Study: Nidek software produces good results in unoperated eyes

Latest software for the NAVEX platform combines earlier programs for best results, but it needs evaluation.

New software for the Nidek wavefront platform produces good visual outcomes with stable postoperative vision, but its success in reducing higher-order aberrations must still be evaluated, according to researchers in Mexico.

Arturo Chayet, MD, and colleagues at the Codet-Aris Vision Institute in Tijuana, Mexico, presented their 6-month results with the OPDCAT (Optimized Path Difference Customized Aspheric Treatment) ablation algorithm at the meeting of the American Society of Cataract and Refractive Surgery in Washington.

The researchers studied a group of 76 eyes treated with the OPDCAT algorithm, which was developed for the Nidek Advanced Vision Excimer (NAVEX) laser system.

The study group included patients with myopia of up to –6.5 D and astigmatism of up to –3 D.

The eyes in the study had a mean preoperative spherical equivalent of –2.98 D, a mean preop sphere of –2.66 D and a mean preop cylinder of –0.64 D.

The difference between conventional profiles (left) and wavefront profiles (right). A larger optical and transition zone exists in wavefront treatments because of the aspherical profile. Images: Chayet A

‘Great’ stability

At 6 months postoperatively, the mean spherical equivalent improved to –0.15 D, the mean sphere to –0.11 D and the mean cylinder to –0.08 D.

At the 6-month follow-up, 67% of eyes had an uncorrected visual acuity of 20/16 or better, and 97% of eyes had UCVA of 20/20 or better.

All eyes were within 1 D of the intended refraction, and 84% of eyes were within 0.25 D of the attempted refraction.

“We saw great stability with no regression of the effect from month 3 to month 6,” Dr. Chayet said.

The procedure also proved to be safe, with 68% of treated eyes showing no loss of best corrected visual acuity and 17% gaining one line of Snellen acuity, he said.

Mesopic contrast sensitivity data showed equal or better postoperative results as compared to preoperative conditions.

He said the effectiveness of the OPDCAT program on higher-order aberrations is as strong as can be expected from current systems.

“It is as effective as any other system on the market. I don’t really think there will soon be a system that will considerably reduce the higher-order aberrations,” he said.

“OPDCAT software … produced very good visual outcomes along with excellent quality of vision,” Dr. Chayet said in his presentation. “The role and impact of decreasing the higher-order aberrations remains to be evaluated.”

Best in virgin cases

A typical OPDCAT treatment. The 1-mm multipoint ablation is used to treat the high-order aberrations and then is followed by the prescription treatment.

The OPDCAT algorithm, developed and first used in 2004, is the third in a line of algorithms for the NAVEX platform.

According to Dr. Chayet, the OPDCAT algorithm combines the benefits of the earlier OATz and CATz algorithms; the concept behind this combination is to reduce the total ablation depth by maintaining corneal asphericity, to prevent postoperative aberrations and to treat higher-order aberrations of the entire optical system.

“With the OPDCAT algorithm, the central zone is aspheric as well as the transition zone, so the entire treatment is truly aspheric,” he explained.

The OATz algorithm is used to remove spherical aberrations in the central optical zone and aspherical aberrations in the peripheral transition zone. According to Dr. Chayet, aspheric ablations with OATz are meant for previously unoperated eyes with a small number of irregularities.

CATz is primarily for re-treatments or eyes with corneal irregularities and is based on the topography of the cornea. Dr. Chayet said the irregularity component with this program should be kept at or under 40 µm.

“CATz is primarily used to treat decentered ablations or central islands, problematic cases,” he said.

According to Dr. Chayet, while CATz still has its place as a secondary, topography-based treatment, OPDCAT replaces any need for the OATz program.

“If you want to use one treatment for everything, you would use the OPDCAT, except if you want to re-treat problems that are only at the corneal level, then you would use CATz. OPDCAT you would use for all virgin cases,” he said.

Contraindications

Ophthalmologists using the OPDCAT ablation profile must be mindful of pupil artifacts at the edge of the OPD map, Dr. Chayet cautioned.

When pupil artifacts exist, the algorithm should not be used, he said.

Because the OPD data is used to extract higher-order components, the map should be free of “noises” in the periphery.

“You need to make sure there are no issues with the tear film or anything that produces pupil artifacts. So if you have pupil artifacts, then your measurement will not be that good. It could be misleading,” he said. “The only thing you need to do is make sure that everything you took with your scan is appropriate.”

Dr. Chayet suggested taking OPD measurements in a dark room and under conditions appropriate for wavefront systems, or using a mydriatic agent before taking the measurement. He emphasized the importance of technique when capturing the OPD map.

“You need to have a very good measurement with a very good pupil,” he said.

The OPDCAT system is not yet approved by the Food and Drug Administration.

For Your Information:

• Arturo Chayet, MD, can be reached at Codet-Aris Vision Institute, Padre Kino 10159, Tijuana, Mexico 22320; 52-664-683-5723; fax: 52- 664-682-4096. Dr. Chayet has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

• Nidek, maker of the OPDSCAN algorithm for the NAVEX system, can be reached at 34-14, Maehama, Hirosihi-cho, Gamagori, Aichi 443-0038, Japan; 81-533-67-6611; fax: 81-533-67-6610; e-mail: info@nidek.co.jp.

• Jared Schultz is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses geographically on Europe and the Asia-Pacific region.