Lecture: Interpretation of Corneal Topography

This lecture discusses the evolution and principles of corneal topography in this lecture. In addition it helps the attendees understand and interpret topography maps from different commercially available topography units, and discusses the strengths and limitations of different topographers in clinical practice.

Lecturer: Dr. Aravind Roy


(To translate please select your language to the right of this page)

DR ARAVIND ROY: Hello, everybody! So we shall be discussing corneal topography, its interpretation, and its use in day-to-day clinical practice. Let me start this discussion by introducing myself. I am Aravind. I have completed my corneal and anterior segment fellowship from the LV Prasad Eye Institute, and I’m currently working at the Kode Venkatadri Chowdary Campus in Vijayawada. We have no financial disclosures or conflicts of interest. While I start off with the discussion, maybe it’s also good to have your current positions in which you work in ophthalmology, and this talk, while not focused on this question, will be very interactive. We will take questions in between. I would encourage all of you to put forth as much questions as possible. We’ll make a discussion, and then we’ll try to clear the concepts one by one, and subsequently, we’ll proceed. Okay? Okay, good. So I’m just getting the results now on my screen. So most of us are ophthalmologists. And out of which we also have some residents in training too. That’s great. So I’m sure all of you will be using topography in your practice. So the corneal film air interface provides two thirds of the vergence of the eye. And it also plays an important role in the quality of the optics of the eye. A small amount of surface distortion will reduce the quality of the image. So it’s important apart from the refraction to understand what’s happening in the eye and why the quality of the eye is affected, if at all. So we started with the (inaudible) disc, where the light onto the cornea was used to localize broadly which areas of the cornea were distorted. And then from that evolved the Placido disc, which is basically a cardboard disc with alternate black and white circles, and a central opening, through which the observer can observe the cornea, and from there, keratometry, in which a ring of lights is thrown onto the cornea, and distortions are analyzed. So when we look at distortions from a normal cornea, this is normally how it will look. Some areas may be circular, concentric. Some may be broad, and in some areas, there may be crowding of those things. So what it means is that when the mires are farther apart from each other, larger in diameter, broader in width, that is a flat corneal profile. And those areas which have a higher power, the mires are smaller, crowded, and narrower in width. However, there are several limitation of Placido-based systems. So one is that there is no analysis of the posterior surface. There is no representation of areas of thinning. There are limited data for scarred corneas. And this coverage is limited to the anterior 9 millimeters of the cornea. And there’s also a high incidence of false positives. So that led to the development of newer technologies, which was aimed at accurately measuring the cornea, and also getting more accurate information from the surface of the cornea, but in addition to the surface of the cornea, the anterior chamber, and so on and so forth. So the next generation includes instruments that include the Orbscan, the TMS, Galilei, and the Sirius. So the Orbscan uses the slit, but it also has the reflective technology to analyze the surface. So when we have angular reflected light, the angle between the two gives an estimate of the slope. And the backscatter, taken up by the analyzer, gives the height. So these are important concepts in corneal topography. Slope versus height. At this time, I would like to pause and maybe take questions from people who are participating. Whether they would like to take some further discussion on slope versus height. Because these are the two parameters from which the corneal topography depends. Slope is where the topo is at the point of height, how much the reference point the cornea is set. So any questions, anybody? Okay. So while you may be typing in your questions… So the slope of the gradient, basically, how the cornea is at that point of the cornea which is being imaged, whether it be peripheral or central cornea — the height refers to a reference plane, which traditionally is considered the sea level, and how much above or how much below the sea level that point of cornea, which is the image, is. So we shall be looking into all these concepts in a little more detail in subsequent slides. In addition, whenever the cornea is imaged by a slit scan, the lens which images the cornea is oriented that the objective image comes into focus. This is true in theoretical physics. However, if one of the surfaces in the object has retinitis, then something like this would appear. There is a depth of focus, and one point will be nicely focused into the analyzer. The point which is ahead and the point which is behind will be blurred. So the Scheimpflug principle was introduced, where it’s taken into the calculations that the lens is tilted in such a way that the object and the image are perfectly in focus. Okay? All right. So it’s important to understand the Scheimpflug, because the technology takes into account the Scheimpflug. It calculates the more accurate figure. When we take topography and we want to calculate, it is always considered that what is measured is more accurate than what is being calculated. Okay. Any questions at this point of time? Okay. So when the slit scan measures the anterior chamber, it measures various important parts of the