New Modalities

Round Table

What can wavefront technology do for my practice?*

Daniel S. Durrie, MD, moderator

Dr Durrie: I’d like to work with the panel a little bit. We didn’t talk ahead of time about how we are going to do this, but the question posed in this round table was, “What does technology really do for my practice?”* I have been working with several of the companies in this area for the last year and a half. I have tried to answer this question a little by using this with patients, and trying to figure out what the technology can add to what we already know. The way I look at it is that we’ve had Placido disc technology, which has been there for quite a while and has given us a certain level of information. As we started to move toward looking at elevation, I think that OrbScan plus other topographers drove us a little in that direction, and we are starting to look at heights in elevation. That gave us slightly more understanding. I started looking at that as more the shape of the eye, rather than just a bunch of colors. In my mind, I have looked at wavefront as giving me the shape of the optical system. It may be an odd way to look at it, but it means it is not just the cornea and the shape of the front of the eye, but essentially it is looking all the way through the eye and what happens to each light ray as it goes through the system and where it ends up, and once we look at it that way, how it really affects vision. Then you have to correlate this slightly with the things we already know. And I am going to emphasize this a little this morning. A lot of you are familiar with OrbScan. OrbScan gives you a bunch of information. Down in this area, it can give you the thickness of the cornea across the cornea, usually thinner in the center, and you can see the thickness there. Then this is a best fits sphere elevation map of the posterior surface, and this is the best fits sphere map of the anterior surface. Best fits sphere basically says that green is a spherical surface and anything that is yellow is kind of above sea level or closer to you than that, and blue is below sea level behind that. This is a Placido disc topography. In this particular patient, if you looked at that, it looks pretty normal, but there is some irregularity. This is a patient who is just coming in for refractive surgery. If you looked at a high order map of this eye in 2D and 3D, just taking the Zernike polynomials and putting them in a mathematical program, what comes out is kind of a new look for us. We have had these other ways of looking at things, but this is a different thing to look at. Now what we have to look at is what does it really mean clinically. Does it add information to what we already knew? This is trifoil,

*Dr. Durrie was unable to provide the graphics for this material.

Wavefront and Emerging Refractive Technologies, pp. 55–63

Proceedings of the 51st Annual Symposium of the New Orleans Academy of Ophthalmology, New Orleans, LA, USA, February 22-24, 2002

edited by Jill B. Koury

© 2003 Kugler Publications, The Hague, The Netherlands

and you will have heard of these terms around, and you can see that there are three bumps which you can see in the 2D map.

So I am going to go through some cases here and discuss them with the panel, and then we will open it up or I will call on various people. How would any of these clinical cases give you some idea, from looking at the wavefront, of whether this patient has symptoms or not? I will give you a little clinical history of these. This is the other eye of the same patient, which has essentially the same type of trifoil look. The first example I am going to put up here is a 60-year-old patient who came in for refractive surgery. The patient is close to Plano in one eye, and a little hyperopic in the other eye. You will notice that the only thing that doesn’t quite match here is the uncorrected vision of 20/30, and a best-corrected vision of 20/20 with only a 0.25 diopter sphere, and slightly less best-corrected vision in the right eye. This is OrbScan. Again, this is pachymetry down here and this is the area there. Perhaps I can start out with Ron. Ron, what do you think the wavefront is going to look like on this particular patient?

Ronald R. Krueger, MD, MSE: I’m not familiar enough with OrbScan to be able to make a lot of comments, but it looks as though there might be some spherical aberration or something there.

