we are using biometry data. We do like the Lenstar because of its accuracy, especially with low amounts of astigmatism and how many measurements it can take for us, plus the ability to throw out some of the standard deviations with them. We definitely teach our technicians to look at the image carefully. It's very easy just to say, "Oh, these are the Lenstar measurements," but you have to have an active role and really work with your technicians to do that.

In addition, we've got some great topographies. We are currently using the i-Optics Cassini for the anterior curvature, and it does provide some information about the posterior cornea as well. We're using Ziemer Galilei as well. We really like the fact that it's got both the Placido image as well as a Scheimpflug image. We use it for both cataract surgery but also for looking at some of the Placido image, maybe catching some subclinical anterior basement membrane dystrophy. We have two printouts that we do for the Galilei, one that has the general total corneal astigmatism, the anterior corneal astigmatism and posterior corneal astigmatism, but a different one that actually prints out the Placido in a very large format so that we can catch any subtle EBMD, any subtle areas where the mires are not accurate.

We used to use other topographies as well that are fantastic topographies out there. We limit it to these three because we feel like that's better for our clinic flow. Of course, we've also got the ORA available for us, intraoperatively, if we need it as well.

Gary: Well, I think those are just amazing devices. I agree with exactly with what you're saying, that measuring multiple times with multiple different devices allows you to have that confidence, especially when all of the numbers agree at least within certain tolerances.

Tell me a little bit about those cases, because we all have them, when we do multiple measurements with different devices, and we get different data. Walk me through your process when you go through trying to pick a lens or trying to determine if your lens calculations are accurate. When they don't all agree, what device are you really looking to be your tiebreaker, so to speak?

Sumitra: Well, with three devices, you definitely can get three different measurements depending on the cornea. I take a step back and try to figure out why I'm getting that. For low amounts of astigmatism, sometimes the magnitude is difficult, so it may help to remeasure, but it may actually help to split the difference between the axis. I sometimes expect the axis to be very different, but those are also patients that you're rarely treating their astigmatism.

For patients who where we're going to treat their astigmatism, or at least address it, it sounds, after all this electronic stuff that's out there, all this great technology, I take a pen and paper and write down the values because I don't want to get too bogged down by the details. I write down the magnitude, and I write down the axis. It'd be great one day if somebody can talk to all of the machines and have an EMR service that actually prints that all out for you, but for me, I actually just write it down and look at it.

I look at the magnitude first and look at where the trend is. I sometimes do also get the IOLMaster as another opportunity to just measure something for our toric patients, but not always. I look at those numbers, and I really have liked, actually, we've used the i-Optics Cassini, and I've actually very much liked the magnitude for that. It's really been very accurate as far as that goes. It's actually correlated very well with repeatability studies, and it's correlated pretty well, actually, with our biometry data. Usually, the Lenstar and the i-Optics Cassini will match up nicely, and then the Galilei will provide a third measurement for us. As far as the axis goes, they usually all pretty much match between those three.

When they don't match, I look at the picture. I look at the anterior, I look at the total corneal astigmatism, and I look at the Placido image on the Galilei. I find more and more that it's this subclinical ABMD, subclinical dry eye that really makes the axis a big issue. I have no problems calling the patient and remeasuring—usually, the patient is in the office with us—either a different device or just taking a look at the patient. Sometimes you're seeing them the first time and seeing why their axis is not ...

I used to go see all these patients preoperatively that evening before surgery, go through all my IOL calculations, but I've actually moved over to addressing them right when I see the patient before I go in there. It helps me decide, “Is this all I'm going to do for this patient or not?” It's been kind of a change. Maybe that will change the busier I get, and I won't be able to do that, but for now, I think I have the luxury of thinking right before I go in to talk to the patient.