anterior segment. That includes the air-anterior cornea interface, the posterior cornea, the lens, the anterior capsule of the lens, the iris, the projector reflex, the fixation reflex, and of course, the limbus. All of which has significance in surgery, and in the case of pathology. Now, whenever the data is put forth, it’s important to look at the scales by which the data is coded. So this is actually given as output in falsely color coded maps. The color coding is basically for ease of interpretation and understanding. And we also need to understand that these scales are in several steps. Now, we basically have this map, which has an anterior and a posterior. Okay. And there are… Okay. So there are several… There are several scales that you see on both sides of the map. So in each falsely coded color map, it has different scales, and they have different intergradient steps over there. So let us take into account this keratometric map, which is on the bottom left. So it has 1.5 diopter steps here. So between each small box, there is a step of 1.5 diopters. Now, we can manually adjust these scales, and as we decrease or increase the scales, the way the map appears is quite different. So when we make it 2, then the map appears to be in 2-diopter steps, as we see here. And this is the default scale. So when we have larger steps, they are much more specific. And when we have smaller steps, they are much more sensitive. So I’m going to run you through this step once again. Okay? So look at this. So when we have 0.5-diopter scales, we see a cornea which is very steep. Has a lot of astigmatism. But actually, it’s the smaller steps, which is very accurately measuring the point to point difference between different cones of the cornea. But as we increase the steps, they become much more lighter, almost resembling a normal cornea. So whenever we are interpreting a cornea from a topographical map machine, we need to see what are the steps and how the color coding is done. So larger steps, more specific. Smaller steps, more sensitive. Okay. So when we do the color coding, the reference coloring is green, and anything which is red shifted is steeper, or those which are more flatter are blue. Which has been altered by a blue shifted coloring. So elevation, similarly, the reference level is considered to be normally by tradition to be green in color. And those which are anteriorly lifted are red and those which have a posterior relation are blue. So those which are higher areas, anterior to the reference surface, are coded in red, and those which are posterior to the reference surface are coded in blue. Red can be high or positive, blue can be low or negative. Similarly, the pachymetric maps are also coded. The thinner ones are coded in red color and the thicker ones are coded by blue color. These are international conventions, and this is used almost universally from all the maps that are clinically relevant. So at this time, we’ll take questions. And any other additional doubts or any queries from your end would be most welcome. Okay. Yeah. So most of our viewers have clicked it correctly. It provides a graphic representation of the data. It’s important to look at the steps. It is falsely coded by internationally accepted criteria. So we also have a question. So let me read that out. So one of our viewers was requesting that — what about the steps that I was discussing about? So just a quick recap. Okay. So every topography map, if you see one like this, over here, is by convention given as a printout, as these maps. And each map will have a color scale by its side. Each color scale is unique to each particular map. The anterior float has its own color scheme, so is the posterior float, the keratometric map, and the pachy. So these boxes are the steps by which each color is denoted. For example, 26 denotes a very flat cornea, and 58 will denote something which is on a steeper axis, or steeper part of the cornea. And normal is 46. So between 46 and 50, there are 4 or 5 steps. So each step would have about 1.5 or 2. So when we are interpreting the maps, then we need to interpret them by how many steps are there in two readings. So if there are larger steps, they are 2 diopters. And if they are smaller steps, the map would appear very different. Okay? I hope this answers your question. So smaller steps are more sensitive. Larger steps are more specific. Any other questions at this point in time? Okay. So I’m going to proceed to the next. So the normal cornea has a central steepening of the normal cornea, and there is an annular seat. Annular sea. If you look on the cartoon on the left, it has a blue colored hemisphere. This is the reference here. From which the calculator calculates the actual shape of the cornea. And the yellow line is a normal cornea, which is a related shape. So when this is fit over the hemisphere, then we see that the central cornea is much sharper or steeper, and that produces a central hill. Okay? And the midperiphery is actually much flatter. As you’ll see, this yellow line going — beneath the reference surface. So that produces an annular sea. And this is again steeper, so it produces the peripheral highlands that you see on your left. So this is how a normal cornea would look on the topographic map. Central hill, annular sea, and peripheral highlands. And the topographics of this, of the cornea, normally has against the rule astigmatism. So one axis would be flatter, and one axis would be steeper. So that would produce a central saddle, and one area would be flat, and as a saddle, the other area would be raised. So that would produce this kind of topography on the keratographic maps. So are these two concepts clear? We can take questions at this point of time. If needed. Okay. So these two patterns that we see on topography are