Dr Durrie: Because of this elevation map, this is something on OrbScan that is a slightly decentered apex. If we go back to the shape of the eye, an eye is shaped rather like the point of an egg. We find that some people don’t look through the point of their egg naturally. So if you look at this and this in that area, it ends up with a lot of coma, because they are just not looking through the center of their eye. And so you can see that in the 2D or 3D. If we go back again and look at this as that area, you can see that shifted over to the side, and then if they are looking through the side of that, they are going to end up having coma. If you put it together, here is the OrbScan and here is the coma. With Zernike polynomials, this is going to divide that up into two areas. The largest is vertical coma and then there is some horizontal coma as well. I have found that this is the best way to start separating something I already know from something I don’t, and trying to correlate those together. In general, if you have microns of deviation greater than 0.5, it is getting to the point where that is usually a large number. We are still learning about what are high numbers and what is clinically significant. But that’s the way to look at it. Steve, what is this one going to look like?

Stephen G. Slade, MD, FACS: Is that post RK?

Dr Durrie: It is a post RK patient.

Dr Slade: He would probably either have trifoil or a lot of spherical aberration with that.

Dr Durrie: What Steve is saying is spherical aberration, and you keep hearing that term, and anyone who has had refractive surgery, especially radial keratotomy, has it. Also, at the top of the OrbScan you can see bumps, and when you start looking at these as well, there is a lot of trifoil there. This is because you are seeing these bumps here. So when people look at this and try to see the dominant term,

there is trifoil here and spherical aberration as well, which is this one over here, but the dominant one ends up by being these bumps out here. The interesting thing for me is that if we just turned one of the lasers loose on this, if we just plugged in our nice custom laser, where is it going to throw all the pulses? It is going to fix this. It is going to pound right on those weak spots. And I think this is a key issue which we are going to have to look at. As we start having these machines that find problems, and say, “O.K., I’ve found it, I’ve located it, I’m going to fix it”, do we really want these lasers pounding a whole lot of pulses right in an ectatic area of the cornea? That would be like a keratoconus patient, if they have a bump out there, do we really want the laser to beat on the bump, because optically we want to make it better. That’s why I’m talking to the laser engineers a little bit. We have to be able to shut off some of this stuff. Clinically, once we learn things, we have to be able to say, “Don’t treat the trifoil in this patient”, or, “Don’t treat above third order in this patient”, because we already know that, clinically, that might be a bad thing to do. The reason this is important when working with the FDA on clinical trials in the USA, is that we have to have some interaction software, what I have been calling linkage software that goes between the aberrometer and the machine, so that we can get in there and say, “Gee, we learned this, and how do we shut that off?” Steve, what is this one going to have? This is an 11.00 diopter LASIK.

Steven Schallhorn, MD: I would say that there is a tremendous amount of spherical aberration on that eye.

Dr Durrie: Anything else?

Dr Schallhorn: Perhaps some coma.

Dr Durrie: I think the reason he is absolutely right is that you start seeing this as being flat in the center and having this ring around the edges there, and you look at the spherical aberration and this is huge, but there is also some horizontal and vertical coma, but this isn’t exactly in the center. The slightly decentered ablation is going to give you some coma in both directions and then a lot of spherical aberration. These are the patients who have a lot of problems with halos. We are starting to see a lot of correlation with that.

I think everyone is going to vote for coma, and mine is off the scale. So this is coma. And this is one thing we have been looking at, and Steve Schallhorn has found this occasionally. Vertical coma, in some patients, especially when they have had it all their lives like I have, is not so bad. As a matter of fact, I like my vertical coma because I can see up close and far away, but could you take that much coma and put it on someone else and have them be happy? I think that is the real question. Or, if you gave my eye a Plano wavefront, would I be unhappy because I had lived with it this way all my life? It is something I have in both eyes, and my daughter has it also. So it is interesting to see how that relates. Now I am going to switch gears a little. This a Nidek OPD map, and this one has topography at the top, so it is an axial and meridional topography, and then this is a map that is slightly more unique to the Nidek philosophy. This is a dioptric power map. So they have taken their technology and come up with a dioptric power map. OPD means optical path difference, and is essentially, if you look at the wavefront from

one side and at the other side mathematically, one described as a wavefront error, while the other side is described as an optifact difference. And these are the high order aberrations and these are the Zernikes down here. So this is another type of map, and this is the OPD. It shows in diopters with myopia in the hotter colors and hyperopia in the bluer colors. This is another example. Karl?

