Conductive keratoplasty using radiofrequency energy to treat hyperopia

Daniel S. Durrie

Hunkeler Eye Centers, Overland Park, KS, USA

I am going to talk about something that is available here, since it recently received FDA approval status. I am talking about the conductive keratoplasty system. Many of you will have seen it, but I think it is a tool that you will pretty soon be deciding whether or not you are going to add to your other instruments. It involves a little tip that passes radiofrequency waves that can shrink the cornea. This can definitely be done at the slit lamp: you just go around, follow the dots, and push the pedal. It is a very simple procedure. Patients do not seem to be bothered by it much, and it is quite easy to perform. The way it works is that it causes shrinkage of the collagen here to form this belt-like area around the cornea in order to steepen the center. This is not a new idea. We have been doing it with surface holmiums and with the sunrise LTK, but what is different about it that could potentially make it better, is the depth of the coagulation spot. It is deeper. And deeper has been shown in all the studies to be necessary for stability. All you have to do is to look at the stability curve of CK over 12 months and you can see that there was a little bit of myopic induction and a little bit of regression over a period of time. At one week, my LTK patients were all the way over to a –2.00 when I was shooting for Plano, whereas these people were –0.75 and happy. That’s the big difference. We performed ultrasound on this and it showed that these are definitely back in the posterior area of the cornea, whereas we saw that the LTK spots were not only superficial, but also there almost seemed to be a break in Bowman’s anteriorly with these.

I looked at the data that Marguerite reported at the FDA. It was a large series of patients, a typical US clinical trial, with excellent accountability and 97% of the patients being followed, 401 eyes, and these parameters basically, with no nomogram adjustments after the first: we did 50 eyes, changed, and then it all stayed the same. Fifty percent 20/20, 91% 20/40, beat the FDA guidelines. When we look at our myopic results, all excimer lasers are much better, but if you look at the excimer laser results for hyperopic LASIK, having 50% is fairly competitive out there. I think this could be even better once we fine-tune things. The accuracy was good out of the blocks. Even looking at 12 months, there was not a lot of regression. It’s not as if all these cases started off over-corrected and then went over here. There was a little bit of regression, but not much. Again here, these curves in manifest and cycloplegic refraction. Also,

Address for correspondence: Daniel S. Durrie, MD, Hunkeler Eye Centers, 5520 College Boulevard, Overland Park, KS 66211, USA

Wavefront and Emerging Refractive Technologies, pp. 65–66

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

the stability, and these are new data you probably have not yet seen. This is a 24-month study which really shows there is about 0.25 diopter a year regression in these patients, which has been very acceptable to them. What I am really interested in is using this for monovision and presbyopia. We have carried out an FDA study on this. As you would expect, the safety data were excellent in this small group. There were five of these patients whose distance vision we also wanted to correct, so we did CK with a little bit of a nomogram adjustment from what we originally did. They were 100% 20/20, which were obviously good numbers, and 100% within a half diopter. Also, the ability to read up close was quite good in these patients. We just did one eye, monovision, and only shot for a –1.00, and these patients were still reading J2, a high percentage in J3, no induction of dry eyes, did not experience much discomfort. So this is very competitive for the near vision. Plus, their binocular uncorrected distance vision continued to be very good, because they just had a small amount of monovision. Very accurate, 88% with ± one half, only one patient over-corrected, one patient under-corrected. Stability was good early. We shot for a –1.00, and essentially got a –1.00. We did have some induced cylinder, but this is something that I think is easily diagnosed and can be taken care of. If we look at what we are really doing, we are operating in the periphery, and the corneas are different thicknesses in different patients and have different curvature, so as you steepen it, patients sometimes need an extra spot out here. This is quite easy and you can do it at the slit lamp. The quality of vision has been excellent. And the contrast sensitivity measurements from our clinical trials are good too. In contrast sensitivity, you count patches and then see whether it changes preand postop. The data showing without glare and with glare is the only clinical study I have ever done that actually had an increase in contrast sensitivity throughout the study. That showed up in our whole group, which is very interesting, and also correlated to a very high patient satisfaction in this group. Again, you have to compare apples to apples. I have done a lot of clinical trials. We have a percentage of patients who always say they did not get better, no matter what. It is usually higher than this. I do not usually have this much extreme or marked improvement. You can look at these numbers. If you add these two together, we are looking at 75% of these patients who were in a clinical trial and who are saying that they had a markedly extreme improvement in their quality of vision. This was the quality question. Overall satisfaction was very high. We did focus groups on this afterwards. So people are really looking at this as an alternative for some of the other things out there. In my practice, I have been looking at the topographies and at the quality of vision, and no dry eyes. For the low hyperopic patient, this is a very attractive alternative to hyperopic LASIK – less expensive, doesn’t remove any cornea, not in the optical zone, doesn’t cause dry eyes, good quality vision. It lines up with a lot of those things, so I think it is worth looking at. As we know, a lot of things look good in clinical trials, but do not look so good in the real world. So we have to test these things. This is something we are going to have to look at. I think that this is very promising for inducing monovision, very promising for hyperopia.

The other thing that I think is going to be really neat to look at is, can we correct astigmatism with this. I do not mean just for someone in refractive surgery, but imagine someone who was having difficulty with a toric soft lens, and you went at the slit lamp, put in a couple of dots, and now they can wear a spherical contact lens. A postoperative cataract patient who has one diopter of astigmatism, at the slit lamp you put a dot in, and now they do not have astigmatism any more. Why would you do a corneal relaxing incision if you could strengthen it 90° away if it continues to work the way we want to see it? It would be fun getting this out on the market and finding out what its real value would be for us.