Innovation Spotlight - Laser Thermal Keratoplasty

Laser thermal keratoplasty helps correct hyperopia

Early results of the holmium laser study show good correction outcome for low hyperopia

Manus C. Kraff, MD

By Alyson G. Yashar, MD
Reviewed by Ernest W. Kornmehl, MD

Chicago-The Sunrise holmium laser for corneal shaping shows promise for low to moderate hyperopia, according to a phase III study.

While target correction was attained more frequently in patients with low hyperopia, equal or greater improvement in vision was achieved in patients with moderate hyperopia, and these patients were equally satisfied after treatments with the holmium laser, reported Manus C. Kraff, MD, professor of clinical ophthalmology, Northwestern University, Chicago.

"This procedure represents an extremely noninvasive approach to hyperopia. And it does not preclude other procedures," said Dr. Kraff, who is one of 12 ophthalmologists involved in this ongoing study.

The enrollment criteria included preoperative hyperopia of 0.75 to 2.50 D. In this study, low hyperopia was defined as 0.75 to 1.99 D, and moderate hyperopia at 2 to 2.50 D. All patients were older than age 40 and had a stable refraction. As of July 1999, there were 656 eyes enrolled in the study. UCVA was 20/30 or worse

How the procedure works

The laser thermal keratoplasty (LTK) procedure involved the use of the holmium laser to place two concentric eight-spot rings on the cornea, with diameters of 6 and 7 mm. Seven pulses at a frequency of 5 Hz were used, with pulse energy of 226 to 258 mJ.

The Sunrise holmium laser has met efficacy, stability, and safety endpoints (target values) for hyperopic laser procedures. Prior to the phase III trial, in conjunction with investigators, the sponsor developed prospective effectiveness endpoints for the FDA-approved protocol.

"Investigators believed that an improvement from baseline refraction and vision was more important to the patient than attaining a specific target. In other words, improved UCVA was more important than maintenance of BCVA," Dr. Kraff said.

So far, there has been a reduction of hyperopia by at least 0.5 D at 6 months compared with pretreatment. UCVA at 6 months or later improved by two lines or more.

This procedure also was found to be safe. Only 0.4% of eyes lost two lines or more at 6 months and 12 months. Three eyes lost vision, however, none of these cases was due to laser-related complications. Two were due to age-related cataracts that had increased, and one patient had a transient decrease in visual acuity from 20/13 to 20/20. One patient complained of a foreign-body sensation at 6 months and a few others experienced a mild scratchy feeling. There were no laser-related adverse effects.

Only 0.8% of eyes had 2 D of induced astigmatism at 6 months, and this figure dropped to 0.2% at 12 months. Although there are no target values for 1 D or less of astigmatism, at 1 year, the target value of 1 D of induced astigmatism is less than that of the FDA target value for 2 D of astigmatism. Eighty-six percent of patients in this study reached the FDA target value of 20/40 vision at 6 months. At the end of 18 months, about 40% had UCVA of 20/20, Dr. Kraff said.

"The rapid change is between 1 and 4 months, where you lose 0.35 D of correction," noted Dr. Kraff. "Between 3 and 9 months, you only lose 0.6 D, and it really flattens out. You lose about 0.3 or 0.6 D at 24 months, so the mean rate of change decreases progressively to about 0.3 D between 18 and 24 months. The rate of regression never exceeds 0.1 D per month."

When comparing regression or drift with other published studies, the Sunrise study is comparable to other techniques and other studies for low hyperopia, Dr. Kraff noted. The refractions were stable when defined by a change of less than or equal to 1 D of manifest spherical equivalent between two refractions performed at least 3 months apart in at least 95% of cases. This study meets the FDA criterion for stability, he said.

Dr. Kraff said that he believes this procedure is extremely safe.

"The preservation of BCVA is unsurpassed. The reported complications are minimal. The risk of ocular complications is negligible due to the noninvasive technique," he said. "There were no adverse laser effects. The incidence of induced cylinder was well within the FDA target range. The U.S. clinical study clearly demonstrates efficacy, predictability, and stability."

Sunrise is working on long-term data and a new predictability algorithm to increase and enhance the clinical outcomes. The FDA has approved a new study for mid-range hyperopia that has expanded this to 2.50 to 4 D using a 32-spot treatment to produce an increased effect, Dr. Kraff said. He has no financial interest in this topic.

Ophthalmology Times / APRIL 15, 2000