Karl G. Stonecipher, MD: Basically, what I see is a little trifoil and a circle.

Dr Durrie: So Karl also sees this red ring out here, Paolo’s famous red ring, which is a little spherical aberration in this patient. This is a 26-year-old, 10.00 postop LASIK who sees 20/20 uncorrected and really complains about halo and glare, and this has a spherical aberration, some horizontal coma also, and this trifoil. One, two, three, you can count the trifoil down here. In the dioptric map, you can see that it is more myopic out in the periphery than in the center, and essentially Plano in the center.

Raymond A. Applegate, OD, PhD: Dan, how big is that pupil?

Dr Durrie: This measurement pupil, this is at 5. One thing that Ray just brought up, which is extremely important, is that high order aberrations are radius-dependent. So one problem we have is that if one machine reports 5 mm and another 6 mm, and yet another 6.5 mm on the same eye, you are going to get totally different values. So this one is set at 5 mm at this point in time. We are trying to get the industry to all do them at 6, so that everyone does it the same and then we will be able to compare the numbers. I really have to compliment Ray Applegate and Ron Krueger tremendously for working on standards. This really is something we appreciate. I think these standards are very important. This is the other eye of the same patient. You can see that it is essentially the same, but now you can see this whole bunch of coma. And the one coma I find always to be consistently bad is horizontal coma. People hate horizontal coma. They have monocular diplopia, it affects them up close and far away, and I think it is something we really need to avoid. This is someone with severe complaints and halos. Even though they are 20/25 and used to be a -11.00. We all have these: the patient who comes in and we say, “Boy, you should be happy, you used to be a -11.00.” But they are not that happy because the quality of their optical system is not all that great.

Dr Applegate: I think it is a really important point why horizontal coma is worse than vertical coma – in horizontal coma you can’t use your eyelid to block some of the pupil. So, as you bring down your eyelid, you may be decreasing the total number of aberrations, but you still have horizontal coma, whereas in vertical coma you can choose to block. I haven’t studied you and how you manipulate your eyes, but I would bet that you use your eyelid to block off when needed.

Dr Durrie: I think that is absolutely true. We have gotten to the point in the clinic now that when someone comes in, we can almost tell them their symptoms if they have horizontal coma. It really affects their reading a lot. They almost say that they see two letters on that basis. This is a patient whose topography is slightly irregular, whose power map is a little irregular, who has coma here. What I have also found is that if you have negative vertical coma, as I do in the lower part of my

pupil, I have more power down there, you flip it upside down, people hate this too. They don’t like their coma the other way round. So that is the other symptom I have been seeing. They don’t like it this way, and the only way is to have a little myopic power down below. Steve, did you see any correlation in the direction of the coma in your Top Gun study?

Dr Schallhorn: We didn’t look at the directionality of that. We looked at the absolute value in all the regression analyses we did. So it would be interesting to go back and look at that. Intuitively, I think it makes sense.

Paolo Vinciguerra, MD: In this case, as in the others, if you see the edge of the ablation where the red ring is located, there is always a much greater difference between the nasal and the temporal area. That is because the pupil is usually displaced nasally. And then you line up your laser on the pupil. So nasally, the cornea reflects naturally, and the edge of the ablation is not as crucial in terms of curvature change. In the other direction, always yes, it is more. So you see the dioptric gradient more prominently. This creates the difference in curvature. This creates the coma.

Dr Durrie: I think that is really important, because I don’t think there is anyone who has been trying to adapt this in their laser algorithms. Because we are seeing horizontal coma postoperatively in our standard and customized patients.

Dr Vinciguerra: But look, in right eyes, you always have the displacement in aberrometry nasally and in left eyes you see nasally, which means that you can predict where your coma will be.

