Study: LTK effects are shown to be 'permanent'

Issue: May 1, 2001

KOLOA, Hawaii — Effects of laser thermal keratoplasty have been shown to be permanent, and regulatory authorities are being asked to change the procedure’s labeling accordingly, it was reported here.

“There is no way that this procedure can be considered temporary, because the effect stays,” said Donald R. Sanders, MD, PhD, an associate professor at the University of Illinois-Chicago.

Dr. Sanders said Sunrise, manufacturer of the Hyperion laser used in laser thermal keratoplasty (LTK), has petitioned the Food and Drug Administration (FDA) to remove the term “temporary” from the labeling of the LTK procedure. He described new data on LTK in a symposium supported by an educational grant from Sunrise Technologies in association with Hawaii 2001, the Royal Hawaiian Eye Meeting, sponsored by Ocular Surgery News in conjunction with the New England Eye Center.

“Our next step is just to wait for the bureaucracy to wind its way and get rid of this term, which was sort of foisted upon the company based on what I think was a misunderstanding of some of the data,” he said.

Temporary versus permanent

According to Dr. Sanders, a problem with the labeling has been the interpretation of what the word “temporary” means.

Effect of age on predicted outcome 2 D attempted correction, high power.

“One of the things we showed was ... that in terms of longevity of the procedure, if you use more than 238 mJ of power, when you do the longevity curves, the effect actually lasts 15.5 years. This data was presented to the FDA and, as many of you are aware, there has been a big flap about the use of the word ‘temporary’ with the Sunrise machine,” he said.

After showing new data to the FDA, Sunrise was able to convince the FDA to allow a change in the labeling of the procedure.

“This data convinced the FDA to change the label to indicate that the Sunrise LTK procedure lasts 10 years and beyond. So the current label says ‘temporary’ but it lasts longer than 10 years. Well, everything depends on your definition of ‘temporary’,” he said.

Age-power interaction

Expected refractions of patients 55-years-old at +1.25 D with three different energies.

One factor that strongly affects the outcome of LTK is the amount of laser energy applied to the eye. “As you increase the energy, you increase the amount of effect,” Dr. Sanders said.

Another factor is age. As patients get older, they experience more effect from the procedure.

“One other factor that I think is important is that there is a relationship between both age and power,” Dr. Sanders said. “Basically, if you use a fairly lower power in younger patients, you get a little bit more effect early on, but it regresses more. The younger patients do have more regression, so that if you use the very lowest power available you get very little residual effect at 24 months.”

According to Dr. Sanders, older patients get less initial effects but much more substantial residual effects.

“So the younger patients don’t appear to respond as well to the lower powers,” he said. “If you use a lower power, what basically happens is you get less initial overcorrection and it results in less late effect. If you use more power, you get more initial overcorrection and you get more final effect. So one has to choose how much power you use based on what you want. If you are willing to accept the fact that you’re going to have some or more initial myopia, then use more power.”

Algorithms

According to Dr. Sanders, Sunrise has developed a software package that provides three different endpoint algorithms that will provide emmetropia at 6 months, 12 months or 24 months.

“The major difference is that the 6-month algorithm provides less energy, less initial overcorrection and therefore less late residual effect. The 24-month algorithm is more energy, more initial overcorrection and more residual effect,” he said.

Dr. Sanders recommends using the 6-month algorithm.

“These were developed at a time when the FDA did not allow for re-treatments,” he said. “The current thinking of virtually all of the investigators is that the 6-month emmetropia algorithm is the one that should be used. This is what should be started with and if somewhere between 18 to 24 months the patient requires more effect, a simple re-treatment or enhancement is very easy to accomplish. That seems to be the general wisdom of the users and I think it’s working out very well.”

For Your Information:

Donald R. Sanders, MD, PhD, can be reached at 180 W. Park Ave., Suite 150, Elmhurst, IL, 60126; (630) 530-9700, fax: (630) 530-1636; email: donaldrsanders@mediaone.net. Dr. Sanders is a paid consultant for Sunrise.

Sunrise Technologies can be reached at 3400 W. Warren Ave., Fremont, CA 94538; (510) 771-2389; fax: (510) 771-2292; website: www.sunrise.md.