 I'm just going to kind of start about where we left off last time. We were talking about higher order aberrations. And I had mentioned to you guys that probably the most important thing that you need to know about for higher order aberrations is spherical aberration, just because that's one that is most clinically significant. Coma you'll kind of hear about. It's also something that you should kind of know a little bit about, at least kind of superficially. But spherical aberration is really important. I don't know if this pointer works or not. Do you want to go with that? Yeah, it's OK. I mean, I don't really need it. Yes, cool. All right. Yeah, so I mean, again, I'm not trying to just like totally teach to the test, but there's so much to remember when you're a resident. And this is something that you kind of just, if you can kind of remember that diagram, then in understand spherical aberration, that's huge. Because so much in IOL surgery and refractive surgery now is basically tries to compensate for that. And so it's just kind of important to understand. Coma you can kind of think of as asymmetric as stigmatism as kind of a good way to think of that, which one of these advances here are just. We might be on the dominant end of the two. I don't think so. It doesn't matter. I'm standing here anyway. I don't need to walk around. So there's two different ways of based. I mean, there are more than two. And I'm not a math whiz, but you'll see higher order aberrations described as Xerniky polynomials and also Fourier analysis, which I mean, there's a reason why I didn't become a mathematician. I don't really give a darn, but you'll see those things. It is important to understand wavefront both. And we use two terms. We use the term guided and optimized. And this is an example of the VizX, which is probably the second most common laser worldwide used for refractive surgery. And it's called a wave scan analysis. So wavefront is not using the refraction as the primary guiding kind of programming, I guess, you would say, method for the amount of correction. It's using an optical computerized data set, which is collected by a machine called an aberrometer, which I think we might have showed that last time. But the aberrometer is just a scanner. It just shines low energy. It's kind of infrared spectrum, collimated light into the ion that it's reflected out and collected on a sensor. And there are a couple different ways of aberrometry. The most common is Hartman-Shack, which is what I just described for you. We don't really need to talk a lot about laser biophysics. And this slide has too much on it. I apologize for that. But the important thing to know is that eczema laser is UV light. And the femto-second laser is more in the infrared spectrum. So femto, obviously, very short or high frequency, longer wavelength. And I think, again, it doesn't really matter that much. You might see something about how eczema lasers work. And usually there are, I mean, I've definitely seen questions on OCAPs and things like that, talking about toxic gas from the eczema laser system. So know that fluorine is used for eczema lasers. This one here, I don't even know why it's under laser. I don't know that I. It's in the book. And they talk about this conductive keratoplasty. And thermo keratoplasty is not done. But it was a technique that really didn't work very well. And it was using a yaggles or trying to shrink the cauldron tissue and create a little bit of a hyperopic or prolet hornia. But I guess for historical purposes, it's in there. You can know about that. One of the great things about eczema lasers, they're very precise. And they don't create a lot of heat or collateral damage. And that's why they're so good at sculpting corneas. And this is just a little picture. It's an overused picture. But showing a human hair that's been etched. And anybody who's ever burned hair knows that if it's thermal, it's going to burn or melt or whatever. So this is important and really basic. But just know that the size of the, you'll hear about Munnerland's formulae. And it's actually important clinically. And one of those really super easy formulae that you can remember might show up on a test. But the depth of ablation for it to have a certain effect is going to depend on the optical zone. So you can get more bang for your buck from a small optical zone. But the quality of the vision won't be as good. So generally, when you're doing an eczema laser ablation, and this applies to myopic treatment, you want a bigger optical zone because you want to treat the space that the light goes through, the pupillary aperture. And for most lasers, it works out to about 15 microns per diopter. So again, that's just something that could show up in a test fashion if they said, OK, this person's a minus 9 in their corneas, 500 microns. Or should they have LASIK and what formula would you use? And you'd say, well, I don't know what's going on. But really basic stuff, and that's one of the reasons I like refractive surgery because it's really basic. I was almost an orthopedic surgeon. So I feel like corneas, like the orthopedics of ophthalmology, like framing and hammering. And it's cool. Maybe plastics, too. So it's really important that eye exam is the probably the most important thing for vision correction surgery because it's really the basic things that's going to get you into trouble. And it's elective surgery. So staying out of trouble is what it's all about, really. Because it's actually really, really effective, great surgery from a technical standpoint, from the technology. It's just super, super high yield. But you can be tripped up by the clinical characteristics of the patient. And all of these things are important, but I would really emphasize dry eye is super, super important for LASIK. And I'll talk more about that either today, depending on how much time we have or in the next lecture. We kind of have danced around this concept of corneal thickness, but I haven't really fully explained it to you. But again, we'll