CK, LTK, or LASIK: Which Will You Use to Treat Hyperopia?
Conductive keratoplasty (CK) is a form of laserless correction that applies controlled-release radiofrequency energy within the stroma to induce collagen shrinkage. Currently under active review for approval in the United States, the procedure is performed using the ViewPointTM CK System from Refractec, Inc. (Irvine, CA). According to Lauren Kanner, Vice President of Marketing at Refractec, the treatment is applied using a 90 mm wide x 450 mm-long tip that remains cool as it directs the energy into the cornea. A footprint of 150 mm wide x 500 mm deep is created within the cornea, at a stromal depth of 80%. The KeratoplastTM tip heats the collagen fibrils to 65oC, which researchers consider to be, and what Refractec terms, the “optimal permanent shrinkage temperature for denaturation.”
According to Marguerite McDonald, MD, of the Southern Vision Institute in New Orleans, LA, CK improves upon earlier technologies by uniformly heating the cornea to a controlled temperature. “There's a consistent heating of the entire cylinder of tissue to 65oC, which is enough to change the shape of the helix, but not enough to cause necrosis,” says Dr. McDonald, who is also the system's lead clinical investigator.
With this new method for inducing collagen shrinkage, CK takes aim at the two other primary hyperopic treatments, laser thermal keratoplasty (LTK) and hyperopic LASIK. Researchers for CK say that the procedure will be a strong competitor in the elective hyperopic surgical marketplace, but other surgeons believe that CK's narrow treatment range and capacity for inducing irregular astigmatism will prove impractical in the face of alternative procedures. Here is a look at each procedure's capability in performance and application to allow refractive surgeons to judge for themselves what treatments might survive in the hyperopic landscape of surgical procedures.
Safety
The issue of safety with LASIK has gained media attention lately with recent reports of dislodged flaps and other postoperative complications. Even so, hyperopic LASIK continues to show good results in studies. One recent study performed by Arturo Chayet, MD, of the Codet Eye Institute in Tijuana, Mexico, didn't produce any significant loss of best-corrected visual acuity (BCVA). Out of 222 eyes, only three lost two lines of BCVA, and only one eye lost more than two lines from 3 to 6 months postoperatively. The study looked at predictability, safety, and efficacy in treating spherical hyperopia, hyperopic astigmatism, and mixed astigmatism.1
In comparison, LTK also enjoys a good reputation for safety. Peter G. Kansas, MD, of the Kansas Eye Surgery Associates in Albany, NY says, “LTK is a very safe procedure.” Sandra C. Belmont, MD, of New York, NY, agrees, adding that the reason is because LTK is a no-touch procedure. “It's so safe,” she says, “that this was the first procedure in which the FDA allowed us to treat both eyes while we were going through the protocol, because there wasn't any safety issue at all.”
Researchers studying the effects of CK are impressed with the procedure's low rate of risk. Robert Maloney, MD, of the Maloney Vision Institute in Los Angeles, CA, states that the efficacy of CK is on par with LASIK. “Accuracy and stability are about the same as LASIK,” he says, “and we're hopeful that the safety is better than LASIK.” One-year results of a multicenter clinical trial show 55% of 390 eyes undergoing CK had 20/20 BCVA or better, and 76% had 20/25 BCVA or better. The refraction appeared to stabilize in 6 months, with 55% within 0.50 D of intended correction, and 91% within 1.00 D.2 Dr. Maloney notes that CK spares the visual axis, a fact that he feels makes the procedure safer than LASIK.
Complications
Dry eye, flaps, and induced regular and irregular astigmatism continue to be some of the most common problems associated with refractive procedures, and each procedure discussed here offers different benefits and drawbacks in regard to complications.
Flaps. The major advantage that both CK and LTK have over LASIK is that neither of the two procedures requires a flap. In regards to CK, Dr. McDonald says, “You do not have to worry about making a bad flap, or having flap wrinkles or dislocated flaps.” She also notes that flaps tend to do poorly in dry eyes.
Dr. Kansas finds the absence of a flap an appealing part of the LTK procedure as well. “With LTK,” he says, “there's no actual cutting, so there's no chance for that type of healing complication to be a problem. It decreases the chances of surgical complications.” Dr. Belmont feels that the absence of a flap might make LTK an attractive procedure to surgeons who are reluctant to become certified in LASIK. “Surgeons who don't want to go through LASIK training will love this procedure,” she says, “because they won't have the learning curve of making a flap, and of course, the potential complications of flaps with buttonholes, less-than-perfect flaps, and striae in the flap.” She adds that LTK is also preferable for patients who are fearful of an incision and the idea of a flap.