very normal to the cornea. A normal cornea. And this is important to understand any abnormality or pathology. So a normal cornea would have the central steepening, with the peripheral annular sea and four peripheral highlands, and from the astigmatism point of view, it would have a central saddle. Okay? All right. So traditionally, the output from any topographer that you use, anything, this is the Orbscan, but anything that you use would have four maps, and this quad-map view typically has the anterior elevation, a posterior elevation, a curvature map, and a pachymetric map. Which is this one. Okay. I’m going to pause over here for any further questions. Just a minute, everybody. I’m just trying to get my slides. Please bear with me for a moment. Okay. So here we go again. I’m sorry for the interruption. We also have a question. Okay. So we have one of our viewers who asked the definition of elevation. So yeah. So if I go back to my previous slide over here, elevation will basically mean how much above or below the reference surface one point of the cornea will be. So if you look at this part of the cornea, so the yellow line is the cornea. And the blue hemisphere is the reference surface. So every unit, every topographer, will have its own reference surface. And anything which is above the reference surface is steeper. Anything which is below the reference surface is flatter. So elevation will mean basically how high or how low above or below the reference surface is that point of cornea which is being imaged. So if you look into this concept, on your right side, the cartoon we’ve just seen here, the central area is higher than the reference surface. This is coded by red. The paracentral cornea is below the reference surface. So it is coded by blue. And the peripheral highlands are, again, above the reference surface. So they, again, show us — four peripheral highlands. I hope that answers the question. Okay. So proceeding with our discussion again, so every output from any topographer usually has a quad-map as its output. And it typically has the anterior elevation map, the posterior elevation map, the curvature, and the pachymetry. And in addition, there is a lot of data which is shown in the middle or below, depending on which topographer you are using. Typically, every topographic map would have its own scale by its side. So as you can see here, you have a scale which is typical for the anterior floor, that is in microns. So it is similar for both the anterior and the posterior elevation maps. The curvature would have the diopteric power, so that is shown by this, from 26 to 58 diopters, and the pachy is in microns. There are several other parameters, such as the keratometry, the 3 millimeter zone irregularity, the 5 millimeter zone irregularity, the white to white, the thinnest pachy. This is the Kappa. Are there any questions? I think somebody popped a question now. Okay, yeah. So we have two questions now. What is posterior elevation, and why it differs from anterior. So posterior elevation — the cornea typically will have anterior reflective surface, which is the anterior cornea, and the light that is scattered off the anterior surface is used to construct the anterior floor. Orbscan does not measure the posterior surface, but it actually calculates it from the anterior surface. And then produces a posterior elevation map. And some Scheimpflug-based topographers would actually measure the posterior elevation map. And in addition, some other technologies like the Cassini, measures both anterior and posterior surface of the cornea. Every topographer would have a nomogram. On this nomogram, the reference surface is calculated. So that nomogram depends upon the study population from which the current general topographers are standardized. So, for example, the Orbscan would have a standard reference surface, and then the cornea that is measured from the patient is actually superimposed onto the reference nomogram. All the reference values for each point that is imaged. And that point is then calculated against the nomogram to see whether that point falls within the normal part, what is expected for that patient at that age, or whether it is higher or it is much steeper, or it is more flatter or it is at a lower elevation. So I hope that answers your question. So that reference gives us that whether these points are actually above or below the reference surface. Can we compare the elevation map to standard deviation in orthometric visual field? Yes, I would agree with you. So this would definitely compare to the pattern standard deviations, just as each point would be from the nomogram, so also in the Orbscan, there is a reference, and any point which is above that best-fitting sphere or below that best-fitting sphere would accordingly be higher or lower from what is expected to be normal. So let us take this example here. So if you look at this point of the cornea, I’m sorry… So if you look at this point of the cornea, this point on the posterior floor is actually higher than what would be normal. And this point, which you see this little island — it is actually flatter or lower than what is the normal. So automatically, the green areas are the normal, and you can actually visualize in a 3D construct which area of the cornea is steeper and which area of the cornea is flatter. As for us, the posterior map — oh, we have one more question. Let’s see that. So what are the normal values for the anterior and posterior DF? What would DF mean? Could you please clarify? Okay. So while we wait for the response, so normally, the normal values are somewhere around 44 or so. So at this point, at the paracentral cornea, anything that is in those data, denoted by… They are denoted by the green color coding, and similarly for pachy, it could be somewhere