Gary: I think that's really good advice. You've brought up something a couple of times that's kind of near and dear to my heart, and that has to do with ocular surface disease and especially anterior basement membrane dystrophy. I've been working on a study and will continue to work on and refine this, but I've found that anterior basement membrane dystrophy is just an incredibly common dystrophy and may be actually more in the realm of ocular surface disease and may be more of a degeneration than a dystrophy. I've been actually doing some keratectomies on patients who have ABMD. I've just had some incredible surprises to the tune that you wouldn't even believe. It's amazing how much irregularity those subtle little maps and dots and fingerprints can cause, especially when they're located in the central 3 to 5 mm. Do you do that at all? Do you do keratectomies on patients?

Sumitra: Absolutely.

Gary: What are your criteria when you find ABMD? When would you say, "This ABMD is bad enough to treat?" Do you have any criteria or thoughts on that that you'd like to share?

Sumitra: Well, I train the residents too, and I teach them, they're all afraid to do this, to lift the lid. A lot of times, you'll see superior ABMD, and then when they stain, they need to look for that reverse staining pattern. Oftentimes, you'll see that, and the map dots will suddenly come out at you. Those two things are very important. If I see actual clinical, I can just see it with a slit lamp, I have a very low threshold to counsel the patient. I let them decide sometimes.

If they have mild ABMD, the lens calculations look very good, the standard deviations weren't too far off in the biometry, I'm pretty confident about my lens calculations, I'll aim them to be a little myopic. If they just want to proceed with cataract surgery alone, because some of our patients are not as concerned with the refractive outcome, and doing epithelial debridement does delay their cataract surgery. If they come in with a very mature cataract when they're 20/80 or 20/200, I kind of counsel them, "Look, you're lens calculations may not be that accurate. Let's aim for myopia, and then afterwards, we may be able to do epithelial debridement or PTK.” Otherwise, it would be much preferable to do the epithelial debridement before.

I have a lot of second opinions on patients who ended up hyperopic after their cataract surgery. When I look at them clinically, they had very apparent ABMD. If they had just caught that ahead of time, they could have counseled the patient at the very least, but maybe even treated the patient ahead of time. Then you have to be really careful about doing epithelial debridement or even PTK on a patient who's already had cataract surgery with a hyperopic outcome. You're going to make them more hyperopic, more uncomfortable, more blurry.

I counsel the patient about it, and I let them decide. I take care of veteran patients who aren't that concerned necessarily all the time with it. I take care of some elderly patients who have very dense cataracts and are interested in going back to driving as quick as possible. For those patients, if they want to proceed and they just have mild to moderate ABMD, that's fine. If they have significant ABMD, though, I tell them, "Listen, we really need to go forward with epithelial debridement first."

Gary: I totally agree with you. We have to always keep our patient at the center, and we can make recommendations, but we do need to let them continue to drive the process in that regard.

Another thing that is obviously a hot topic, especially when we talk about Baylor, is really the Baylor toric nomogram. Talk to me a little bit about maybe the thought process behind that and what you all do when you implement the Baylor toric nomogram and the trends that you're seeing with that.

Sumitra: Much credit needs to be done to Dr. Koch, Dr. Weikert, and Dr. Wang who really went into the work to do the Baylor nomogram. Dr. Koch was noticing that he was having these surprises with some of his patients after a toric placement. Looking back, they had the Ziemer Galilei data, which showed the posterior cornea. They found over time that, although anterior corneal axis changed over time from with the rule to against the rule, the posterior cornea essentially stayed the same. Eighty-five to 90% of patients actually have with-the-rule posterior corneal astigmatism. You have to take a step back and think about it mathematically. The posterior cornea is negative, so really it's the opposite of what the anterior cornea is. If you have a with-the-rule anterior cornea and a with-the-rule posterior, you're actually subtracting out the posterior. That's why some of these patients were ending up with a flipped axis over time.

There's really two things about it that you have to think about. One is the posterior cornea. It helps to measure the posterior cornea because not all patients are actually with the rule. Some patients are against the rule, in which case the Baylor nomogram is not going to work for you, because it's actually the opposite of what most patients are. That's important, especially if you've got a device that measures the posterior cornea. You have to think that not everybody has a device though, and some of these devices are very expensive. Looking at the Baylor nomogram, it does work for most patients if you just have anterior corneal measurements, and it's able to basically help you from flipping the axis on with-the-rule patients and help you from under-treating patients who have against the rule.