talk about that more. But just know that, obviously, the shape and thickness of the cornea is really important if you're going to alter that and kind of violate it structurally. Surprisingly, endothelial health is really not a great big factor in vision correction surgery. But it's something you need to be aware of. And this is obvious. And again, you'll see that on kind of test type situations. We'll look at some. We didn't really spend a ton of time on topography last time. We just talked about really basic concepts. But I think any of you would understand or recognize that this isn't something that you see every day. And one good thing about modern cataract surgery is that pretty much every patient is getting a topography now. So when you guys get into cataract surgery, you're just going to be looking at all these topographies. And so which in clinic, you don't always do that because you don't need to do any of that. Hopefully with the new cornea rotation, you're exposed to that a little bit more in your second year. But it's kind of the way the residency is set up. You don't get a lot of exposure to this until you're third year, usually. But with cataract surgery, I think you're going to get more. But you might recognize that this is not a really orthogonal, great-looking topo. Dr. Betz, what else about that topo on the left, would you say, might raise suspicion? What are some other things that you could look at to try to get an idea of whether that's a cornea that you want to do, LASIK or PRK on? I mean the kind of the maximum steep area. Yeah, the maximum K on the CIMK is, anyway, is 47. And if you look at the color scale, maybe even higher. The difference between the low and the high. Right. So there's this IS gradient that you'll see written about. So yeah. And the most important thing is what? The pattern of the astigmatism. So anytime you see boomeranging or oblique kind of stuff, or comma, or I don't have a picture of it, but there's an entity called a D shape that's described. That pattern is the most important thing to recognize for risk. And you may remember these are both Placido images. Placido is a snapshot. It's the concentric rings. It's a snapshot. And that's actually really the best way to recognize that pattern of abnormality. This one, I think we would all recognize as abnormal, and that's sometimes described as a sagging bow tie or a crab claw, commonly associated with what? Pollucid. Pollucid. Yeah, I mean, if you saw it on test, you might say pollucid. But it certainly could just be, you have to look at the patient to know if it's pollucid or just low carotid comets, because you see this all the time in carotid comets. But yeah, technically or kind of classically, I guess it would be. So this is a tomography. And so again, the arrow kind of gives it away. But what we're looking for, and I don't know if this is an older one here, but you may remember I told you guys in the last lecture the best fit. And I think that says S, but I can't really tell. That's not a great picture. But that would be Sphere. But a lot of times, it'll say best fit, toric, elliptical front. But anyway, it's comparing it to a reference surface. And so this is the posterior elevation, or often called posterior float. And that is a really, really sensitive way of picking up kind of a weakness or carotid comets-like pattern in a cornea. And you can look at the anterior topography, and it can look completely normal. And the posterior topography. And as you can see, this anterior elevation, that's actually a really normal pattern. This is a representation of a kind of a, I don't know if it's axial or tangential, but it's basically the topo recreation from Pentakam. And then this is the posterior surface of the cornea compared to best fit reference curved sphere. And so when you see red, and again, I'm spending a lot of time on this, because I think it's really important to understand how it works, and it's really simple, but if you don't get it, it's completely worthless to you. So just think of a curved plane. If it's above the plane, it's gonna be red. So I always think of the patient laying on their back. It's easier for me to think like a topo map, like a mountain. But if it's red, it's above that reference plane. So that means our posterior cornea is bowing in. There's aqueous behind that red bump, right? And if it's blue or cool colors, it's below. So if you had a kind of a convex out posterior cornea, which you almost never would see, unless you have cornea with a demon or something like that or just amazed attachment, it would look the opposite. But you can see on the anterior surface, there's really no bowing. So there's a dent in the back of the cornea. When we look at the regular maps, we look at the little numbers, the little micron numbers will be superimposed. And by looking at the actual absolute values, you can tell a lot by, you know, the degree is important, because most corneas are not perfectly symmetrical. Yes? Can you say for the posterior cloud that red is bowed? It's bowed towards the air. So think of it as a dent in the back of the cornea. And again, because it's kind of a reference to, you know, maps, you know, top of the, I like to put the patient on their back. If I'm operating on them, it's a mountain. That's a little cave in the back of the mountain or something like that. You know, it's basically bulging up. And if you just think about keratoconus, you know, I mean, you can put them all together. It'll be consistent. Keratoconus is a red bulge on the eye. This is just a red bulge on the back surface of the cornea. So we're gonna talk a little bit more about the other types of vision correction surgery. And RK type procedures or incisional procedures have been around for a long, long time. I think people recognized maybe from trauma or other surgeries or early cataract surgery that making an incision could alter the shape. There was this guy in Japan who recognized this and he was taking this thing called a Sato knife. It was like a sickle sticking it from an