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Emerging refractive surgeries: safer, less invasive than LASIK, studies show
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LOS ANGELES — Although LASIK remains at the forefront of refractive surgery, new technologies in vision correction are continually being developed. These alternatives to LASIK, which are at varying stages of the Food and Drug Administration (FDA) approval process, boast increased safety, few complications and a high rate of success.
Among the most prominent technologies currently being developed are Intacs prescription inserts (Addition Technology, Fremont, Calif.), laser thermal keratoplasty (LTK) and radio frequency keratoplasty.
Intacs: new indications
Intacs micro prescription inserts are currently being touted as minimally invasive and safe for certain levels of myopia. Currently FDA approved for use in patients with 1 to 3 D of myopia, Intacs are placed at approximately two-thirds depth of the cornea within the stromal lamellae.
“Intacs flatten the cornea very effectively,” said Brian S. Boxer Wachler, MD, director of the University of California-Los Angeles Laser Refractive Center at the Jules Stein Eye Institute. “And they do so without disturbing the central visual axis of the cornea.”
Dr. Boxer Wachler said FDA approval for an expanded range of myopia correction is currently being sought for Intacs. “It is hoped that the FDA will eventually approve Intacs up to a correction of –4.5 D,” he said. “Phase 3 clinical trials have been completed for those ring sizes.”
Dr. Boxer Wachler said that in addition to being less invasive, Intacs are easily replaceable in different sizes, a feature that appeals to myopes within the indicated range.
“Many patients in this range of myopia may be apprehensive about LASIK, but they are comfortable with Intacs, because they are less involved,” he said. “And depending upon the surgeon, they can certainly be as effective as LASIK.”
Intacs for keratoconus
One of the most promising new applications of Intacs is for treating keratoconus. Although they are not yet FDA-approved for this indication, Intacs have been used quite successfully for this purpose, Dr. Boxer Wachler said.
“Right now, this is one of the single most exciting developments in the field,” he said. “The results show that a significant number of patients gain best-corrected acuity, as well as uncorrected acuity.”
Dr. Boxer Wachler said he has treated more than 100 cases of keratoconus as an off-label use of Intacs. “It’s just like the lasers in the beginning,” he said. “They weren’t approved for LASIK, but doctors were using them off-label. That is essentially what I have been doing with Intacs for keratoconus.”
Dr. Boxer Wachler said he is currently involved with a formal FDA study, which will evaluate this use of Intacs for the purpose of obtaining FDA approval for the keratoconus indication. “Based on my own results, I think the patients have significantly benefited,” he said. “For keratoconus, I use different thickness segments, to cause more flattening underneath the cone. It has worked very well.”
Additionally, Dr. Boxer Wachler said he has used Intacs for residual myopia after LASIK, with a high level of success. He has also used Intacs for patients with post-LASIK glare and halos, which are associated with a small treatment zone on the cornea. “Intacs have turned out to be helpful in correcting some LASIK complications,” he said.
Another of these complications is naturally occurring post-LASIK keratoconus, known as ectasia. “This is a keratoconus induced by LASIK, where the laser went too deep into the cornea and actually destabilized it,” he said. “The Intacs have helped this as well, because they act as they do for keratoconus.”
The FDA studies involving the use of Intacs for keratoconus are expected to begin within the next month or two, Dr. Boxer Wachler said.
“The keratoconus use has been very exciting,” he said. “The myopia use is the bread and butter right now, but it is certainly going to continue to grow for keratoconus.”
Laser thermal keratoplasty
LTK is a surgical treatment for hyperopia that heats the tissue in the cornea, causing it to shrink slightly. In 2000, Sunrise Technologies’ (Fremont, Calif.) Hyperion LTK system was approved by the FDA.
“In clinical practice, spots of heat are being placed in the mid-periphery of the cornea,” said Douglas D. Koch, MD, professor of ophthalmology at the Cullen Eye Institute at Baylor College of Medicine. “These spots steepen the central cornea, thereby increasing its curvature and correcting hyperopia.”
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Dr. Koch was the medical monitor for the Sunrise Hyperion system and led it through clinical trials. “One advantage of this approach is that it is extraordinarily safe,” Dr. Koch said. “There have been no patients with sight-threatening complications.”
Dr. Koch said for some patients, the correction is very effective and can last many years, if not permanently. “The negative part of it is that you are placing the cornea under some tension and stress because the heat causes the tissue to contract,” he said. “That requires the patient to be overcorrected somewhat, early on in the procedure, so that he or she will have a little bit of myopia after the procedure. Then, the patient regresses a little bit, to what you hope will be a good result.”
Unfortunately, Dr. Koch said, some patients regress completely, or to the extent that they require additional treatments. “In other words, you make them myopic, and they regress right back to farsightedness — the effect doesn’t last,” he said. “Among my patients, the best candidates are those who have hyperopia up to about +1 to +1.5, because even if there is partial regression for those low corrections, patients will often have excellent uncorrected visual acuity, and they’re very happy.”
Dr. Koch said there are not yet solid data regarding the rate of complete hyperopic regression. “We don’t have much long-term data beyond 2 years to know which patients end up permanently regressing and which hold a good correction,” he said. “In the U.S. study, we had to retreat about 10% to 15% of the patients, but the regression is higher than that. I’d say at least 50% of patients will need a second treatment.”