Dr Durrie: This is what we need to keep talking about. This is when people start having significant quality vision problems. This is constant halos. This is a patient who had LASIK. I didn’t know what the preop was, he just showed up for a second opinion. I do see patients now who have a tremendous amount of oblique coma, spherical aberration, but in the dioptric power maps, have these areas where they have five or six diopters of different power, and this is all within the pupil. This is a patient whose uncorrected vision is 20/20. Because they are essentially Plano in the center, you bring them into the office and make their pupil small and their refraction looks fine. I am really finding these instruments very valuable, because they tell me something: that these patients aren’t crazy; they are not just complaining; they really do have very significant optical problems. This, again, is my eye, looking at it on this map and looking at it showing that I do have a decentered apex. I have a naturally decentered apex. This is that whole bunch of coma, and this is the dioptric power difference. Something that kind of throws us off occasionally, although this is a patient who comes in and has absolutely no complaints at all. The vision is perfect. This is what we talked about last week in Interlaken. We find these patients and say, “Ah ha, I found it”. When you have this you have bad vision. And then someone like this comes in, and I see a lot of residual astigmatism. I see a lot of spherical aberration, everything, they have trifoil. But the patient is 20/60 and has absolutely no complaints, says their vision is perfect, and they are absolutely ecstatic, telling all their friends. This is the other

eye of this same patient and has what I would suspect to be a lot of optical problems. I quizzed her a lot, because when I looked at all this, I said, “Oh, no, this is going to be terrible”. And she even has residual refractive error. But we are still not always hitting it here.

Dr Applegate: I think these cases are very interesting, because again, if we look at this as a silver bullet, we are looking at it wrong. First of all, notice it is a tendiopter myope. That’s a lot of RMS error. So she probably reduced her RMS error by 90 percent, and if you improve somebody by 90%, they are probably going to be relatively happy. But the next part of it is that I’d like to know what her aberrations were before she had surgery, because she may have had a lot of aberrations anyway, even with glasses on, so that she has never had a high quality image. It is really the change, I think, that we are going to be looking at. I like to use the analogy, if you have someone who walks in with 20/15 or 20/10 vision and a -3.00 correction, you are probably going to make that person worse. But if that same -3.00 patient came in and they were 20/20 best-corrected, you are probably going to be just fine. I would be really nervous. I am not a refractive surgeon, but if I were, I would be nervous with the person who came in with really exquisite vision to start with.

Dr Durrie: I think you’re right, but I have also had -12.00s who look perfect and still complain. So perhaps we need to have some personality tests on this. David, is adaptive optics going to help us in some way with these diagnostic things? We are all hoping we can take this and show them something in the exam room.

David R. Williams, PhD: I think adaptive optics can play a role, not only in showing the patient what the benefits of customized refractive surgery might be, but also for the physician, because you could actually, in this instrument, endow the physician with a wave aberration of the patient’s eye. So, if you want to diagnose some of these problems and understand what the patient is really talking about, and translate the verbal description of what they are seeing into a firsthand impression of what their wave aberration is like, you can actually create in the physician exactly the same wave aberration that the patient would have. And I think that could be a very helpful tool.

Dr Schallhorn: The other thing, too, is that adaptic optics would be useful in cases like this where you could correct those aberrations that you see and then find out if the vision was truly better, because as Ray was saying, she has always lived with these aberrations. I think adaptive optics would be an incredibly useful tool.

Dr Durrie: I told Ray last night after a few glasses of wine that what I really wanted from all the engineers and people here is in my folding lane to have adaptic optics on the second mirror and a little knob there, and how much do you want to pay me? They told me that is still a long way off.

Dr Stonecipher: Dan, along those lines, I would like to make one comment. Obviously, we have a lot of these people in our practice who are not doing well, and we want to make them better. But along the same lines, what I think wavefront technology is doing for us too, is to make us better refractionists. It is making us

think about the refraction, so in RK days, I was looking back and we had ten technicians who did all my refractions. I looked at that and they were all doing them at different vertex distances in different rooms, and it mattered whether they were -1.00 or -7.00, like Ray has been talking about, and we finally went on to a different system where I only used two rooms and two technicians, and that tightened my results a great deal. We are still trying to decide whether we are going to operate on it at 4, 5 or 6 mm, and what’s real, and how do they match up, and do we do someone who is half a diopter different than their wavefront, or what we do. But I think that, if it’s going to help us on one thing, it is going to help us decide who not to operate on, which is what you are alluding to, and help us choose the right number.