We've got some great devices out, too, that are measuring the posterior cornea. We're not sure what to do with that number yet. I think more work needs to be done into it, and more work needs to be done as far as repeatability and predictability of those posterior corneal measurements and the total corneal astigmatism. It sounds like it's going to be a great avenue as far as measuring the posterior cornea.

In addition, the ORA is kind of nice, because it can actually measure both for you and give you maybe a tiebreaker if you're looking between two different torics if you have that available. You can actually have a bad outcome in two different ways if you don't put the right toric in. If you don't take account the posterior cornea like we talked about, then you'll end up having some very odd results afterwards.

In addition, a patient who's young, is with the rule, then over time, they become against the rule. We don't know why that is. There are some theories that maybe it's stromal degradation because of their aging. Maybe it's epithelial remodeling because of the lid, because of exposure, because of tear film. If you take a young person, leave them with some residual with-the-rule anterior, it'll actually help them over time because they'll become more against the rule over time. You have to keep that in mind, too. Not only is the posterior cornea important, but also the changes in the anterior cornea are really important, too, especially considering the age of the patient.

Gary: I think that's a great point. We think about the cornea, and we think about numbers and static measurements, but this is a living tissue that does have the ability to change over time. It's sometimes frustrating that we want it to be one thing, and it's really another. We want rules, but the cornea doesn't know that it needs to have rules and doesn't follow our rules. Nevertheless, we really do appreciate the fact that the doctors like yourself and the ones that you work with have spent so much time and dedication and effort to making our profession better, especially with reduction and elimination of astigmatism.

Sumitra, I just want to say thank you so much for taking some time to come in today to talk to us about your expertise. We clearly want to follow your progress throughout your career at Baylor, and if you ever want to come back on when we have other topics, feel free. Thank you so much.

Sumitra: Thanks, Gary. This has been great.

Gary: Excellent, excellent. This has been Ophthalmology off the Grid with Dr. Gary Wörtz. Until next time.

Dr. Khandelwal gave us some us some great pearls for astigmatism management before surgery, but I wanted to get some more insights into what to do when there are issues after surgery. To explore this, I sat down with Dr. John Berdahl to hear his take and to learn more about astigmatismfix.com, a tool that helps surgeons fix residual astigmatism caused by common measurement deviations.

This is Dr. Gary Wörtz with Ophthalmology off the Grid, and today I have with me Dr. John Berdahl. John and I go back quite a ways to a time that he came to Lexington one snowy winter and gave a talk on the LenSx laser. That actually piqued my curiosity on being an early adapter to the femto platforms. I was really impressed with the talk he gave that night. We became friends after that and just have had a lot of time since then to talk shop and compare notes and compare techniques. John, with that being said, I just want to say thank you for coming on the program today. Looking forward to hearing some insights that you might have to share with us about astigmatism today.

John: I'm excited, Gary. I remember that night well, too, because it was way warmer and snowy in Kentucky than it was here in South Dakota.

Gary: Yeah, exactly, exactly. John, one thing that I think boggles physicians and especially cataract surgeons has to do with picking toric lenses, taking measurements, trying to figure out the right algorithm and perhaps the right technology, the right combination of tools to use to diagnose astigmatism accurately preoperatively, and then what happens after surgery when maybe we didn't hit the mark. Either the lens has rotated, the patient has residual astigmatism and we can't quite figure out why, or the lens was the wrong power.

There's a multitude of issues that can interplay, and it really is a topic that I think is coming to the forefront of attention because it seems like toric lenses are really that low-hanging fruit for surgeons to enter the premium market. It's something that patients really understand the need for. It's very easy to communicate, much more so than a multifocal lens, for example. With patients understanding and wanting their astigmatism corrected and surgeons wanting to do that, it provides a lot of challenges to overcome. Just real quickly, I'd love to know just at a high level, what do you do for patients who want to have their astigmatism corrected, and what kind of tools are you using preoperatively to diagnose their astigmatism.

