Round table: Safety of advanced surface ablation techniques draws interest

OSN convened a panel of refractive surgeons to discuss the recent resurgence of interest in surface ablation. Reasons include advantages in safety, reduction of dry eye, and advances in pain management.

Ocular Surgery News convened this round table of refractive surgery experts to discuss advanced surface ablation during the ASCRS Summer Refractive Congress in Seattle.

Seattle — Richard L. Lindstrom, MD: Recently we have seen a resurgence of interest in surface ablation. Some people call it advanced surface ablation. What does that mean to you? What is different about what we do today versus what we did when we first got started?

Marguerite B. McDonald, MD: I think advanced surface ablation is anything other than the original PRK that we did some years ago. So advanced surface ablation really includes laser epithelial keratomileusis or LASEK, alcohol-assisted LASEK and epi-LASIK.

Richard L. Lindstrom, Moderator

Dr. Lindstrom: In what ways are these techniques an advance over what we did previously?

Dr. McDonald: These techniques are an attempt to save the sheets of living epithelial cells that are either mostly living, or at least partially living, so that they can be redeposited on the freshly ablated surface.

Dr. Lindstrom: What science is there to support the concept of retaining and replacing the epithelial flap?

Dimitri T. Azar, MD: If we are able to obtain epithelial sheets that are viable, that have their own basement membrane; that eliminate the pain; that does not go too far into Bowman’s layer; and minimizes the scarring and the haze that can occur afterward, then clearly we will end up with a procedure that is superior to LASIK and PRK in every respect. But this is all a theory.

Pain is an issue because most surgeons use only a low concentration of anesthetic postoperatively, together with applying cold saline or balanced salt solution during the surgery, and some surgeons also use steroids. In regard to the speed of healing, we are not sure whether there is really an advantage of leaving the cells in place and waiting for the other cells to replace them. You have a sheet of cells that will be ultimately replaced by other cells, and you compare the speed of closure or replacement of these cells to an area where you have full debridement, as in PRK. The speed of closure is not going to be greater when you have PRK than when you have cells standing in your way. Again, this is all theory.

Dimitri T. Azar

Regarding the issue of haze, several studies have shown that perhaps there is less scarring and less deposition of type 3 collagen in the stroma after LASEK than after PRK.

Why the return to PRK?

Dr. Lindstrom: About 12 years ago, we were doing almost 100% PRK. Around 1994, the transition started to take place to 100% LASIK, and the transition occurred rapidly. In 1995, PRK was approved, but at that point most of us were not using it anymore or had already gone on to LASIK. Now in 2005, we have some surgeons doing all PRK again. What is wrong with LASIK? Why are we going back to surface ablation? What have we learned that we did not know 10 years ago about LASIK that has caused us to re-evaluate?

Helen K. Wu, MD: I think the biggest concern is safety. When you see a number of patients showing up at your doorstep with LASIK-induced ectasia, then you start to take a step backwards and say, “Do we need to be cutting flaps in corneas and doing ablations deeper and further?” So I think that is the No. 1 thing.

Helen K. Wu

I think that is also true because of the switch to custom ablation because you need to take away more tissue. If you are doing deeper ablations, you have less room to do LASIK, so some of those patients that were borderline for conventional LASIK, if they want custom we may have to go to surface ablation because they do not have enough cornea to do it.

With improved pain management and improved epithelium management, surface ablation is not as big an inconvenience for these patients, and they are able to get through it. Although it is a little uncomfortable, it is not a bad experience for them. So I think those are reasons why people are going back to it.

William B. Trattler, MD: There are patients who appear to be perfectly normal candidates for LASIK who can end up with ectasia. I think that is one of the reasons I switched, and I switched to 100% surface ablation about 3.5 years ago. However, I also switched because the quality of vision with surface ablation has improved over the past number of years because of improved laser technology.

Ronald R. Krueger

Ronald R. Krueger, MD: I would approach this from a different route and say that the real resurgence for me was that we discovered what aberrations were, and we began talking about “super vision.” In the quest for super vision, we found that there was a lot of evidence to suggest that by being on the surface you may actually get fewer aberrations, and we were looking for how to make custom ablation better.