incision at the limbus inside the eye and making internal cuts. As you can imagine, that didn't work very well because the corneas were very ademinous, but it did fly on the cornea. Got rid of some near sight of this. And then Fyodorov was, I don't know if he invented RK, but he was definitely one of the pioneers of Russia. He was actually a contemporary of some of my teachers. And incisional surgery was kind of crazy when you really think about it, but it's kind of, I think, a good historical commentary on how desperate people are to not wear glasses. And I think it gives us some context on some of the crazy things that might be available nowadays. Presbyopia surgery is another area where people hate reading glasses, I hate reading glasses, but so people do some crazy things to try to be able to see. And sometimes there's a lot of long-term issues that can come up. And RK is certainly a great example that you should know about the PERC study. Just basically know that it was a well-designed, longitudinal study that showed that RK was not stable. People had hyper-opic drifts. I'm sure probably all of you have seen a patient with a plus two or a plus three refraction. They're 50 or 60 and they had RK. And that's really the main take home of the PERC study. The way that RK works is it actually creates a flat center. So unlike myopic laser, which scoops out a little bit of tissue and alters the anterior curvature, this alters both anterior and posterior curvature. And that's one of the reasons it makes counteract surgery a little bit harder to calculate IOL power with RK compared to... LASIK doesn't really change the anterior chamber depth much, but RK certainly can, especially in extreme cases, because it's really flattening and oriented. And also the extreme flattening that you get with RK really kind of distorts that higher order aberration kind of mix that we talked about before. You can imagine a tabletop, it's kind of really gonna give you a lot of aberrations, especially with all these cuts. And if you may have a small optical zone, you're gonna get a lot of scattered. The concept of an optical zone is kind of an important one to understand refractive surgery. So in general, and it doesn't matter what you apply it to. So before I was talking about Munnerland's formula, if you have a really small optical zone, LASIK ablation, the smaller you have, the more powerful it is, you're gonna have more side effects from it. But if you had a 4.5 millimeter optical zone, you wouldn't have to go nearly as deep to treat five diopters in myopia as if you had a 6.5. So you can just extend that thinking to incisions. The further in a radial keratotomy incision goes, the more flattening it's gonna create, the more effect you'll have on myopia. The same thing applies to arcuate or transverse incisions. The closer they are to the center of the optical zone, the more effect they're gonna have. Length and number are also important, although surprisingly not as important as optical zone. Age of patient is very important in incisional surgery. And this comes into play again in modern cataract surgery because we do relaxing incisions both by hand and with the femtosecond laser. And I'll talk more about that in a sec. So we use knives to do RK. Originally they used broken razor blades, believe it or not, and just take a razor blade and break it and use a little piece. But diamond blades have really become a standard of care. Generally they're guarded blades and again we use these in the operating room for cataract surgery. So those of you who are to that stage would recognize these. They can be set at a particular depth. Ultrasonic Pachymetry intraoperatively was always the gold standard for radial keratotomy. And perforations were not uncommon, but the idea is to get as deep as you can without perforating. And perforation is not really a big problem. Most of these blades were designed with a very pointy sharp tip and so if you got a perforation you would immediately know it would self-seal and not a big deal, but you have to really pay attention. Then talk about nerve racking surgery. You know, topical anesthesia, no fixation of the eye. That's a bit kind of crazy, but it worked pretty well. But lots of other complications as well. And again I would say most of you have already seen some bad trauma outcomes from radial keratotomy. Incisions are kind of like cornea transplant incisions, only worse because they haven't been sutured and so they split open pretty easy when you get hit in the eye. And you know, it's kind of a fairly common thing to see loss of iris and lens through RK ruptures because they tend to open up pretty big. But all of the other things that are listed, not associated with this picture or problems with radial keratotomy as well, and especially with smaller optical zones. So radial keratotomy could, was used to treat up to, you know, maybe even nine, 10, or more diapters of my opiate. Sorry, there are always problems under it. Not the easiest ruptured globes to fix either. Oh, actually this is a good teaching moment. So what's wrong with that picture? We'll pick on Eileen. She's in a cornea right now. Dr. Betts knows, because he supervises trauma. Although I don't know if he's awake yet. But that's the problem. That's the problem with that picture. Bury your knots. Bury your knots, guys. Bury your knots. There's nothing more annoying than being the attending and taking over the ruptured globe, which happens all the time because, you know, you guys can't always follow him. And then there's all these knots and all these are on the surface and they're in my eye hurts. I'm like, yeah, no kidding. And then you try to bury him in the clinic and you break it in leeks and bury your knots. So again, one other really, really important thing about RK is diurnal fluctuation. And mainly because it relates to modern cataract surgery. Almost every week, I would say at least twice a month we have arcane patients on our cataract list and they're difficult to calculate. There's an interesting psychology