Dr. Koch maintained that LTK is more viable for patients needing lower corrections, because these patients can hold a good correction even if they regress somewhat. “Right now, it is not viable for the +2 to +2.5 range, even though it is approved for that level,” he said.
Dr. Koch cited safety as one of the main advantages of LTK. “It’s extraordinarily safe,” he said. “There are no flap problems, no infections. From that standpoint, it has it all over LASIK.”
Additionally, Dr. Koch said, patients who regress after LTK can still opt to try LASIK. “That’s another advantage of LTK — if it doesn’t work, you can do LASIK over it,” he said. “It doesn’t close that door.”
Radio frequency keratoplasty
Refractec’s (Irvine, Calif.) ViewPoint CK system for conductive keratoplasty was recommended for approval on Nov. 30, 2001, by the FDA’s Ophthalmic Devices Panel. The system uses radio frequency energy to treat spherical hyperopia between 0.75 D and 3 D.
“The energy is sent into the cornea through a thin probe that is only 90 µm wide, which is pushed down into the cornea at 8, 16, 24 or a maximum of 32 treatment spots in the peripheral cornea,” said Marguerite B. McDonald, MD, director of the Southern Vision Institute in New Orleans and clinical professor of ophthalmology at Tulane University. “When the energy is released into the cornea, the impedance heats the cornea to create a deep, consistent columnar lesion. There is no temperature gradient.”
Dr. McDonald pointed out that with other forms of thermal keratoplasty, the corneal surface gets heated, but a few microns down the temperature begins to attenuate. “There is a marked temperature gradient and not a very deep or consistent treatment with other forms,” she said. “This one is very deep. The probe is 450 µm long and is 90 µm wide. Basically, there is a 500-µm by almost 200-µm wide treatment zone.”
This causes a cinching, belt-like effect in the mid- peripheral cornea, Dr. McDonald explained. “So, the central cornea gets steeper and the far-peripheral cornea gets flatter, which is why it’s used to treat hyperopia,” she said.
Clinical findings for CK
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Dr. McDonald cited the most recent clinical trials of Refractec’s ViewPoint CK system: a phase III clinical trial that involved 233 patients and 401 eyes. The mean age was 55, with a range of 40 to 74 years. The patients had between 0.75 and 3.00 D of hyperopia, with less than 0.75 D of astigmatism. The intended outcome was emmetropia. Dr. McDonald said the mean preoperative cycloplegic refraction spherical equivalent was +1.86, and the mean preoperative manifest refraction spherical equivalent was + 1.80.
“The surgery is very easy and quick,” Dr. McDonald said. “It usually takes less than 3 minutes. You instill topical anesthesia and a few eye drops and insert a speculum, which is the return path for the energy. Then you mark the eye and apply treatment.”
Dr. McDonald reported that at 1 year with single treatments only, 56% of the patients were 20/20 or better uncorrected, 75% were 20/25 or better and 92% were 20/40 or better.
Dr. McDonald added that at 1 year, 63% of patients were ±0.5 D of intended outcome, 89% were ±1 D and 99% were ±2 D. “Uncorrected acuity does change over time and continues to improve,” she said. “We see no plateau at 12 months.”
However, the ophthalmic devices panel was not convinced that the procedure could maintain a refractive change (though 93% of the effect remained at 1 year because long-term data was not available yet). The panel gave its approval upon the condition that the labeling for the ViewPoint CK include the wording, “for the temporary reduction of hyperopia.”
Dr. McDonald maintained that the procedure has shown itself to be not only safe, but also successful. “We feel this is a highly effective procedure, comparable in efficacy to hyperopic LASIK,” she said. “It is incredibly safe, and you are not operating over the visual axis.”
For Your Information:
- Brian S. Boxer Wachler, MD, is the director of the UCLA Laser Refractive Center at the Jules Stein Eye Institute. He can be reached at 100 Stein Plaza, Los Angeles, CA 90095; (310) 825-2737; e-mail: bbw@jsei.ucla.edu. Dr. Boxer Wachler has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Douglas D. Koch, MD, is a professor of ophthalmology at the Cullen Eye Institute at Baylor College of Medicine. He can be reached at Cullen Eye Institute, Baylor College of Medicine, 6550 Fannin, Houston, TX 77030; (713) 798-6443; fax: (713) 798-3027. Dr. Koch has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Marguerite B. McDonald, MD, is director of the Southern Vision Institute in New Orleans. She can be reached at 2820 Napoleon Ave., Ste. 750, New Orleans, LA 70115; (504) 896-1240; fax: (504) 896-1251. Dr. McDonald has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned.
- Addition Technology Inc. can be reached at 48630 Milton Dr., Fremont, CA 94538; (510) 353-3000; (877) 888-5372.
- Sunrise Technologies can be reached at 3400 W. Warren Ave., Fremont, CA 94538; (510) 771-2389; fax: (510) 771-2292; Web site: www.sunrise.md.
- Refractec can be reached at 3 Jenner, Suite 140, Irvine, CA ; (949) 784-2600; (800) 752-9544; fax: (949) 784-2601; Web site: www.refractec.com.