Advances

Dr. Lindstrom: Let us discuss the advances and changes in surface ablation over what we were doing in the 1990s.

Dr. Trattler: Right. Why do I have patients who now want to have a surgery that has been available for 10 years? The patients who said they have waited said they were waiting because they wanted a procedure that has less risk than LASIK but still has excellent visual results.

Dr. Lindstrom: So we have moved to a new patient population?

Dr. Trattler: I definitely have seen that.

William B. Trattler

Dr. Lindstrom: In my practices we are seeing a trend toward younger patients and lower myopes.

Dr. Azar: We have all now seen our PRK patients 15 years later, and they are doing fine. Their past visit may have been 9 or more years ago, and they left you then with excellent visual results.

Dr. Lindstrom: And now you cannot even tell they had the treatment.

Dr. Azar: Ten years ago the scarring or haze rate was higher because many patients with higher refractive errors were being done without adjunctive application of mitomycin. Also, maybe the lasers were not as sophisticated as they are now.

Dr. Wu: And the optical zones were smaller.

Dr. Azar: And we were going deeper. About 2% of patients had scarring. But if you look at the remaining 98% that are doing well, we do not see long-term complications. We cannot reassure a patient who is asking today what will happen 15 years from now after LASIK surgery; we cannot give them the same level of reassurance that we can regarding surface ablation.

Dr. Lindstrom: We have a somewhat different patient population, a more risk-adverse patient population than we had 10 years ago.

Dr. Wu: I think they are more educated too. They read about the complications, they go to those Web sites, they read some of the literature, they know the terminology, and they understand more.

Dr. Krueger: I would say that our biggest concern among LASIK patients is stability, and what happens to the cornea long term. We know that there are studies from Jose Barraquer going back 50 years saying that if we adhere to certain parameters, and the patient does not have an unhealthy cornea, the cornea should be OK. So that is what I tell patients when they ask me questions about long-term safety with LASIK vs. PRK.

Candidates

Dr. Lindstrom: Who definitely should have surface ablation rather than LASIK or something else?

Dr. Trattler: I think patients with thin corneas should have surface ablation. When you talk to LASIK surgeons they may have different numbers. Some say the cornea should be 500 µm, some say 490 µm or 480 µm, some go even lower, but certainly with a thin cornea there is a concern that there might be an increased risk of ectasia with LASIK.

Dr. Wu: I get extremely nervous if I see against-the-rule astigmatism in anybody who is young. I look at the posterior slope of the cornea too, and if I see a symmetric bow-tie astigmatism with anterior steepening, and I see a posterior slope that is greater than 40 D, then I do not do anything to them, because I think their cornea is actually somewhere on the way to keratoconus.

If they just have an anterior surface abnormality, then I caution them. I tell them to have surface ablation only. And if they have both posterior and anterior abnormalities I do nothing.

Dr. Azar: We came up with a decimal score. There are 10 different criteria, and if patients were diagnosed with a suspect or keratoconus, they would get one or two points, and we added then the scores from 0 to 9. So with a score of 0 we could do LASIK. If we get anything between 1 and 3 it is OK to do PRK, and anything 4 or above, which means we are talking about early or advanced keratoconus, then they get no surgery.

Marguerite B. McDonald

Dr. McDonald: Even for surface ablation I have a high threshold for canceling. We also started studying the topography much more carefully. I rely on some of these programs that have been designed to help doctors with patients who might have keratoconus, for example, which many of the manufacturers have. I do not operate on anybody with a central thickness under 500 µm. If it is under 500 µm, they might not even get a PRK.

Dr. Krueger: But that is a hard statement to say because even if you look at what is the average corneal thickness in a population, only one standard deviation or so below the mean gets us to 500 µm, which means there are a lot of normal eyes at or below 500 µm.