John: Yeah. When a person has astigmatism, we offer them a couple of different options. If their astigmatism is between 0.50 D and 1.50 D, we're usually creating femto-assisted AKs. If it's greater than 1.50 D, then probably a toric lens. Now I'll fudge that a little bit and be a little quicker to use a toric lens in against-the-rule astigmatism at lower levels and maybe take AKs a little bit higher than 1.50 D but not much if the astigmatism is with the rule.

Gary: Sure.

John: As far as the preoperative testing, I want at least a couple of confirmatory sources of Ks. We use the Nidek OPD-Scan, and I really like that. We also have used iTrace, and we like that a lot too, in addition to the Ks that we get from our Lenstar. Then I pay attention to the axis of astigmatism on the manifest refraction and just if it's not lining up with where the Ks are at, then I assume that they've got some posterior corneal curvature or some lenticular astigmatism. You can't really know for sure which one it is.

I also fret about that less than I used to because, ultimately, I'm relying very heavily on ORA intraoperatively. Even though preoperatively is where the decision is made, intraoperatively is where we try and nail it.

Gary: Sure. I think that's a great set of tools you have to work with. We've really tried to streamline things in our practice. We have the Nidek OPD-Scan III as well. We also have a Lenstar, and it's really amazing how well they correlate. When they don't, there's usually a reason. Usually, they have some ocular surface disease problems such as evaporative dry eye, meibomian gland dysfunction, or there's just something weird going on with the cornea like, for example, they have ectasia, or they have EBMD, or Salzmann's nodule causing some irregularity.

I agree with you. I feel really comfortable when things when things line up, but I know some people will use eight different topographers or corneal analyzers. At some point, you have to declare what you're going to use and what you're going to trust. I find that you've got to find one or two, probably more than one, but you need to find two or three, but I don't think more than three, devices to use routinely on your patients to find out what is really going on with their cornea. I think beyond that, you start chasing your tail, and you don't know what to trust. Do you agree with that?

John: Yeah, I do agree with that. More information isn't always better. Some of these machines aren't designed to give you the same information. For example, let's say, Verion gives you a little bit different Ks than a Lenstar gives you, because it's measuring different points. It makes it hard to develop an intuition about what you're going to trust. It took me a while before I decided that what I'm really going to trust is aberrometry. That's going to be my final common pathway, but the other things are going to help me out.

I wanted to back up just a second because I think that it's always worth talking about correcting astigmatism in terms of what our goal is. The patient doesn't really care about astigmatism. They care about how they're going to use their eyes after surgery. I really think about it in terms of, "Do you want to wear glasses? Are you hoping not to have to wear glasses after cataract surgery for distance or not having to wear them much at all?" Then take that approach first with the patient: “How do you want to use your eyes after surgery?”

Early in your monologue at the beginning, you talked about how the toric lens is the low-hanging fruit. I think that that's mostly accurate, but we've all heard, "Well, at least do torics," right? “You can't really screw those up. They're the low-hanging fruit. They're easy.” I think that we've learned, especially with competitive IOLs on the market now, that you don't always nail it with a toric lens. I think it's a big reason why presbyopia treatments have failed, because we are not going to be able to treat presbyopia until we can consistently treat astigmatism well. Frankly, I don't think that we're there yet with consistently treating astigmatism well enough. We do pretty good but not great.

Gary: I think that's a great point. Something along those same lines, when I talk to patients about correcting astigmatism, I never use that term. I also talk about reducing their astigmatism because the reality is, most patients, if you refracted them, they could pick up a 0.25 or 0.50 or maybe even more. The reality is, if you're reducing their astigmatism, these patients notice a qualitative improvement in how they see versus comparing their postop vision to their preop vision.

I think you're exactly right. It's all about goals. It's about discussing what the patient wants, and the reality is I think that when I say low-hanging fruit, I think that patients are more forgiving of leaving a little residual astigmatism even though that's not our goal. Our goal is perfection, but typically patients are a little bit easier to please in the toric category because they're seeing such a tremendous difference based on what they've been used to.

John: I think that that's right. And you're only fixing one problem, whereas with presbyopia, you better fix astigmatism and presbyopia. With astigmatism, you only need to reduce the astigmatism.