of refractive surgery and probably you see it in cosmetic surgery as well. But the kind of people who sought this surgery 20, 30 years ago are the kind of people that are gonna be, as my former partner, Dr. Moshe Hart would say, PETA patients pain in me because they want perfection and you're like, you have it totally screwed up by, I can't even get you anywhere close to perfect but that's what they want and so, you know, we try. But so it's really important to understand that almost all RK patients flatten out after sleeping so their corneas tend to be more flat when they wake up in the morning and they get more myopic through the day. It probably just has to do with the actual, you know, kind of an ectasia type thing through the day and some people think, well, the lid's closed and that's the end gets edematous or whatever but I think it's actually more mechanical. I think it's actually their entire chamber gets a little bit weaker. We already talked about the perfect study. So the clinical pearl there is that if you have somebody with RK, get biometry in the morning and in the afternoon if you're gonna do cataract surgery because it may help you. I think it does help. One interesting historical thing about RK, you guys may know the story, probably Beck Weathers. He was a pathologist. That movie, Everest, has anybody seen that movie? The climbing movie, it talks about this expedition. He's like a real jerk pathologist, I guess, from Texas but he had RK and it was kind of the reason that he almost died on Everest and got, you know, severe frostbite but high altitude and really low atmospheric pressure it's kind of like the diurnal fluctuation thing would allow the internal ocular pressure to push the eye and change the shape and they actually become, and again I don't know exactly what's happening but they become more hyper-opic and high altitude as opposed to myopic but anyway, this is a problem for climbers. Not really much of an issue for Lace, unfortunately. So if you have an over-corrected RK, which is typically the case because you almost never see under-correction, you can do LASIK or PRK to try to correct that but you have to remember those flaps are kind of like pieces of pie or pizza and they can kind of come apart maybe. So our first preference is probably not to do LASIK. We usually do PRK or many of these patients have cataracts and so you can adjust their power by replacing their lens. But it's very important not to promise too much because they're challenging. One thing I don't think is in my lecture but it's also useful is suturing the incisions is sometimes helpful and I think the book has actually mentioned that. I don't have the latest version of the book so I apologize but there's, you can actually make a kind of a sir-clawed suture it's called a lasso suture and it actually works but after a few years the suture may break and but just know that suturing, again, that could be something that would show up on a test possibly and say okay, how do you correct over-corrected RK? Why you can do cataracts or do you can be licensed for PRK and suture their incisions? Generally we target minus one. Can anybody think of the logic of that? Nico, I'll pick on you. You don't have to know anything about cataract surgery. Why would we pick minus one as our target for a somewhat unpredictable surgery, cataract surgery after RK? This applies a little bit to LASIK but mostly RK. I think LASIK is a little bit more precise. Yeah, any ideas? We usually like overshoot and that's why you... Yeah, you have a variable, you don't really know. I mean it's just like, it's kind of a, it's a probability thing. So if you know that you're going to not be precise, shoot for a target that the patient's gonna be happy with. So if you shoot for minus one, let's say you're a die after off in the plus direction on the number line, then they're plano, they're happy, right? They're a die after off and then minus out of the number line, they're minus two, they can read without glasses. So if they end up minus one, they're 20, 30, they can see their computer. So it's just to kind of common sense, really. And there's one other reason, and can anybody think of another reason why you might shoot for minus one in the RK patient? I still shouldn't do that. Yeah, yeah, I mean it's not like cataract surgery is gonna stop their hyper-opic progression. So they might actually progress more hyper-opically. And then there's one more really important feature on cataract surgery after RK that, again, I'm pretty sure it's in the book, but I don't know if I put it in here. I didn't actually put it in here, but, and I'll just tell you, because time is limited, but it's really, really important to understand that cataract surgery will loosen up those incisions. And the cornea is sometimes kind of trampoline and they're just really loosey-goosey. And your post-op results may be really sketchy, initially, so don't overreact in this light. So okay, we're just gonna let this cornea kind of tighten up and settle. And so generally it's a good idea not to do an IOL exchange or even think about that for at least a month after RK surgery, or cataract surgery after RK. There are lots of online calculators. And we're really fortunate here to have Todd and others who, I mean, it's a real science. And if you get these patients, they'll help you figure out what lens to pull for Dr. Prandtl's patient. So you can do cornea transplants for severe RK connotation. So incisional correction of astigmatism is super, super important. Again, as much for refractive or cataract surgery, cataract surgery's basically become a refractive procedure nowadays for most patients. And we talked just a little tiny bit about coupling, I think, last time, but we're gonna spend a little bit more time on that because that's a really, really important topic. So coupling just means that you can kind of get a free pass on astigmatism treatment if you do it right. So you don't need to worry about their astigmatism at all when you're calculating their IOL