around 400 to 500 microns. And similarly for the keratometry, the green is denoted by 42. So you need to actually look at the color code and see what is zero. So all that is zero is the reference surface. All that is red is above the reference surface, and all that is blue is below the reference surface. Yeah. I hope I answered your question. So you basically need to look at the color codes over there. So the best-fitting sphere is very typical for one particular unit, one particular topographer. And the nomogram will vary from topographer to topographer. That’s the reason that when we do corneal topography, it’s best that you do it in the same machine. So that whatever is the interobserver — known as intertest variability, test to test variability, is minimal. And when you are actually looking at the cornea, with a condition such as keratoconus, you will actually very accurately know if you have measured the topography prior to that. Meaning that if you have measured the topography about a month ago, and then you remeasure the topography in three months’ time, then basically you need to measure those in the same machine, and see whether there has been any change in the measurements. Okay? I hope that answers your question. So in a nutshell, all topography outputs have a quad-map, which will have the anterior and posterior elevation, and the curvature, and the thickness. It will have a color scale. The green will denote the reference, roughly. Anything which is above or below are the elevation maps. So that will say what is the height of the cornea, above and below the reference, at that point in time. Blue is below sea level. Red is above sea level. And keratometry would be the curvature of the slope, and how steeply it is sloped at one point, and how flat it is at one point, again, denoted by your color codes. Curvature, as well as elevations, are based all on nomograms. The nomograms are typical for a unit, and one needs to measure the patient in the same topographer, ideally, so that you can serially follow the patient, and see what will be the progression, if any, if you are looking at the corneal condition. We have one more question before we move to the next. Okay. The example that I am showing — yes, that would… This would be a normal cornea. Yes, you’re quite right. Yes, that’s correct. So it’s very nice to interact with you. And it would be even more… Better if you asked all questions. Any doubts that you will have, which you face in your day-to-day practice. Because for the uninitiated, it would be definitely quite difficult to navigate through this bizarre pattern of colors, the different varieties of the machines that are used in our office, and so forth. Every patient will bring topography measurements from some place, and they’ll request the treating physician to make some sense out of it, and whether they can help us interpret whether they have the pathology, or they are a fit for refractive surgery, and so on and so forth. So if you break it down to these quad-maps, see what is happening, which areas are elevated, which are not, they can inform the physician about the patient’s management. So I will pause here with a short Orbscan map, which are two serial maps of this teenager, who presented with eye allergy. So her presentation in January 2011, this was the left eye scan. You can see both the anterior and the posterior floors have a lot of high points, which is also corresponding on the keratometry map, with asymmetric curvature and thin pachy. When we did the Orbscan a year and a half later, this is what we saw. All the parameters have changed. And if we look at the max and the min, the keratometry — I would like viewers to focus on this part of the screen. The max and the min. Yeah. So here you see the max is 51.9 and the min is 47.5. And you look at that. In the immediate next Orbscan, see what has happened. The bow tie has flared up, and the maximum has increased by a lot of points here, from 51 to 57. So obviously this is a keratoconic eye, and it is progressing. So viewers can put forth this question. Before we continue with our discussion. Okay. Yeah. So the response that we got out — the majority believe that — all of the above. Yes, we should advise for collagen crosslinking, it is important to consider the age of the patient, avoid eye rubbing, and all of the above. So most of the viewers have responded to the last point, which is all of the above. Which is actually true. So I’m going to go back to the scans which I have discussed with you. Okay. So this is the first scan. And just look at the next one. Yeah. So we have one more question. Please keep looking at that. I’m going to come back. Okay. So one of our viewers has asked us… What are the features of keratoconus topography? Good question. This is what I want to discuss right here. So look at the quad-maps over here. So what we see over here… From the topography, is that we have one central highland which is very steep on the anterior float. And corresponding to another area on the posterior float, which is also very steep, and these are shown by these red colors. Similarly, we see on the keratoconic map a red asymmetric bow tie pattern. So if you look at this Orbscan, basically you see one small plus, which the optometrist who has taken the Orbscan has gone over here, to give the printout — to show this is the thinnest point, and all the four maps have the same area of pathology in the same part of the cornea. This is not just true for the Orbscan. But it is also true for any topographer that you use. Look at the cornea. Look at the anterior and posterior float, if there is any. Look at the keratometry and the pachy. Usually the keratometry and pachy will be there. On the anterior float, the keratometry and pachy will be there. The topology corresponds