Dr. McDonald: So 500 µm yes, but below 500 µm, if they get in to even 490 µm I get nervous. Now, admittedly, I probably have lost a few cases, but I would rather know that I let a few good candidates slip through my fingers than the reverse. We also measure the midperipheral cornea, and the periphery should be at least 20% thicker than the center.

Dr. Krueger: If we were to really break it down concerning post-LASIK ectasia, we are most concerned about topographic shape, thickness and age. Maybe elasticity should be in there too, but we have no way of measuring that yet.

Dr. Lindstrom: I think shape matters.

Dr. Krueger: Yes, shape matters, based on what we see on the topography, but an irregular shape is a late manifestation of abnormal corneal elasticity.

Dr. Wu: Yes, for me, also, it is the shape. In fact, if there is any hint of inferior steepening I just do not do it.

Dr. Lindstrom: The ones that seem to be getting people into trouble are the asymmetric bow ties that occur in 14% to 15% of the population.

Dr. Trattler: The key here is that you must give these patients proper informed consent. You identify the issues, you explain that their topography has an abnormality, for example, and go through what that might mean if they proceed with a particular type of surgery. If you properly identify the abnormality and explain to them the risks and benefits of each procedure, the patient can decide based on their risk tolerance.

Dry eye an issue

Dr. Lindstrom: There are many surgeons doing LASIK on patients that have at least mild dry eye symptoms. When a 35- to 40-year-old patient with myopia comes into your office and says he has become contact lens intolerant, maybe he is taking lubricating drops a few times a day, what do you do?

Dr. Wu: If they have lissamine green staining of their corneas, then I do not do anything until I improve that. If they have a Schirmer’s test score of 0 or if they have keratoconjunctivitis sicca with Sjogren’s syndrome, I will not do anything but surface ablation.

Dr. Krueger: I look at three main things: symptoms, staining and results of the Schirmer’s test. If it looks like a person has all three, I will go in the direction of PRK. If it looks like they have one or two of them, I will try to optimize them — in other words, I will put plugs in, or I will give them tears — and then ultimately do LASIK.

Dr. Azar: I do something similar. We try to do Schirmer’s on as many patients as we can, but in a questionnaire we ask whether patients have symptoms of dry eye. Of all the predictors of dry eye disease in large population studies, we think the best way of knowing somebody has dry eye is to ask, “Do your eyes feel dry, and have you had difficultly wearing contact lenses because of dryness?”

You have to tell the patient that if we do LASIK there is a greater risk of having an exaggeration of these symptoms after the surgery, and that may persist for as long as 6 months and perhaps longer. So the patients have to be prepared for 6 months of worsening of their symptoms, and that makes the patient hesitate to have LASIK.

Sometimes patients ask me whether there are reports to prove that PRK has less worsening of dry eye disease than LASIK. I tell them I am not aware of any, but at least in theory it makes more sense because the LASIK dry eye is related to the regeneration of the nerves, and we know that nerve regeneration is extensive, and they are left more complete after PRK than after LASIK.

Dr. Trattler: Compared to LASIK we have less overall dry eye with surface ablation, but I do have some patients who have undergone surface ablation and later developed significant dry eye. These patients can be a challenge to treat.

Pain management

Dr. Lindstrom: Nobody likes pain. I used to always say it is a no-brainer for patients to choose LASIK over PRK, as they see well faster and there is almost no pain. But with surface ablation we obviously have pain. What is your pain regimen?

Dr. Trattler: I think one of the keys to avoid pain is to identify patients with dry eye preoperatively. When one of my colleagues performed surface ablation on a few patients but did not question these patients carefully about their dry eye symptoms preoperatively, they ended up with increased postoperative pain along with a delay in epithelial healing. So I try to identify patients with dry eyes preoperatively and pretreat them with Restasis (cyclosporine, Allergan) and punctal plugs.

I think another critical aspect is picking the right contact lens. Right now I am using a lens called the Acuvue Oasys (Vistakon), which is a new fourth-generation soft contact lens. It is more oxygen permeable and more comfortable for patients. We have been using this contact lens over the past few months, and we have found our patients have less pain postoperatively.