power if you're doing an arcuate incision because it's gonna flatten equally 90 degrees away or steep in 90 degrees away from where it flattens. So the overall corneal power will not change. It may not be super intuitive. You could actually do it if you had a, you know, a corneal-like model in the lab. You could convince yourself of that. But just know that the incision, this is an important concept. I don't have a great visual of this. I bet we could find one online, but I didn't have time to look for one. But you're almost like you're adding tissue when you make an incision. You're making a little microscopic gate. And what does that do? Well, we know if we make a cut, where do we make it? Where do we make it? What axis? Do we make it on the flat axis or the steep axis? The steep axis? The steep axis, right. So, and remember that a cornea, let's talk about with the rule of stigmatism. So with the rule of stigmatism, what does a cornea look like? Let's use a football season as an example. Is it a football standing on the tee or is it laying on its side? It's actually laying on its side. So think about steepness. And if you just, again, think about the mountain. It's falling away faster, superly and impurely. So it's like a football on its side. So if you make an incision, it's like adding leather to that football in the vertical gradient, because you're creating a little space. The leather of that football is coming forward a little bit. But in order to do that, the points of the football have to sink back a little bit. That's coupling. And it's kind of a one-to-one thing if you maintain this arcuate shape. Now, if you get into straight cuts, which pretty much nobody does anymore, then you get a little flattening of the cornea, cause a little bit of a hyper-opic change. And I wouldn't even commit too much to memory, but because I don't know that that's super important, but I guess it could show up on a test or something. And one way to think about that is this incision or a frown incision would be the other extreme. I think of it as the more frowny it gets, the more it is like an arcane incision. And that's one way to remember. If you start getting kind of a radial component to it, you're gonna flatten the cornea. You just have a parallel arc. It doesn't matter if it's at the limbis or if it's an astigmatic keratotomy, which we might do at a smaller optical zone, it's not gonna change the overall corneal pattern. So that's important to get that concept. Anything else that you guys get out of these lectures just understand topography and tomography. It will help you so much. It'll help you in optics, too, at the time. There's so much of optics and like no caps and stuff in this clinic life. And you're gonna see a lot of questions on this kind of stuff. So I already mentioned, T-cuts aren't really done. That was an arcade thing. We talk a lot about LRI, arcuate keratotomy or astigmatic keratotomy is actually probably a more accurate term. But if it's not right at the limbis, it's basically, I mean, it's all astigmatic keratotomy, but if you move in a little bit, so what we do with femtosecond lasers we're usually at nine millimeters. The limbis is probably, for most patients, closer to 12, maybe in the vertical, we're already at 11, so we're doing AK technically with femtosecond lasers. The way that it works is really just the same as arcade. You just get flattening by the incision and steepening away from the incision. But I like to think of that. And so suture removal is related to these concepts of incisional surgery. So if you had a tight suture, let's use our football analogy again, and it's with the rule of stigmatism, and you know it's tight suturing, it's maybe kind of a little bit more intuitive, it's bunching the tissue, right? It's actually flattening, flattening right where that suture is, and if you see a cornea transplant, you can see the tissue is bunched and flattened, and there's only so much tissue to span that curve. So what happens if it's flattening here, it's steepening adjacent to it, you get like a bump next to it, you take that suture out and the whole thing's gonna kind of shift out. And so, arcute incisions and suture removal basically work the same way. It's like creating a little more tissue, it allows it to span the space more. And I think if you just think about it, you'll get it. Let's see. I, there are all kinds of nomograms for relaxing incisions. I think this is pretty useful actually, and I almost pretty much never do them for anything except for cataract surgery now. But if you want one diopter, two 45-degree arcs is more or less right. If you want two diopters, two 60-degree arcs, if you want three diopters, you're probably not gonna get it unless the patient's 85, but don't ever do more than 75 degrees. And the reason for that is you're never perfectly accurate on your marking, and if you only do 75, well, let me, let me pose a question here. So what's the maximum amount you could get an effect from before you start to shoot yourself in the foot? 90 degrees? Yeah, 90 degrees would make sense, right? But if you're not exactly on axis, it's nice to have a little room to extend that incision. And that's one of the really cool things about relaxing incisions of all kinds, including femto incisions. They're super easy to titrate. You screw up on a relaxing incision or something, you put a suture in it, it will heal. I mean, they're just really, really forgiving. They're kind of like what Dr. Manwells teaches you when you start out doing cataract surgery. It's like, okay, remember him saying, you know, parasyntesis or stab incisions are free. You know, it's like you make as many as you want, and LRIs are pretty dang safe, you know, they're really, really safe. So another thing, again, so much of this applies to cataract surgery. If you become good at relaxing incisions, toric lenses are not as forgiving as relaxing incisions. So if somebody has a little bit of an asymmetric astigmatism or you're not quite sure what to do, sometimes it's better to just