in three of the four maps. Yes, it does. So if it corresponds, basically what we are looking at is one localized area of pathology, which is having a higher elevation. Which is causing an abnormal keratometry, and which is also causing corresponding thinning of the cornea. So if all these four match, and all of these are in the same point, then probably this is what we are looking at — is a keratoconus, possibly. Now, in addition, what else we should look for, when we are looking at the keratoconic eye? Most importantly, it’s important to look at the patient. And see whether this profile matches that of the keratoconic patient. Typically, keratoconus is a non-inflammatory ectatic corneal condition. Affects young adults. More males than females, and particularly in the teens, and it continues to progress until their 20s. So if patients are in their 20s, or in their early teens, they are more likely to progress. While there are several risk factors, the most established risk factors are compulsive eye rubbing. So if the patient is an eye rubber, then we should advise the patient not to rub the eyes. Because the mechanical force may induce progression. The age, the hormones, as well as the age of onset are also important. Meaning that if a patient who has been detected with keratoconus early on in life, in 10 or 11 years, then that patient has a much higher chance of having more advanced keratoconus by the time of reaching the age of 20, as compared with someone who was detected later on in life. Similarly, if we see a patient who is in their early or late 20s, we know that keratoconus only progresses up to the age of 30 years or 32. Progression, while it has been documented or reported beyond 30, is low, or it’s much more slowed down at that point of time. So while you as a physician may not be very aggressive at that age with many patients in the mid to late 20s in crosslinking or controlling this condition, as compared to a patient in their younger teens or at an early age. Okay. So I hope that answers your question. Okay. One of our audience has asked that do Pentacam maps — differ from Orbscan maps? We will definitely be discussing Pentacam, subsequently. We will be discussing a lot of other features too, in addition. So Pentacam maps do not differ a lot from the Orbscan, except that their references are different. Their color coding is pretty much the same, because these are international conventions. Pentacam also ideally are shown as quad-maps. So I’m trying to… You know, share with you or discuss that no matter what your output is, whether it is an Orbscan or a Pentacam, the basic principle remains the same. What we are looking at is as a physician, in a patient who is having keratoconus — you will probably not advise surgery in those cases which either progress or those which are borderline. And you may advise a crosslinking procedure if this is an early keratoconus, and there’s a high chance that there will be progress. So yes, Pentacams are very different from the Orbscan maps, but having said that, the basic outlay is the same, and the person interpreting those maps also do the same as any Orbscan or quad-map output. So to progress with our discussion… Okay. Some other conditions may also, in addition, some other conditions may also, you know, mimic a keratoconus. These would include contact lens warpage, misalignment, dry eyes, or external pressure on the eyes. Another important corneal keratoconic condition is the pellucid marginal corneal degeneration. This is also fairly common, and like keratoconus, it has been reported to cause corneal hydrops. It needs to be closely followed up. Those eyes need to be protected. And the classic appearance is somebody who would come with a very poor vision, early on in life. Sometimes it appears on the slit lamp. And the topography map shows a butterfly. As you can see on the picture on your left. So this is how an Orbscan would look. It would be like a butterfly, or sometimes it is called a crab claw. Like the claw of the crab. There is a lot of against the rule astigmatism, and there is an area of pathology. In keratoconus, the bulge and the thinning are at the apex of the cornea. In contrast, in pellucid marginal corneal degeneration, the bulging is above the area of thinning, but the corneal thickness is same. So this is what is also denoted in medical parlance as the beer belly, basically. So there is a thinning and there is a bulge above the thinning. Okay. Some other common corneal conditions are the Terrien’s marginal degeneration and keratoglobus. So there is no characteristic topographic features. There is a lot of steepening of the cornea, which is typically from limbus to limbus, and there is also a lot of corneal irregularity. And there will be typical perilimbal corneal thickening and a higher amount of against the rule astigmatism. okay. So I can take some more questions over here. If anyone is interested. And then we move to the second interesting part of our discussion. That is: How do we choose a topographer for our practice? Okay. So while I proceed to the next… Maybe could you answer this question? How many of you use topography in your working practice? Okay. Oh, great. So almost 50% of our viewers use topography. And 50% don’t. That’s great. It’s 50/50. So I’m sure this discussion is helpful. You can reach me via Lawrence, or contact me for subsequent webinars, over here. And we also have a question. Okay. Okay. So one of our viewers has asked that they have helped their patients by asking them to open their eyes widely, and seeing whether, if I understand, help them with their fingers. The patient is asked to… Widely open the eyes, with the help of fingers? I would probably not advise it. Because even small subtle pressure on the globe may cause distortion of the