Dry eye. The dry eye problems associated with flaps in patients over 40 don't exist with CK or LTK. “The average patient who wants hyperopic correction is 55, which means that they've already lost a good portion of their tear film,” says Dr. McDonald. “So to not have to worry so much about dry eyes and the impact on outcomes is a big thing for hyperopes.” Dr. Maloney also points out that CK doesn't seem to cause dry eye in middle-aged women, which he says is a very common side effect with LASIK.
Astigmatism. One of the most worrisome problems with the CK technology is the potential for inducing irregular astigmatism, as John Doane, MD, reminds us, “Any refractive procedure could potentially induce regular or irregular astigmatism.” LTK has not had this problem to the same degree that CK has, according to Dr. Belmont. “There is some astigmatism that can be found with LTK techniques,” she says, “but from my experience, it's rare and it's temporary.” Dr. Belmont feels that the technique of inserting the probe into the cornea is what induces astigmatism in the CK procedure. “Each spot that's placed on the cornea changes the shape of the cornea in a way that you can't really predict. But we can't really determine the effects of this until we have some long-term studies of the patients' visual acuity outcomes.” In contrast, Dr. McDonald believes that the inducement of astigmatism with CK is more a problem of surgical technique than procedure technique. “It is a procedure that's done by hand, and unless you're really careful about marking the center of the eye and delivering the spots, you can induce some astigmatism. Now, if you're the least bit careful, you won't. That's probably the only drawback, but it's one that can be safely and adequately addressed if you just pay attention.”
Dr. Kansas says that when induced astigmatism occurs in LTK, it's usually in the range of 0.75 to 1.5 D. “It's a little bit mysterious to everybody, but the thoughts are that it may be due to the unequal drying of the corneal surface while the patient is receiving preoperative anesthetic drops. It goes away, but in the meantime it disturbs the visual acuity.”
Postop complications. According to Dr. Kansas, LTK is less problematic for patients postoperatively than LASIK. “With LASIK, one has to be protective, and there are certain restrictions for the first few hours. In the first couple of weeks the patient has to be extra careful, and then down the road certain things can happen; a water-skier can fall and dislodge a flap, for example. An LTK patient isn't susceptible to any of those things. Athletes in severe contact sports won't be prone to some of the problems that LASIK patients will be.”
Night vision. While some LASIK patients report problems with seeing halos at night, Dr. McDonald has not found this same problem with CK. “We have not had any night vision problems, at least not any statistically significant number, because CK patients have their treatment spots so far out in the periphery. The central zone is huge for them.” Dr. Belmont says that LTK patients don't experience this problem as much as LASIK patients do because LTK leaves a larger optical zone. “The 6 mm optical zone of LTK is larger than the 5 or 5.5 mm optical zone with LASIK, so the situation with the glare at nighttime is decreased.”
Quality of Vision
While most physicians still feel that hyperopic LASIK is generally a safe and effective procedure, there are issues with quality of vision that are tarnishing the procedure's reputation. A study by David R. Hardten, MD, of the Minnesota Eye Surgery Center in Minneapolis, MN, concludes that while the procedure is approved for up to 6 D of correction, surgical success and patient satisfaction begin to lessen with over 4 D of correction.3
Investigators are not hearing the same complaints from patients about the results of the CK procedure that surgeons have had with LASIK. “CK seems to preserve the quality of vision better than hyperopic LASIK,” says Dr. Maloney. “We have patients after hyperopic LASIK who have 20/20 vision, but who are very unhappy with their quality of vision; they describe it as filmy or hazy, and with our present technology, there's nothing we can do about that. With CK I didn't have any patients with those complaints.”
In comparing CK to LTK, Dr. Belmont has reservations about the quality of the CK procedure, although she's waiting to see the procedure's visual acuity outcomes. “We feel that LTK is faster and will have less chance of causing any irregularities in the shape of the cornea.” However, Dr. McDonald says that CK compares favorably to LTK. “It's very deep, it's not a shallow treatment,” she says, “which helps with its effect.”
Regression
Regression has become another important topic with refractive surgery, especially when discussing LTK. Doctors who perform LTK are learning to compensate for this effect by overcorrecting their patients, a technique that both Dr. Belmont and Dr. Kansas use. “I prefer patients to be minimally overcorrected, so I'd rather treat them with less energy,” says Dr. Belmont. She plays down the regressive effect of LTK, saying that regression is to be expected with any hyperopic procedure. “In patients over 40, hyperopia will increase for the life of the patient. So any hyperopic treatment, be it CK, LTK or LASIK treatment, will have its effect decrease over the years because the patient's hyperopia continues as the internal changes in the eye continue to degrade.” She adds that regression is attributable to the natural aging process.
