Refractive Surgery
Revamped LTK nomogram aims for increased effect
Initial undercorrections, combined with expected refractive drift, made Sunrise PMA data look worse than the technology is capable of, surgeon says.
by Rochelle Nataloni
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January 1, 2000
Editor's note:
Sunrise Technologies is scheduled to reappear before the Food and Drug Administration's Ophthalmic Devices Panel on Jan. 13 and 14. Discussion of the Hyperion LTK System is on the agenda for that meeting.
ORLANDO, Fla. — According to Donald R. Sanders, MD, PhD, of Elmhurst, Ill., an “unfortunate series of [events]” affected Sunrise Technologies' (Fremont, Calif.) laser thermokeratoplasty (LTK) data around phase 2-A of the company's clinical study, resulting in the decision on behalf of the Food and Drug Administration's (FDA's) Ophthalmic Devices Panel not to recommend the Hyperion LTK System for approval.
Dr. Sanders said that although the originally used nomogram from the expanded phase 2A study produced no adverse readings or complications and resulted in good patient satisfaction, there was a tendency to undercorrect virtually all of the patients at 2 years post-treatment.
Dr. Sanders addressed the topic of LTK for hyperopic vision correction here at a Sunrise-sponsored meeting during the annual meeting of the American Academy of Ophthalmology.
Dr. Sanders pointed out that refractive drift is “a fact of life,” regardless of which type of system is used to correct hyperopia — including excimer laser technology. “But the combination of refractive drift and undercorrection made our data look a lot worse than what the [Hyperion] technology is actually capable of,” he said.
A new nomogram
Patient age vs. effect
Analysis of the PMA data allowed Sunrise to develop a new nomogram in an attempt to increase the amount of correction. The new treatment plan, Dr. Sanders said, “is based on the only three factors that seem to affect outcome: the number of applications — whether we use 16 or 32 spots, the patient's age and the amount of energy from the laser.”
Jan A. Venter, MD, a refractive surgeon in South Africa, reported on the outcomes achieved with this new nomogram in 46 eyes with 3 months follow-up. “If we compare these patients who are being treated on the higher energy levels with the FDA studies, we find that there is some improvement in the postoperative visual acuity,” Dr. Venter said. “Seventy-eight percent of the new patients, compared with 65% of the FDA study patients, had postoperative visual acuity” of 20/40 or better.
“We believe that with the introduction of a new nomogram, we will more fully treat these patients and decrease the amount of undercorrection,” Dr. Sanders said. “You're going to see a dramatic improvement in predictability, but even with the old algorithms, we had a very high level of patient satisfaction,” he added.
Dr. Venter also reported on a comparison that he did of 100 patients who underwent hyperopic laser in situ keratomileusis (LASIK) with 100 patients who underwent LTK for 1.75 D to 2.5 D. “We found that the mean postoperative visual acuity of the LTK group was 0.8, and the LASIK group was 0.89. The mean postoperative refraction was 0.45 for the LTK group and 0.27 for the [LASIK] group,” he said.
Frank Goes, MD, of Antwerp, Belgium, has been performing LTK on hyperopic patients using the Sunrise system for more than 5 years, with 400 eyes to his credit. “The results rely on the treatment being done well, and on the indications being respected,” Dr. Goes said. “It is our primary choice in patients who are 40 years or older who have hyperopia up to 2.5 D,” he said.
Dr. Goes pointed out that one of the significant advantages of using LTK rather than LASIK to treat hyperopia is that the central optical zone is left untouched. “With LTK, we can achieve a very large, homogenous optical zone, larger than the best that we could ever obtain after hyperopic LASIK,” he said.
Emanuel S. Rosen, MD, of Manchester, England, said he “wouldn't be without the Sunrise system because it solves so many problems with overcorrections and undercorrections arising from lens surgery, as well as LASIK.” Dr. Rosen pointed out that he is achieving “quite different” results with the new 32-spot treatment plan, while the earlier nomogram also “produced a great deal of satisfaction.