cornea. Okay. And the people who have answered yes from the previous question… Would you quickly take down this question also? That what is the normal topographer that you will use in your day-to-day practice? Okay. So most of our viewers use the Pentacam. Yeah, that’s very, very common indeed. Pentacam is quite common in clinical practice. And it’s also on its way to become the clinical standard. It’s also good to see that there is also a variety of other… So 40% of our viewers use Orbscan, and 67% use Pentacam. So I’ll be giving the next part, give an introduction to it, and then I’m going to pause, because we’re at the end of our time. And I’m speaking on aberrometry next Friday. I’m going to conclude this talk at the next slide, and then talk about the different topographers, and then talk about aberrometry, on our next. So viewers are requested to join for the remaining part of the discussion on the next Friday time slot. In your respective time zones. And we will discuss on that the different types of topographers in different clinical use, the advantages, and the disadvantages of each, and how you can build your practice, depending on which topographer you need to choose. There are different topographers in the market, which is currently available. The basic principle differs from topographer to topographer. And they may be typically either reflection based, which is keratometry, photokeratoscopy, or videokeratoscopy, projection-based, Scheimpflug-based, spot reflection-based, or hybrid topographers. We have about five minutes before we end our discussion. You need to choose your topographer, basically, depending on what practice you do. If you are primarily a refractive surgeon, the Pentacam, Galilei, or Placido-based topographer may be helpful for you. Because they are good for patients who are more prone for refractive surgery. In addition, if you also have a practice which is more cataract surgery-based, and you do a little bit of refractive surgery, maybe, then probably you will need an aberrometer, in addition to the topographer. So in this, the Orbscan, the OPD III, and the iTrace may help you. So I’m going to stop here, take questions, and we will discuss the remaining part of topographers in our next session, on the coming Friday, and in addition, we’ll also discuss aberrometry. We have one question. So you advise crosslinking for young patients with keratoconus… So I would not really advise automatically, but yes, if the patient is prone for progression, then probably it makes sense to do a crosslinking procedure early on. But having said that, there are several factors that you need to look on. For example, when you see a child who is also keratoconic, one needs to see how severe is the keratoconus, how much of the pachymetry is there, that means the cutoff for keratoconus is 350 microns, at the thinnest part of the cornea, and you’re seeing a child who is 10 or 11 years, and his pachy is somewhere in the range of 350 to 400, you will definitely be more aggressive in treating this keratoconus, because there is a high chance of this child progressing. As opposed to someone who has a fair amount of pachy, moderately steep cornea, and maybe a little elder in age, say 20 or 21. Those in the high risk groups are compulsive eye rubbers or a history of ocular allergy, so they habitually rub their eyes. These are cases where you control the allergy and definitely advise to do the surgery. One more question is the difference between Pentacam and Sirius. So these are basically two topographers which use both Scheimpflug systems. The Scheimpflug principle is used to characterize the cornea. However, the outputs in addition definitely gives some other advantages in terms of measuring the best fit corneal surface for putting a contact lens — it helps you measure the topography. So there are some other data points in addition to topography. So from manufacturer to manufacturer, there are several data outputs, which differ from machine to machine. So depending on each individual’s practice, you need to tailor made which topographer will be most relevant or useful in your practice. There is not much difference as far as topography is concerned, because the principle is the same in both. Okay. So I think we are coming to the end of our time slot. And we’ll definitely meet next week. Next Friday. And thank you very much for being with us over here. And I hope it was a productive discussion. If you have any questions, please send it to Lawrence at Cybersight, and he can forward all of them to me. And carry on. Okay. Thank you very much.

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January 27, 2017

Last Updated: October 31, 2022

8 thoughts on “Lecture: Interpretation of Corneal Topography”

  1. That was a informative presentation. Thank Dr. Aravindh. I couldn’t find the second part of the lecture of this same presentation. Any possibility to get the link please?

  2. Orbscan/Topography is recommended in cases where the corneal surface requires mapping so as to detect keratoconus, study the shape of the cornea for suitability for refractive surgery, stability of the cornea after refractive surgery or collagen crossliniking, examine the astigmatism post penetrating keratoplasty, cataract or limbal relaxing incision and suitability of the eye for phakic IOL implantation.

    • Orbscan/Topography is recommended in cases where the corneal surface requires mapping so as to detect keratoconus, study the shape of the cornea for suitability for refractive surgery, stability of the cornea after refractive surgery or collagen crossliniking, examine the astigmatism post penetrating keratoplasty, cataract or limbal relaxing incision and suitability of the eye for phakic IOL implantation.


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