Even LASIK patients experience some regression, although to a lesser degree than LTK. Results of the spherical hyperopia group from Dr. Chayet's study show the average manifest refractive spherical equivalent change from 1 to 3 months, 3 to 6 months, and 6 to 12 months were 0.90 ± 0.35 D, -0.07 ± 0.68 D, and 0.47 ± 0.59 D, respectively.4
Researchers say that there is also a regressive effect following the CK procedure, but that it is due to fluctuations in the tissue as it heals. Dr. McDonald explains that there is a similar overcompensation effect with CK. “There is not regression like we see with LTK, but there is an overshoot. However, I do not consider the recovery from the immediate postop overshoot to be regression,” she says. According to the FDA clinical study for CK, patients average -0.62 D at 1 week postoperatively.
“The amount of regression with CK is comparable to LASIK,” says Dr. Maloney. “Statistically, between 3 and 6 months there's only a quarter diopter of regression; between 6 and 9 months there's a tenth of a diopter; and between 9 and 12 months there's another tenth. There's a slight amount of regression, but it appears to be quite stable.” At 12 months, no eye out of 203 eyes lost two lines of best-corrected vision; and no eye lost more than two lines.5 “Are they going to have the same results 2 and 3 years post-op?” asks Dr. McDonald. “The answer is yes, because we now have U.S. patients that are out 2 years, and we have international patients who are out almost 5 years.”
Comfort and Ease
“It's a completely painless procedure,” says Dr. Belmont of LTK. She explains that there may be some sensitivity from the lesion where the epithelium is removed, but that any discomfort is minimal. “LTK is very user-friendly,” says Dr. Belmont, “both to the physician and the patient. Topical drops are placed in, and the patient sits at an instrument that's very familiar to them, similar to having their eyes examined. Then the laser energy is applied within a few seconds.” She goes on to explain that the procedure places eight spots simultaneously around the cornea in 1.4 seconds, and then repeats the treatment in another 1.4 seconds. “So within 2.8 seconds, 16 spots are completed. I feel it's faster and will have less chance of causing any irregularities in the shape of the cornea.”
While patients find the promise of little to no discomfort an appealing aspect of the LASIK and LTK procedures, CK may produce slightly more discomfort. Dr. Belmont sees this as a drawback to the CK procedure. “In CK, the patient first lies down,” she explains, “and the surgeon has to place a probe in 16 spots around the patient's cornea one by one.” Dr. Maloney suspects that CK may be a little more uncomfortable than LASIK, but that it's only in the immediate postoperative period. “My impression is that there's a little more discomfort with CK than with LASIK the first night,” he says, “but by the next day everybody's comfortable.” He adds that patients might also experience a mild foreign-body sensation on the night of the procedure.
Treating astigmatism. The current perception is that CK can't treat astigmatism, but surgeons in other countries appear to be having success. “Dr. Antonio Mendez of Mexico has been successfully treating astigmatism with CK for nearly 5 years now,” says Dr. McDonald. “The [current] FDA submission has to do only with the spherical correction of hyperopia, but clinical trials will be under way soon for an astigmatism protocol.”
European doctors are also testing an astigmatism protocol for LTK, Dr. Kansas says. “They're attempting to demonstrate that astigmatism can be treated with LTK. They have software where they can fire at certain specific spots, and not have the complete circle. The results of that aren't in yet, but it's logical and it looks promising.”
Market Impact
So how will refractive surgeons who've spent hundreds of thousands of dollars on an excimer laser react to an additional product? Drs. Maloney and McDonald don't expect any resistance. “It won't be a problem because they'll still be using the excimer laser for myopia,” says Dr. Maloney. “In general, I think there's a lot of excitement about the availability of CK. People realize it's a viable alternative to hyperopic LASIK, and it's much more cost-effective than LASIK or LTK,” he says “What I predict,” says Dr. McDonald, “is that people will go to the laser center and use their block time for their myopes, and do their hyperopes in their office at their own leisure.”
Refractec also anticipates a positive response to their new technology. The company asked refractive surgeons how happy they were with the outcomes of treating hyperopia with their excimer lasers, and how interested would they be in trying the ViewPointTM System. According to Ms. Kanner, “The outcome of these two questions was that these doctors were more interested in trying this new technology than they were happy with their current hyperopic outcomes. They responded that if [we] could provide a safer alternative that got similar outcomes, they would purchase it.”
Refractec plans to debut the ViewPointTM System at $48,500, a price that the company derived from market research. “When physicians were asked about price,” says Ms. Kanner, $48,500 was considered a fair price. Our market research also indicates that physicians are more concerned about the potential complications on the hyperopic patient for LASIK, specifically dry eye and flap complications, than they are about the fact that they just spent half a million dollars on a laser.” While there is no fee-per-procedure cost with the unit, there will be a disposable tip cost of $100.
CK's Appeal
With its lower price and ease of use compared with LASIK, CK could be a good procedure to round out a doctor's surgical repertoire. In addition, Dr. McDonald feels that CK offers an opportunity for more general ophthalmologists to become involved with refractive surgery. “I think it's a great way to get into refractive surgery, because the technique is relatively easy,” she says. “There are a few things you have to pay attention to; you can't be sloppy, you can't be cavalier and think that it's so easy that you don't pay attention, but if you adhere to a few basic principles it's really a very easy procedure, and it's a great thing for an experienced LASIK surgeon to have in their surgical armamentarium. It also broadens your patient base.”