“We are still learning about the nature of the applications – the thickness and thinness of the cornea, the drying [of the cornea],” Dr. Rosen said. “And there are a number of variables for the new nomogram that we are able to control much more effectively.” Dr. Rosen described examples of a variety of patients who benefited from LTK, including one patient who had atypical against-the-rule astigmatism of 3.5 D resulting from an extracapsular cataract extraction. “With LTK, we have an option to treat not only spherical hyperopia,” Dr. Rosen said, “but cylindrical hyperopia, as well.”
Laser energy and effect
Dr. Sanders illustrated the relationship between applied laser energy and effect by describing the type of outcome that could be achieved with both a 16-spot treatment and a 32-spot treatment. “There is a linear relationship between applied laser energy and effect,” Dr. Sanders said. “For a 55 year old, using a 16-spot treatment and 240 mJ, you could expect slightly less than 1 D of effect. With a 16-spot case and 300 mJ, you could achieve slightly over 2 D.”
Using 32 spots increases the effect dramatically, Dr. Sanders said. “In a 55-year-old patient using the 32 spots, you could go all the way up to the 300 mJ range and achieve as much as 5 D of effect,” he said. “In the U.S. studies that we did, we went up to approximately 260 mJ, and that resulted in a little bit more than 1 D of effect in a 16-spot case, and almost 3 D of effect in a 32 spot case.”
Patient age is a significant factor. In a 40 year old, a 16-spot case using 258 mJ of treatment would achieve 1 D of effect; while in a 70 year old, that same treatment plan would result in 1.5 D of effect, Dr. Sanders reported. A 32-spot case using 258 mJ in a 40 year old would achieve 2.25 D; while that same treatment plan in a 70 year old would result in 3 D of effect.
Sunrise has submitted a protocol to the FDA to perform 32-spot cases. The new protocol is for hyperopia ranging from 2.25 D to 4 D. “We essentially do the 16-spot treatment twice,” Dr. Sanders said. “Sequentially, we do eight spots at 6 mm, another eight spots at 7 mm, and then we rotate the beam and do another eight spots at 6 mm, and another at 7 mm,” he explained.
Sunrise LTK has not resulted in vis ion complications or adverse reactions. “Clearly, the safety of the procedure has been extraordinary,” Dr. Sanders said. “These patients had marked improvement in uncorrected acuity, refractions that were much closer to emmetropia than when they started, and they en countered no significant safety issues.”
For Your Information:
Frank Goes, MD, can be reached at the Antwerp Eye Centre, Willem Klooslaan 6, Antwerp, 2050, Belgium; (32) 3-219-3925; fax: (32) 3-219-6667; e-mail: frankgoes@club.innet.be. Dr. Goes did not disclose whether or not he has a direct financial interest in any of the products mentioned in this article or if he is a paid consultant for any companies mentioned.
Emanuel S. Rosen, MD, can be reached at 10 St. John St., Manchester M3 4DY, England; (44) 161-8328778; fax: (44) 161-8321486. Dr. Rosen has a small shareholding in Sunrise Technologies Inc.
Donald R. Sanders, MD, PhD, can be reached at 180 W. Park Ave., Elmhurst, IL 60126; (630) 530-9700; fax: (630) 530-1636. Dr. Sanders has no direct financial interest in any of the products mentioned in this article. He is a paid consultant for Sunrise Technologies Inc.
Jan A. Venter, MD, can be reached at Port Elizabeth Eye and Laser Institute, 205 Kaap Road, Mill Park, Port Elizabeth, South Africa; (27) 41-333-532; fax: (27) 41-3737-193. Dr. Venter did not participate in the preparation of this article.
Sunrise Technologies Inc. can be reached at 3400 W. Warren Ave., Fremont, CA 94538; (510) 771-2389; fax: (510) 771-2292.
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