do a relaxing incision. Doesn't turn out right. You can suture it, you can add another one, you can, you know, they're really forgiving. Age is really, really important. Depth is important. And one of the reasons that people are not successful with incisions is they don't get them deep enough. You have to get them deep enough, 80 to 90% depth or they're not really going to work. The effect of lid and gravity, you guys should know that there's a natural against the rule shift, meaning, and again, sometimes those terms are confusing. So you just have to think about that football. So with the rule is a football on its side, laying on the turf, the points sideways, and against the rule is the other way. And, you know, whether it's eyelid effect or gravity or whatever, the eyes naturally shift against the rule. Plus, those of you who are a little further along in doing cataract surgery would know that most of the time the internal cornea creates some against the rule or axis 180 cylinder. So when you have an against the rule of stigmatism and whether it's a cataract patient or whether it's, you know, a refractive patient, you're going to be more aggressive on those patients for two reasons. One, the natural tendency is to drift that way with time. So you don't want to have the patient drift and lose the effect. And then the other is there's an internal component usually that you're not measuring on the external surface of the eye. But the converse is true. You don't want to over correct that with the rule of stigmatism because people may drift a little. And then the longer the incision, you start getting in 75 and 90 degree incisions, just like radial keratotomy, they're not super stable over time. So you don't want to be too aggressive with those. You'd rather leave somebody with three quarters of a diameter of a stigmatism with the rule if you can. I think I talked about most of that stuff. Healing is really, really important. The closer it is to the limbo blood vessels, you know, if you draw blood, you're going to lose effect, that's 100% chance. But most of the time we do them where we're going to get some blood because we don't really want to get, you know, we want to get some effect, but not an extreme effect. If we want to get an extreme effect, we're going to put in a toroid cleanse. And it's really important that you don't need to necessarily put that incision on the steep topographic axis symmetrically. So sometimes, and again, I apologize for making this so much about cataract surgery, but this is the practical aspect of refractive surgery. Sometimes it's just your stab incision is going to be where you don't want to make an arc you'll cut just for the ergonomics of cataract surgery. So if I said, well, 245 degrees is what I was thinking about, but that's right where I want to put my stab incision, I may just put a 60 degree limbo relaxing incision in that hand in a place where I'm not going to have a stab incision. And that works really, really well. And you'll learn a lot of that when you work with me. We're not going to spend too much time on this. There are steel blades, disposable steel blades that work pretty well. So in a clinic setting or something like that, you can actually have these around and do a little touch up on your patient if you need to. I saw Doug Mastell last week, he had this really cool. It was almost like a halo frame that you'd put on a spinal patient or something that would kind of put it on a suction ring and you can mount the knife in it and it follows a really nice tangential curve around. So all kinds of little gadgets to do arcute incisions. Another really important concept is thinking about shifting the location of your cataract incision to correct astigmatism and making a deep groove for your cataract incision. You can act like a limbo relaxing incision or an arcute incision. A lot of these can be done in the clinic. Pitfalls, lack of perpendicularity leads to shallow incisions and poor effect. So that knife, you're setting it very precisely. You want it to be poking as far into the cornea as you can to achieve depth but not perfect. This is actually, I actually saw a guy yesterday, believe it or not, with an epicaritofakia graft and I haven't seen one for probably 10 years and I'm like, okay, it's in my lecture. But this was used way back in the day for aphakic kids before IOLs were commonly put in kid that was used for other conditions but it's basically just taking a piece of tissue and grafting it onto the front of the eye and it rarely will see that. So historically could be interesting but almost never see them. Intax are important and hopefully most of you have seen an intax patient by now but it's just a plexiglass ring. You kind of see them in this picture here. Threaded into the cornea. We all know from the first lecture the average corneal thickness is low 500 microns. So that's half a millimeter. So we have to precisely thread that into a half a millimeter space without perforating anteriorly or posteriorly. So good thickness measurements, accurate surgery is important. Femto second lasers can do that really well. We also often do intax with a manual surgery and I did it in my original, I couldn't find the video but I had a video of it and it actually I think works better than the femto second laser because it's a steel disector that goes in and it kind of stays within the same lamellar plane throughout the cornea. So if you think about a carotidoconus cornea it's gonna be thicker, superiorly and nasally and temporally and generally thinner inferiorly. And so you kind of like if you're starting at a certain depth, the manual disector will stay at a more constant depth. So if you're like 60% depth you're more likely to kind of stay in that same plane. Whereas a femto is just gonna cut a constant depth away from the surface. So it's another really, really important concept. So how does a carotome or a femto second laser work? You guys ever thought about that? How does it get its reference point? You should all go to the iBank and