Will LTK Suffer?
Some doctors are predicting that CK, which seems to offer more promising stability results, might supplant LTK as the choice treatment for hyperopia. “I think there's a chance that LTK might disappear,” says Dr. McDonald. “I think CK will replace LTK,” concurs Dr. Maloney, “because LTK has been a disappointment in terms of stability.”
Others, however, believe that LTK will continue to hold a place in the hyperopic treatment market, and don't see any reason to make the switch. “I think there's the potential for higher astigmatism [with CK], and I think patients will prefer to have a technique that's applied all at once,” says Dr. Belmont. “I mean, imagine lying down and having a probe stuck in your eye 16 times; most patients will prefer to sit down for a couple seconds and look at a light and have it be done. I think the potential for the astigmatism and the procedure itself really won't have any competition with LTK. I don't think CK is going to take the market share of the over 40 hyperopia low-to-moderate patient.”
Dr. Kansas says that LTK will continue to have something to offer patients. “I think that LTK will get better in terms of flexibility as the software gets more sophisticated and we can target our treatment. Maybe instead of two rings we can do three; maybe instead of eight spots in a circle we could do 16 spots in a circle for a more uniform and optimal response. It seems to me that the potential is there for that.”
Is CK a Threat to LASIK?
For all its improvements on corneal shrinkage, CK cannot treat myopia, and currently LASIK is the only corneal procedure approved in the United States that can treat hyperopic astigmatism. LASIK is also necessary for treating those refractions that are out of range for CK. While patients may be happier with the quality of their outcome with CK, LASIK will continue to be used for hyperopia and hyperopic astigmatism until CK's applications are expanded. “To me, CK and LASIK are complimentary,” says Dr. Maloney, “because CK doesn't treat myopia. I'm most excited about CK for middle-aged and older people because I think it will reduce their instance of dry eye and quality of vision problems.”
Looking Ahead
Once the CK technology is approved, which Refractec is expecting by the end of the year, doctors may start wondering if it will ignite the same price wars that became such a debated topic with LASIK. “Nobody knows what will happen in the marketplace,” says Dr. McDonald, “but I would hope that everybody offers CK at the same price as LASIK. The doctor will make more per case on CK, because the cost per case is lower than with LASIK. It will be interesting to see how it will end
up being priced. There's a huge untapped market out there of people who don't wear glasses, but need to be treated for monovision. This will be a perfect way to tap into that.”
John F. Doane, MD, is in private practice with Discover Vision Centers in Kansas City, MO, and is Clinical Assistant Professor of the Department of Ophthalmology, Kansas University Medical Center. Dr. Doane has been an investigator with several FDA clinical trials for laser techniques. (816) 350-4539; jdoane@discovervision.com
Peter G. Kansas, MD, is currently in private practice at the Kansas Eye Surgery Associates in Albany, New York. He also serves as Clinical Professor of Ophthalmology at Albany Medical College in Albany. Dr. Kansas has performed more than 4,000 refractive procedures and 20,000 cataract procedures. (518) 462-6441
Robert K. Maloney, MD, is founder and former Director of the UCLA Laser Refractive Center at the Jules Stein Institute and current Director of the Maloney Vision Institute. While a professor at UCLA, he trained more than 700 surgeons in the use of the Excimer laser, and he has personally performed more than 20,000 vision correction surgeries. He is a consultant for Refractec. (310) 206-7692; drmaloney@maloneyvision.com
Marguerite B. McDonald, MD, FACS is Clinical Professor of Ophthalmology at Tulane University. She is Director of the Refractive Surgery Center of the South Eye, Ear, Nose & Throat Institute of Memorial Medical Center in New Orleans, LA. Dr. McDonald is the lead clinical investigator for the ViewPointTM System, and is a paid consultant for Refractec. (504) 896-1250; margueritemcdmd@aol.com
1. Chayet AS: Laser in situ keratomileusis for spherical hyperopia, hyperopic astigmatism, and mixed astigmatism. Nidek, 2001
2. Asbell P, McDonald M, Davidorf J, et al: The treatment of hyperopia with conductive keratoplasty (CK). ISRS abstract, 2001
3. Hardten DR: Limits of hyperopic LASIK. ISRS abstract, 2001
4. Chayet AS: Laser in situ keratomileusis for spherical hyperopia, hyperopic astigmatism, and mixed astigmatism. Nidek, 2001
5. Asbell P, McDonald M, Davidorf J, et al: The treatment of hyperopia with conductive keratoplasty (CK). ISRS abstract, 2001
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