Gary: Exactly. I totally agree.

Now, John, one other tool that you have created that really goes beyond just the normal average physician's understanding and desire to correct and understand toric IOLs specifically is your website, astigmatismfix.com. Can you talk a little bit about that tool for those out there who may have not used that or haven't heard of it and discuss maybe some of the things that you've noticed as you've maybe been able to look at the traffic patterns on there in terms of what things are needing to be corrected and why.

John: Yeah. Astigmatismfix.com is a free website that we created that helps surgeons that after they've implanted a toric lens, and if they have an unsatisfactory residual astigmatism, they can go in and type in a couple of straightforward numbers—basically your manifest refraction, which toric lens you put in the eye and where it's at now—and it will calculate for you where to rotate it to to minimize the astigmatism.

How it came about is I was doing my fellowship with Dick Lindstrom, David Hardten, Tom Samuelson, Liz Davis, Sherman Reeves, and the crew at Minnesota Eye Consultants. Hardten says to me, "Hey, you were a math teacher. Figure this problem out. I got this patient. I put a T6 lens in him, and they've got residual astigmatism. I don't know exactly what I should do." We put together a computer program to calculate that. Every once in a while on the ASCRS list serve or whatever, somebody would mention this problem, and I'd send them a spreadsheet. I found myself sending this spreadsheet out a few times a week. Ultimately, I said I'm going to save myself time and make a website and let everybody go to it themselves and save some electrons on email.

I was astounded by how many people used it. We get just less than 1,000 entries a month. Now, not all of those are unique—probably about half or so are unique entries a month. We're probably getting 400 to 500 unique entries a month. That really shocked me because this problem is much bigger than we thought that it was.

Because we've got this huge database, we're able to look at it and say, "What does this mean? What can we learn from this? Why are people having residual astigmatism?" There's a couple of things that we learned from analyzing over 30,000 entries. Number one is that when residual astigmatism occurs, about 70% of the time it's because the preoperative measurements were not indicative of what would be the ideal final location of the IOL. I'm going to say that one more time. The preoperative measurements weren't indicative of where the ideal position of the IOL should be at the end.

Then what we also found was that when there's residual astigmatism, about 70% of the time the IOL is rotated more than 5°. Fifty percent of the time, think of a Venn diagram, it's an overlap of those two. It's a combination of those two and compounding errors that gets you to a place where they have 0.75 or more of astigmatism.

Now that's not to say that the preop measurements were wrong. It could be that there was a posterior corneal curvature that's surprising. Doug Koch and their team has taught us so much about that. One of the things that I think is ... just to reiterate for everybody, Doug Koch and Liz and team would say, and Mitch Weikert and everybody, would say that on the posterior cornea, there's about 0.30 or so diopters of against-the-rule astigmatism. In most cases, you should correct for that and over-correct against-the-rule astigmatism and under-correct with-the-rule astigmatism. That goes along with the lore that we've had for years. Leave people with a little bit of with-the-rule astigmatism. I believe that's not because there's some benefit to it optically. I believe that it was a fudge factor that we just evolved into because we didn't want to over-correct them.

Anyway, but that's an average measurement. When you look at the data, about 17% of people in Doug Koch's study showed that they've got with-the-rule astigmatism on their posterior cornea. If you just give them an average, four out of five times, you're going to improve people, but one out of five times, you're going to make them worse than if you used no nomogram at all. Just like we don't give everybody a 22.00-D IOL anymore and we don't give everybody a size 9 shoe, I'll take a measurement over an estimation any time I can get it. That's why I think things that are trying to measure the posterior cornea or things like intraoperative aberrometry are so helpful. That's one point.

