May 2014

 

REFRACTIVE SURGERY

 

Refractive editor's corner of the world

The current state of topography-guided ablations


by Ellen Stodola EyeWorld Staff Writer

 
 

We have been fortunate that over the past decade, ophthalmology has benefited from capitol investments into research and development to aid in the advancement of technology. A great example of this is refractive surgery, specifically LASIK. Recently, topography-guided ablations received clearance by the FDA. This technology has the potential to help those patients who have had previous LASIK surgery and have unwanted side effects. This is a common use for topography-guided treatments outside of the U.S. and has been for more than 10 years. However, there is no data in the U.S. clinical trial to support the use of topography-guided LASIK after previous LASIK. The results from topography-guided LASIK on virgin eyes were not only comparable, but in some ways surpassed other approved treatments. This can and should be a first-line treatment for virgin eyes undergoing LASIK. How about previously treated eyes? We will have to look with caution, as our guests discuss in this month's "Refractive editor's corner of the world." Thanks to Drs. Cummings and Durrie for their insights into topography-guided ablations.

Kerry Solomon, MD, refractive editor

 

Figure 1: This ablation includes the topography data as well as the refractive data of 1.25 D sphere. It can clearly be seen that the ablation is not symmetrical.

Figure 2: The same ablation as in Figure 1 but the refractive data has been removed. This is the topography-derived data (higher order ablation profile) only, and the surgeon needs to determine what effect this ablation will have on the refraction and then modify the refractive data to be used in the ablation.

Source: Arthur Cummings, MB ChB

Approvals and patient selection recommendations differ depending on where topography-guided ablation is being used

Topography-guided ablation has different applications around the world. It was only recently U.S. Food and Drug Administration approved, specifically for patients who have not undergone previous surgery. In Europe, it has been used for the past 10 years, and its applications expand to patients who are undergoing retreatments. Arthur Cummings, MB ChB, MMed(Ophth), FRCSEd, Wellington Eye Clinic, Dublin, discussed the use of topography-guided ablations and his experiences, while Daniel Durrie, MD, Durrie Vision, Leawood, Kan., discussed the recent approval in the U.S. and how it will come into play in the future.

Uses

Topography-guided ablations can be useful in various types of cases. "We've had them since 2004, so the last 10 years, we've used them mostly for complicated cases," Dr. Cummings said. It's generally used for retreatments in someone who has had previous LASIK or PRK and who has a small or decentered optical zone, he said. Topography-guided ablations can help to recenter or reenlarge the optical zone. Dr. Cummings also uses topography-guided ablation for select keratoconus patients, combining it with simultaneous crosslinking. Topography-guided ablation may be used slightly differently in Europe than in the U.S., in part because of its recent approval for first-time treatments only in the U.S.

What the public needs to understand about the U.S. clinical study and approval is that it was done on eyes that did not have previous surgery, Dr. Durrie said. This means that the topography-guided ablation trial targeted eyes that are the standard myopic eyes with astigmatism that are having surgery all the time, with the goal of seeing if it is comparable to the standard treatment and if there are any advantages.

The trial focused on patients coming in for regular surgery, and they did extremely well, Dr. Durrie said.

Advantages and disadvantages

"The advantage of topographies is that you can get very good repeatable data," Dr. Cummings said, indicating that whole eye wavefront- derived data is simply not as repeatable. Outside the U.S., there are two systems that can generate topography-guided ablation, he said.

One is based on Placido disk, the Topolyzer (Alcon, Fort Worth, Texas); the other is based on Scheimpflug, the Oculyzer (Alcon). In the U.S. clinical trial, only the Topolyzer was used.

"Even though they're two different systems, they almost invariably come up with the same treatment plan," Dr. Cummings said. With the Scheimpflug device, it does not matter if the eye is slightly dry, while the other is more dependent on a good tear film and has slightly less good data in the middle due to the scotoma caused by the centrally placed camera on the Topolyzer.

Even though one system might be better than the other in a particular situation, when you look at the ablation profile that the maps have generated, they normally look identical, Dr. Cummings said. Where there is missing data, the systems usually fill in the gaps.

The disadvantage with topography-guided ablation, Dr. Cummings said, is that especially in a complicated eye, the key treatment is regularization of the cornea, and it is not always clear the effect this will have on refraction.

The topography-guided retreatment procedure is less predictable in what kind of refraction you are going to get, he said, recommending that surgeons using topography-guided ablation treat it as two stages, first using it with no refractive input to simply regularize the cornea. Then after 6 months, there will be better surface and endpoint refraction and the refractive component could be treated.

Dr. Durrie said that results in the U.S. were extremely good. One thing that stuck out in the data was that patients seemed to have less night glare and halos than had been seen in other clinical trials. The results were not only as good as other clinical trials with this technology, but they had some distinct high-quality vision results. However, he stressed that currently in the U.S., this approval only applies to "normal virgin eyes" because all data from the clinical trial is from eyes that had not undergone previous surgery. "There may be surgeons who use this off label, but they should know there is no data in the U.S. clinical trials to support that," he said.

Pearls

Dr. Cummings said that surgeons must make sure that patients are well informed about the technology. Tell patients you are trying to make the cornea more regular, which will lead to better vision once you have corrected with glasses, contacts, or another treatment option, he said.

"I think you need to spend time going on a training course where you can learn more about how to predict what the refractive effect is going to be of the regularizing procedure," Dr. Cummings said. He added a warning that "it's a very powerful tool, and the laser's going to do exactly what you ask it to do." It's important to know what it is going to do and be sure you have read the ablation profile, he said. The key pearl that Dr. Durrie offered is "if it's a topography-driven treatment, surgeons need to make sure they have excellent topography." Normally topography is used as a diagnostic screening tool, and now it is being used as a therapeutic tool.

Make sure you have the right topography and that it is done properly, he said.

Compared to wavefront

The main difference between wavefront and topography data is that wavefront is based on the optics just through the pupil, while topography data is based on the corneal surface. It may be hard to get good wavefront data for complicated patients because the corneal aberration is so high; it might be necessary to use topography-guided in these patients, Dr. Cummings said.

The U.S. clinical trial did not look at any head-to-head comparisons of topography-guided ablations and wavefront. Because there have been trials on wavefront-optimized, wavefront-guided, and topography-guided, Dr. Durrie said there is data to be reviewed in the future on this topic. EW

Editors' note: Dr. Cummings has financial interests with Alcon (Fort Worth, Texas). Dr. Durrie was an investigator in the topography-guided ablation U.S. clinical trial.

Contact information

Cummings: abc@wellingtoneyeclinic.com
Durrie: ddurrie@durrievision.com

The current state of topography-guided ablations The current state of topography-guided ablations
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