Topography-guided LASIK yields predictable, stable refractive outcomes

New software incorporates wavefront, manifest refraction and corneal topography to generate a customized ablation algorithm.

Daniel S. Durrie

A topography-based custom ablation algorithm gives highly predictable results in myopic eyes undergoing LASIK, according to early study results.

Daniel S. Durrie, MD, OSN Refractive Surgery Section Editor, reported 3-month results of a phase 3 clinical trial of topography-guided custom ablation treatment (T-CAT) software used with the Allegretto Wave Eye-Q excimer laser platform (Alcon).

Dr. Durrie spoke at an Alcon sponsored symposium during the joint meeting of the American Academy of Ophthalmology and Middle East Africa Council of Ophthalmology in Chicago.

“We are now providing laser surgery that not only gets people out of their glasses and improves their uncorrected vision and is accurate, but also provides ability to give the patient better vision than they saw with their glasses preop,” Dr. Durrie told Ocular Surgery News in a subsequent interview. “This is the next level of advancement.”

The T-CAT software package has been used in various countries for more than 5 years.

Refractive correction is based on preoperative manifest refraction. Correction of higher-order aberrations and adjustment of asphericity are based on corneal topography.

The algorithm enables the surgeon to design an ablation profile based on topography, wavefront and manifest refraction.

“It moves that information digitally into the software in the laser so that the doctor can now modify the shot profile from the laser using that topography information directly,” Dr. Durrie said. “There is still the information the doctor gets from doing their manifest refraction and phoropter reading. There is still the information from their wavefront reading. But this adds extra information.”

Predictability, stability

The ongoing prospective, nonrandomized clinical trial is being conducted at nine centers in the U.S. The 3-month data included 138 myopic eyes that underwent primary LASIK with T-CAT software. Mean patient age was 34 years.

LASIK with the T-CAT software yielded the most predictable refractive outcomes attained to date, Dr. Durrie said.

“In this particular area, the data from the T-CAT study are as good or better than any data that we’ve seen on the WaveLight laser in the past,” he said. “It matches or exceeds any data that we have seen, not only with the Alcon lasers but other lasers on the market.”

Refractive outcomes were within 0.5 D of targeted values in 92% of eyes and within 1 D of the target in 98%.

“These are very, very strong numbers,” Dr. Durrie said. “We like to see above 90% within 0.5 D.”

At 6 months, 93% of eyes had refractive outcomes within 0.5 D and 99% had outcomes within 1 D of targeted values.

The procedure also enhanced refractive stability. For example, mean manifest refraction spherical equivalent (MRSE) changed 0.026 D from 1 week to 1 month and 0.041 D from 1 month to 3 months. There was no change in absolute cylinder from 1 week to 1 month or from 1 month to 3 months.

Visual acuity, safety

Mean uncorrected visual acuity was 20/16 or better in 75% of eyes at 3 months and 6 months.

UCVA was 20/20 or better in 94% of eyes at 3 months and 93% of eyes at 6 months.

The results also showed strong best corrected visual acuity. For example, 57% of patients had no change in BCVA at 1 month and 44% had no change at 3 months. At 1 month and 3 months, 29% of patients gained one line. Two-line gains were achieved in 11% of eyes at 1 month, 22% at 3 months and 24% at 6 months.

“Almost 50% of people had better best corrected vision after surgery than before at both 3 months and 6 months, which is very impressive,” Dr. Durrie said. “Why would that be? It could be that we’ve added the topography information to the information we already had, so this exceeds the results that we saw with wavefront-optimized surgery. … That is a big deal.”

T-CAT also yielded a high safety profile. Results of a patient questionnaire showed no appreciable increases in subjective visual symptoms such as light sensitivity, night driving difficulty, glare, halos, starbursts, dry eye, pain and foreign body sensation.

The questionnaire showed a statistically significant decrease in the percentage of patients who reported marked or severe glare (P = .0038).

Reductions in night driving difficulty and halos were nearly statistically significant.

“Most people feel that it is solid evidence,” Dr. Durrie said. “In no category did the patient actually get worse.”

The ongoing clinical trial will continue another year before a premarket approval application is submitted to the U.S. Food and Drug Administration.

“It is probably a minimum of 18 months from now before this will be on the market in the U.S.,” Dr. Durrie said. – by Matt Hasson

• Daniel S. Durrie, MD, can be reached at Durrie Vision, 5520 College Blvd., Suite 201, Overland Park, KS 66211; 913-491-3330; fax: 913-491-9650; e-mail: ddurrie@durrievision.com.
• Disclosure: Dr. Durrie is a clinical investigator for Abbott Medical Optics, AcuFocus and Alcon.