Dr Applegate: I’d like to hear David’s comment on this. I am a believer in your visual system getting very used to whatever you have. As we all know, if we rotate a cylinder axis, or if someone comes in and has a three-diopter cylinder, and we’re going to do it for the first time, we probably won’t correct the full cylinder, we won’t rotate an axis of a large cylinder very far even though we know it’s off, because the visual system has adapted to it. We all know that you can slowly move the person to the optimal correction. So, I am wondering about the lag time, whether you could actually sit someone down in an office, as you were saying, which do you want, one, two, three, four. While you can clearly see improvement, it is my guess that the true improvement won’t come out for several months. I’d like to hear David’s comment on this.

Dr Williams: We don’t know how long it will take for that adaptation process to occur. I do know that, in experiments in my laboratory using laser interferometry where you can bypass the optical blurring in the eye, patients would routinely be unable to see very high spatial frequency, very fine gratings projected on the retina with interferometry initially, but then after several days, and it would typically take several days for them to learn to be able to see these patterns, the contrast sensitivity would systematically rise over that period. But we don’t really have a firm estimate of the time constant on that. There is a learning effect, but one factor that mitigates against the importance of that a little is that, while people have aberrations that they have lived with their entire lives, their view of the world is actually determined by more than just those aberrations. What I mean by that is, that they know what a sharp contour looks like because they sometimes view those contours close up when the object that you’re looking at is magnified. They sometimes also view them with smaller pupils, when these aberrations are less prominent. So they have internalized in their nervous systems the concept of what sharp contours are. And that tends to mitigate a little against this notion that you get accustomed to your wave aberration and you won’t like anything that is better than that. With our adaptive optic system, we find that people always prefer fewer aberrations when given the opportunity to view things that way.

Dr Durrie: This kind of goes both ways. We certainly know this from Kevin Walsh’s talk on people adjusting to rays, halo, and glare over a period of time. People adjust to that. They adjust to monovision over a period of time. There are all these factors that overlay this. This is another example, and it was an interesting case. This patient has 20/200 best-corrected vision, and the Retinal Service sent him over

and said, “We can’t find anything wrong with the retina. Is there something going on in the cornea?” The patient’s refraction was -6.50 -3.00 at 090, and I was simply able to do an aberrometry reading and say, “The optical system looks fine. I find all that error and everything there. I don’t find anything unusual.” The quality of all the systems looked good. So I could send him back and say, “Keep looking, it’s not on the cornea”. So I think there are other things we can look at. We can look at the quality of the optical system. This is a preop, and again, I am going back to an OrbScan. This is one of those things that comes in every once in a while where you have no data, with something funny next to it, saying, here’s a no data area and this looks like a red spot. Is this keratoconus or not. And you look over and say, “Well, there’s no thin area in the cornea there. Is this just a decentered apex?” This is the other eye, and this is the classic asymmetric astigmatism we are always seeing on a Placido disc. How did this work out on this kind of system? Yes, it correlates very well. Here is the topography with that patient, and yes, there is that inferior spot that looks like something to worry about. Obviously it wasn’t just missing data because it showed up on multiple machines, but also, it is pretty obvious on the dioptric power map that there is a much higher power here, and also here is the vertical coma that you would expect. These facts are still not telling us whether we should operate on these patients or not. That is one of the questions. Should we let the laser pound this spot, which is what it would do if we let it go on its own. If you look back here, this doesn’t really look like a keratoconus, because it is not thin. It just looks like a decentered apex. These are the ones I want to try, with good informed consent and saying, “Let’s let the laser correct these patients because they correct the coma, get rid of some of that”, but we are going to have to say, “We don’t know whether this is keratoconus or not, because there are a lot of these around”. And I think that this is one of the things we will need to look at. So basically, I think we are still going to have to have topography. And we know that that’s necessary. I think we are going to take the elevation maps and look at the shape of the eye, but these new devices have opened up my eyes to the importance of refraction. Where are the light rays when they go through this person’s pupil? That’s really what we’re asking. Where does everything go to as we shoot it through the eye and it goes through the pupil, and how does that relate to the symptoms the patients have now? And we’re starting to think that perhaps this is something that can explain their glasses symptoms. Perhaps they should get customized contact lenses. Perhaps they need a customized implant. So I am not just looking at running a laser, I think we are really looking at this as something from which we can all benefit.