maybe during the cornea rotation you should do a little field trip to the iBank and watch them use a carotome to prepare desectition. But does anybody know how that works? How do you achieve an appropriate depth? It's like a deli slicer. You smash the cornea flat and then the laser or the blade, if it's steel, is just programmed a certain depth away from that. So if you think of that deli slicer and the black forest ham going across that little gap that's exactly what we do with our lasers. So with a laser it's a plastic dome. With a, and in the case of you could even apply this to femto cataract lasers. Some of them aplinate the cornea like the catalyst laser actually has a water bath. But it's just referenced to a particular depth below the surface. And so that's, so you can think of if you have a cornea that's really thin inferiorly and you're smashing it down, you're gonna be cutting maybe 80% depth inferiorly and maybe 60% superior. So a lot of these are just physical concepts of just introducing them. You don't have to really remember all this stuff. But our ideal achieved depth or desired depth is about two thirds depth. These work pretty well to stabilize keratoconus. I would say on par with cross-linking. A lot more invasive than cross-linking. We pretty much just use them. They were originally approved for myopia but we pretty much just use them for keratoconus. We generally don't get people out of their contacts but sometimes can get a person out of the hard contact and into a soft contact. And generally if it's not like, if they have scarring we don't usually do intact. They can erode or extrude as in this case. They're placed too shallow. They're generally pretty darn safe. They're removable. One nice thing about intax they're super easy to remove. Even if they've been in there for years you can just cut down right on the end of it. At the slope lamp and grab it with the Zinski hook and just pull it out. This LTK thing is, I mentioned it's not really done. Even CK which is a little wire needle that's stuck into the cornea and heats up the collagen it's really not used that much anymore. Again, conceptually it kind of just emphasize what we're talking about today. If you're heating up the collagen and creating a flat spot in a ring around the cornea it's gonna dome up the center. So flattening locally, steepening adjacent and it's a treatment for hyperopia and presbyopia. If you know that much, you're good. And then kind of like other surgeries, all of the surgeries that we've talked about the optical zone titrate CFA. So more rings, smaller optical zone, more effect. Problem with this surgery is regression. It doesn't hold. Some people have talked about trying to combine this with crosslinking to see if that will work. But hyperopic laser treatments have just gotten so much better that people kind of lost interest in that because the LASIK and PRK are so good for hyperopia. Now the lasers have gotten a lot better. So again, regression. Yeah, it's a good time to stop for questions. Any questions so far? We've got about 10 minutes left. Clear as mud. So this, some of you don't even, you know, pretty much everybody's seen Pachymetry and Glaucoma Clinic, but ultrasonic Pachymetry is still the gold standard even with OCT-based Pachymetry. I mean, this is probably the most accurate. Although machines like Pentacam are really, really good too. So optical Pachymetry is pretty darn good. And know that the accuracy is probably about plus or minus five microns. So we're gonna talk a little bit more about some of the clinical considerations. Just kind of putting it all together. As far as when you start, get out in practice or, you know, if you do a cornea fellowship or whatever you're gonna wanna try to, okay, figure out what patients can I treat? What do I need to watch for, et cetera. And again, as I mentioned at the very beginning, it's really avoiding pitfalls is probably three quarters of the battle. And informed consent is super, super, super important, more important for elective surgery. When I was at Academy in October, I attended one of their multiple sessions, but it was one of the kind of medical legal risk sessions. And it was in cornea or refractive day, I don't remember which one, but the amount of malpractice litigation for refractive surgery is probably one-tenth of what it is for cataract surgery. It's surprising, isn't it? And why is that? That is just because it's a completely different process. You know, early on it wasn't that way and there were some really big lawsuits. You know, there's a famous lawsuit of a, I think it was America West back when that was an airline pilot who got like six million bucks because he had eight millimeter cupors and even though he turned out 2015, six million dollars doesn't sound like a lot nowadays, but he was 2015 uncorrected but had enough night vision side effects that he didn't feel safe flying and so it was awarded six million dollars. And you know, the surgeon didn't really document good informed consent or pupil measurements. And so I mean, it was appropriate in my mind, but because there have been kind of these sentinel cases and refractive surgery is just a different animal, the informed consent is so much better. The consent forms, the documentation, everything is more bulletproof in terms of lawsuit type stuff and the surgery has just gotten so much better in the last 20 years that outcomes are really, really good. So you're much more likely to get sued by that 2030 cataract patient that you don't get quite where you wanna get them and maybe said, yeah, you got a cataract, it's blurry, let's take it out. And they say, well, my dry eye got worse and I can't see and you didn't talk to me about a presbyopic lens and all this stuff. Then, you know, a laser patient that maybe doesn't have a good outcome because you've already covered all of this important information with them. And complications are actually really uncommon too. It's really important in some of these informed consent things to have some kind of interactive