I am also using both Acular LS (ketorolac tromethamine, Allergan) and Xibrom (bromfenac ophthalmic solution, Ista Pharmaceuticals) for topical pain control, and these medications have been helpful.

Dr. Lindstrom: What else do you find useful?

Dr. Wu: I was using a Demerol (meperidine HCl, Winthrop) combination in the early PRK days, and then we used Mepergan (meperidine/promethazine, Wyeth). That went off the market, so we used Percocet (oxycodone, acetaminophen, Endo Pharmaceuticals) for a while, and we found that patients were not tolerating that as well, so we went back to writing two prescriptions for Demerol and promethazine, and I think that works much better. We use preservative-free Acular every 4 hours and we give them tetracaine every 4 hours. We tell them to use it every 4 hours, and then we take it away from them after the first day.

Because we use chilled saline before and after, the pain for my patients is different now. It used to be that they peaked in the first night, in the first 24 hours, and now they peak on the second and third days. Now they do not have pain on the first day. On the second day, usually when they wake up in the morning and the sun hits their eyes, that is when they start to have the pain, and then it peaks the next 2 days, and it is gone by the third day for my patients.

I think it is the chilled saline that is delaying the pain. I also ask them to use preservative-free tears like Refresh Plus (Allergan) because they are a little bit more viscous, and I have them put it in the refrigerator and use them every half-hour to an hour. We also tell them to get ice packs from the pharmacy that are dry, and put those cold ice packs over their eyes, but not to get any water in their eyes.

There are some people who say they have an 8 or 9 out of 10 on the pain scale. Most of them are at most in the 5 or 6 range.

Dr. Lindstrom: Any other additions for pain management that you have found useful?

Dr. Krueger: I am using Percocet. I give it to all my patients and say, “If you really have bad pain you can take one tablet every 4 to 6 hours to get rid of the pain.” I am not giving topical anesthetic drops. I think it may be a good idea, I just have not gone that route. I use chilled balanced salt solution immediately after the laser ablation and that has tended to help minimize pain and inflammation from tissue heating.

Dr. Azar: I use the chilled balanced salt solution.

Dr. Lindstrom: What kind of pain medication?

Dr. Azar: I give them Percocet, but more than half the patients do not need it.

Dr. McDonald: In the beginning all my patients were checking 10 on the scale for pain. When I returned to surface ablation after many years of absence, the most important thing was the huge breakthrough in pain control from the use of oral steroids. I am not afraid of using these drugs because I use them all the time for my transplant patients, and these are young, healthy people. Unless they have had previous complications from steroids, I give them steroids.

The only reason I do not give them ointment for first day is that it will clog their contacts so that they cannot see anything, and they will be very unhappy.

For Your Information:

• Richard L. Lindstrom, MD, is the Chief Medical Editor of Ocular Surgery News. He is in private practice at Minnesota Eye Consultants, 710 E. 24th St., Suite 106, Minneapolis, MN 55404-3810; 612-813-3600; fax: 612-813-3660; e-mail: rllindstrom@mneye.com.
• Dimitri T. Azar, MD, can be reached at the Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114; 617-573-4326; fax: 617-573-4484; e-mail: azard@vision.eri.harvard.edu.
• Ronald R. Krueger, MD, can be reached at the Cleveland Clinic Foundation, 9500 Euclid Ave., Room i32, Cleveland, OH 44195; 216-444-8158; fax: 216-445-8475; e-mail: Krueger@ccf.org.
• Marguerite B. McDonald, MD, FACS, can be reached at 2820 Napoleon Ave., Suite 750, New Orleans, LA 70115; 504-896-1240; fax: 504-896-1251; e-mail: margueritemcdmd@aol.com.
• William B. Trattler, MD, can be reached at 8940 N. Kendall Drive, #400, Miami, FL 33176; 305-598-2020; fax: 305-274-0426; e-mail: wtrattler@gmail.com.
• Helen K. Wu, MD, can be reached at 34 Priscilla St., Chestnut Hill, MA 02167-3966; fax; 617-636-4866; e-mail: hwu@tufts-nemc.org.