Any general comments here – anything you feel the audience should know from what you’ve learned about how this helps you in the clinic? What are the pearls out there?

Dr Applegate: I think you’ve been alluding to it, but not saying it outright, and that is that by combining topography in a wavefront measurement, you can look at the source of the error. Wavefront measurements by themselves don’t tell you where the error occurred, but if you combine them with topography measurements, you can sort out where the error actually occurred. And I can give you some intuitive feeling for it. I think that, if we went over the slides again, we could almost talk at them that way. The cornea is about 70 to 75% of the optics, and so you are going to suspect that. So corneal topography has to play a role. But sometimes corneal

topography doesn’t reveal this, but the wavefront map will. At that point, you now know and have to suspect the lens inside the eye or some other refracting surface. So, this will allow you really to tease out the source, not only to identify the source, but also to tease out the location, and then design therapy accordingly. I think that is a very powerful tool, and we will simply continue to refine it over the next few years.

Dr Durrie: Ron has a couple of cases here he was going to show while we are going down the line. Steve?

Dr Slade: Just to back up Ray’s comment, the clinical topography is certainly important, since we are operating on the cornea. The other thing I have found useful, since I have had a couple of them, is the point spread dot, the PSF diagrams, to show a patient. Psychologically, the patient will present with a problem. If you can just show them one of these nice point spread functions, it is what they would visualize if they were looking at a distant point of light, and there is this eureka moment for a lot of them. They will say, “That’s exactly what I see”. Even though we can’t fix it, it’s comforting for them to know that we can diagnose it and quantify it to that extent. They think we can fix it now. So that helps a lot of these people to calm down and be a little happier.

Dr Krueger: I didn’t know whether we were going to bring cases or not, so I just had one prepared and I thought it might be useful just to mention it really quickly. One of the ways this is helpful is when problem patients come into your office for whatever reason, whether it is one of your own or from someone else, to give you additional information that will help you make a decision on their behalf. So here is someone whom I think is pretty frustrated. He has blur symptoms, diplopia, glare, halos. He is nine months after surgery. He doesn’t seem to be getting any answers from his surgeon. He is 31 years old, an otherwise healthy guy, who wants to come in knowing if he can have custom ablation because he has heard something about it. Here is some of his information. He is about 20/50 in his right eye with +1.00 -1.00 refraction. It is kind of close to ametropia, but he only corrects to 20/40, and when I looked at the wavefront refraction, it showed a great deal of cylinder in his eye. This kind of shows that. What is really curious about this case is that you can see a large blue spot down here below, which represents a localized area of myopia. At least with the Ladarwave that I use, I can look at the twodimensional map and I can also expand it into a three-dimensional one. Interestingly enough, here you can see he has this huge amount of trefoil, and his other terms value is about three microns, or something along those lines, so it is really quite high. So I am looking at it in different shapes, but you can see that tremendous dip right there, and he basically has ectasia. It shows up slightly more inferiorly. He is not going to benefit from having any further refractive surgery and he has a lot of aberrations to deal with. So I basically told him, “Don’t pursue any more surgery right now,” and this was a problem for him. So this gives us some additional information. The topography already hinted at that, but at least from his perspective, it was nice to have a wavefront just to supply some additional information and provide him with an answer.