informed consent with patients typically watching a video, taking a quiz. I mean, that's something that actually kind of malpractice investigations want to look at and say, yeah, you showed them that they signed a piece, you know, they didn't read it. They said they didn't read it. But if you have a quiz and they said, yeah, they did because look, they wrote on my quiz, they watched this video, they wrote on my quiz. I mean, that actually really helps. And so that's important. We probably actually need to do that with our cataract patients too. If it ain't written down, it didn't happen. You guys know that, you know, and EMR is, it's one of the things I love about EMR because you never want to go back and change your note, especially after the subpoena shows up. But it's okay to go back and bolster your note. If you find a note, and even as a resident, if you find a note and you talk to the patient and you said, hey, I'm a little worried about your patient, but I'm gonna use Dr. Crandall as an example because he's not gonna do it, you're gonna do it. I'm a little bit worried about your patient. They don't really know if they want distance or near and I talked to him about it. Go in and put that in the note to say, you know, patient didn't really seem to understand. I mean, it's really, really important. It's really helpful. And EMR is awesome because you can kind of go in there and see what's happened. Look at the telephone encounter, see what questions the patient had. They really want to prepare because you really shouldn't be documenting after the procedure's done. But after your initial visit, if something comes up or you're thinking about something, call the patient, type a new note, whatever. Yeah, we don't really, I tend to just operate in terms of statistics. You kind of have to know what your outcomes are in order to educate patients. If you don't know what your outcomes are, you can't educate patients. It's not informed consent. So you just need to kind of know how your patients turn out. You just share that and say, okay, I've been doing this for 25 years. Never had a patient go blind. You know, I do 5% enhancement surgery, whatever. So this is like the most important thing to know about LASIK surgery is dry eye. And there are a variety of factors, but especially in Utah, I spend more time dealing with dry eye and vision correction surgery than anything else. And because dry eye has such a high prevalence here. I mean, it's just super, super common. Why else might a dry eye don't look at the very bottom bullet point be such an important thing in refractive surgery? Is it because they're self-select, they're not able to work on that? Oh yeah. Yeah, I mean, I can't work contacts because they're uncomfortable, right? And so I want to get LASIK. So I come in and have LASIK and you cut all my corneal nerves and you create a slightly irregular surface. And then I'm really hurting, or not hurting, but I just can't see because my cornea is denervated and it's got three plus punctate care top. So we do a ton of PRK in Utah. Partly because we're adapters, adopters of PRK, but also because dry eye is more common with LASIK. Although there was a military study recently, which was performed mostly at Southern, can't remember if I, I think it was multiple service branches that actually was based on questionnaires. It wasn't a bad study, it was a pretty good study, but in young military population and their dependents, they actually found that their PRK patients had more dry eye symptoms and findings. That would not be reproduced here in our population. LASIK is definitely worse. And it's because mainly of the denervation effect. Really important, treat it preoperatively, do PRK. Some people think that there's a lot less dry eye with femtosecond cut flaps as opposed to keratone cut flaps. I haven't seen that, but we have a Dunnian keratone flaps for 10 years, so I don't know for sure. Herpes, we'll backtrack and we'll cover a little bit more of this on the next lecture too, but I'm just gonna run through a couple things so you can think about them until next week. So think and learn a little bit about herpes and refractive surgery, because it's super, super common. HSV is super common. And you don't wanna have a herpetic flare up in an eye with refractive surgery. Does that mean you can't do surgery on people with the history of herpes simplex keratitis? I want you to read about that. You can answer me. Keratoconus, that one's kind of a no-brainer. Until recently, when collagen cross-linking has been approved in the US now. And so people are actually doing even LASIK, but PRK on cross-linked corneas. So we'll talk about that more. There's your crab claw again. This is not quite the D, but sometimes you'll get kind of a D shape. You kind of almost see. There's more keratoconus. Refractive surgery after corneal transplantation can be really useful for anisomotropia and contact lens intolerant to patients and patients who are young and faking. So, something to know. See, this is a really important one. Anybody who's interested in going into glaucoma, I want them to read up a little bit on this because I'm gonna quiz them a little bit next time. So refractive surgery, corneal refractive surgery in glaucoma. Retinal disease, anybody who's interested in retina, read up on this a little bit. How does retinal disease, because a lot of these will be higher myopes, how does that correlate with vision correction surgery, particularly laser surgery? We're not talking about intracurricular surgery. Ambliopia, anybody who might be interested in beads will have to get Julia on that one. Say Julia, read about ambliopia refractive surgery. And then that's enough for today. So, thank you. Any other questions or anything? So just learn about the physical stuff, really the shape, the techniques, that's really what you need to know. That'll apply to anything to do with retina. And you can write about RD, ART-Retinal-Tair and LASIK and PRK and stuff like that. Thanks again, guys. I'm really apologize.