The second point, and possibly even more important, is surgically induced astigmatism. I like having this conversation with folks and asking, "What's your surgically-induced astigmatism?" Everybody like me says that it's 0.30 D of flattening in the axis of my incision. That's right, and that's what I get, too, but when I looked at my histogram on my standard deviation, man, it is all over the place. I'm like, "God, am I worse than everybody else's?" Turns out, I'm not. I'm just like everybody else's. I went in to the literature, and everybody's got a flattening of about 0.30, 0.40 D of flattening in the axis of the astigmatism, but the standard deviation is about 0.70 D. One standard deviation includes 68% of the data. That means 32% of the data is outside +/- 0.70 D from 0.30 D. A third of the time, you're inducing over 1.00 D of astigmatism. The corneal biomechanics and the wound healing and all that kind of stuff I think plays a much bigger role than any of us would like to admit.

Gary: John, I have to stop you there and totally agree and tell you that you've made me feel a lot better. I just went through this calculation about a month ago, and I found the exact same thing. I was about 0.30 D, 0.40 D in the axis of my incision, but there were a couple cases that were beyond 1.00 D. I thought, "What happened? Am I just a bad surgeon? What's going on?" You made me feel a lot better that's it's not just me. These corneas, they're living tissue that will react variably to incisions. I think we sometimes overlook that and think about the cornea as simply something that gets us access to the anterior segment.

John: I think that's exactly right. There's a couple of things. One, there's nothing more humbling than looking carefully at your own outcomes. Number two is when I turn, my human nature is, "God, if I'm this bad, I really hope there's other people that are this bad and struggling with it too," so I can commiserate with you, Gary. At least we have each other in our surgically induced astigmatism ...

Gary: Club.

John: With delinquencies.

Gary: Yes. Got it.

John, for people who are out there, if you had a couple pearls to give them, because it sounds like the biggest problem is really garbage in, garbage out. You said 70% of the people who go on your website, astigmatismfix.com, to try to figure out what's going on with their postop outcomes, it really has to do with data that is not correct. What kind of pearls would you give them, either for preop data or maybe even surgically? Any pearls you might have for preventing rotation or maybe patients that you might want to do something a little bit differently if they're perhaps a high myope with a large bag?

John: Sure. My biggest first pearl is have a plan to get them into the end zone. There's going to be a percentage of people that you either have a surprising surgically induced astigmatism, or it rotated a little bit, or your preop measurements weren't right. If you don't have a willingness to either do an exchange or rotation or laser vision correction or access to somebody who does, you're setting yourself up for failure on patients once in a while. Think about the end game in mind and how you're going to get people happy. That's, I think, the most important thing because we can almost always get them to a place where they're happy if we're willing to take step number two and three if we need to, not just flop a toric lens in there. That's number one.

Number two is that high astigmatism is a different animal than low astigmatism. If you've got 1.00 D of astigmatism on the cornea, and you put in a 1.00-D toric lens, and you're off by 10°, you lose 30% of the effectivity. Whatever, they've got 0.30 D of astigmatism leftover, everybody is happy. You do that same thing with a T9 that has 4.11 D of astigmatism, and you've got a third of that left, which is 1.50 D of astigmatism, everybody is unhappy. That's why I think that lower astigmatism is a much different animal than a high astigmatism.

The next pearl I have is get your alignment right. Ten degrees is not that much in the operating room. You've got to get alignment right.

Number four is, I think, really important. Think about some sort of aberrometry approach because it's measuring things that we can't measure otherwise. It measures the posterior corneal curvature, which other devices can do, but it also measures surgically induced astigmatism, which we've already talked about the variability there. At least you're measuring that after the incision has been created.

Gary: Yeah, I agree with you, John. I think that all those things are really, really important to think about. All the pearls you've provided us, it's really just a treasure trove for either folks just starting out on this journey of correcting astigmatism or perhaps folks who have been doing it for a long time and are still banging their head against the wall when things don't go right, which it does happen to all of us.

With that being said, John, I just want to thank you for your time. Thank you for your insights. Hopefully, this will benefit a lot of folks who are going to be listening in. Thanks again.

John: Gary, it was really fun. Thanks for having me, and I appreciate you a lot, man.

Gary: Okay, this is Ophthalmology off the Grid with Dr. Gary Wörtz. Thanks.

Thanks for listening to this episode of Ophthalmology off the Grid. To hear more, download other episodes on eyetube.net. Until next time.

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