Nidek calls their wavefront and customised laser system NAVEX  (Nidek Advanced Vision Excimer laser system).

It has 3 main methods: 1. OATZ (Optimised aspheric transition zone) This keeps the cornea more prolate than the normal laser software and is used for eyes with lower levels of irregular aberrations. 2. CATZ (customised aspheric transition zone) - this is used in eyes with irregular corneae e.g. from disease or prior surgery. 2. OPD-CAT - full aspheric wavefront guided treatment with correction of the smaller irregularities in virgin eyes. This is useful where eyes have greater than average irregularities (higher order aberrations).

I do most normal eyes with OATZ, and if the higher order aberrations are significant, then I use OPD-CAT. With OPD-CAT, it is important to have good "registration"  of the eye - i.e. the small irregular ablations should be in the correct place on the cornea. This is helped by having "iris registration" .  This is a system on the laser that lines it up with the unique marks that we all have on our irises. This is like a bar code arranged in a circle and ensures that the eye is not twisted out of alignment.

In the recent Nidek congress in Barcelona (June 2004), there were a number of very good presentations of the OATZ (optimised aspheric transition zone) software. This keeps the cornea more prolate than the normal laser software. 

Professor Alaa El-Danasoury from Saudi Arabia had treated a group of patients, one eye with the normal Nidek software and the other eye with the OATZ software. 50% preferred the OATZ eye. 17% preferred the conventional one and 33% could not tell the difference. This was mostly due to the slightly better quality of night vision. OATZ is especially recommended for larger prescriptions, (about over -6 D), low light pupils greater than 6mm, minimal irregularity and well corrected vision with glasses.

As part of a multi center international study of the Optimized Aspheric Transition zone (OATZ) here I will present my experience with this treatment. OATz was designed to address the issue of spherical aberration post ablation. LASIK for myopia and astigmatism was performed on 80 eyes. Preoperative sphere ranged up to –5.75 D and cylinder up to –3.25 D. Eighty three percent of the eyes were available for follow up at 3 months postoperatively. Ninety-seven percent of the treatments were within +0.50D of the intended yielding highly accurate outcomes (Figure 1). Uncorrected visual acuity at three months postoperatively is shown in figure 2. Ninety four percent of the patients achieved 20/20 or better.

The OATz ablation algorithm was safe with approximately thirty percent of the patients gaining lines of best-corrected visual acuity (Figure3). Subjectively, patients expressed a very high degree of satisfaction with the OATz treatments, some remarking that their vision was even better than their preoperative vision with contact lenses. These results are supported by preliminary contrast sensitivity data that shows up to 26% of patients gained contrast levels within a month after OATz treatments. These results support the safety and accuracy of the treatment of myopia and astigmatism by the NAVEX Platform

A recent study conducted by Minamiaoyama Eye Clinic in Japan found that the use of the Optimized Aspherical Treatment Zone (OATz) leads to greater patient satisfaction than conventional treatments. The study team included, Yoshiko Hori-Komai MD, Ikuko Toda MD, Naoko Asano-Kato MD, Mitsutoshi Ito MD, Akihiro Yamamoto MD, and Kazuo Tsubota MD, who compared the outcome of OATz LASIK with that of conventional ablation. The NAVEX platform, which consists of the NIDEK EC-CX Excimer laser equipped with a 200 Hz eyetracker, and the NIDEK OPD-Scan, was used to treat all the patients. Approximately one hundred patients in both groups were studied and the preoperative parameters were equal for both groups.

The induced spherical aberration post excimer laser ablation can potentially lead to various night vision symptoms and a generalized decrease in visual quality as measured by contrast sensitivity  The use of the OATz treatment algorithms for excimer laser addresses this issue by reducing the induced curvature gradient and increasing the effective optical zone postoperatively. With conventional excimer laser refractive surgery, induced spherical aberration and small effective optical zones are major risk factors for night vision symptoms. Some advocate the use of larger optical zones to circumvent this problem. However this involves increased tissue removal with the risk of ectasia. Additionally, the increased light scatter due to the greater tissue removal may in itself produce disturbing visual phenomena.

The group found that postoperatively, spherical equivalent was similar for both groups. Analysis of the induced wavefront root mean square change was lower for the OATz than the conventional group indicating better optical quality. Corneal topography analysis found that eyes undergoing conventional treatment were more oblate and had smaller effective optical zones. These differences were statistically significant in favor of the OATz group. The increased effective optical zone, less oblate nature and greater optical quality as measured by root mean square is likely to lead to greater visual performance and patient satisfaction in the OATz group. This team reports that indeed the contrast sensitivity performance was better in the OATz cohort compared to the conventional cohort. The better visual performance likely lead to the greater patient satisfaction 3 months postoperatively.

The OPD-CAT software, which corrects all the tiny aberrations, where relevant, has the following results: - 72% better than 6/5, 100% better than 6/6 (20/20), 100% within 0.5 D, 94% within 0.25 D. 

This compares well with other laser systems (all done on low myopes ) Alcon (70% better than 6/5 and 91% better than 6/6 ), VISX (71% better than 6/5 and 98% better than 6/6) and Technolas (70% 6/5 and 91% better than 6/6 )

The article below is about the CATZ system for very aberrated eyes:

New NAVEX software used to treat highly aberrated eyes
LASIK system combines aberrometry, topography, autorefraction with single measurement.

Software upgrades on the Nidek Advanced Vision Excimer laser system will allow surgeons to treat both corneal and internal aberrations, making it ideal for highly aberrated eyes, according to a surgeon who has worked with the technology outside the United States.

The Nidek Advanced Vision Excimer (NAVEX) system is the first platform to calculate aberrometry, topography and autorefraction with a single exam, according to Nidek, and uses these three measurements to create a customized power map and treatment.

According to Paul J. Dougherty, MD, Nidek plans to submit the customized ablation system for Food and Drug Administration approval in the near future. It is currently available in Asia, Europe, South America, Canada and Mexico.

The NAVEX system combines three integrated components: the Optical Path Difference (OPD) Scan, the Final Fit software and the Nidek EC-5000 CX2 laser.

Unique software

Unlike other refractive diagnostic systems, the OPD-Scan uses time-based aberrometry to send 1,440 points of infrared light into the eye and measures the length of time until they return, according to Dr. Dougherty. Traditional Shack-Hartmann aberrometry tracks the positional displacement of only 200 points of visible light sent into the eye.

Currently available modalities, therefore, “have a lot of difficulty with highly aberrated eyes, or getting any scan with highly aberrated eyes,” Dr. Dougherty said. “[The NAVEX system provides] better data because we’re not only treating aberrometry, we’re also treating topography.”

The Final Fit software interfaces with both the OPD-Scan and the laser to analyse the power and wavefront map and creates a custom treatment algorithm for each patient.

“Final Fit breaks the treatment down into a spherical component, a cylinder component and an irregularity component,” Dr. Dougherty said. “And with the Final Fit software you can specify … that it treat only the irregularity component, because in highly aberrated eyes, often any refractive error you find is directly related to irregularity as opposed to true sphere and cylinder.”

Several options

Surgeons can select one of three software options with the NAVEX system. For primary eyes and enhancements, OATz (Optimized Aspheric Treatment Zone) is a topography-based treatment that maintains corneal asphericity and allows for large optical zones. Dr. Dougherty described the OATz mode as an ablation profile that decreases aberrations at the level of the transition zone.

Highly aberrated eyes, meanwhile, might benefit from CATz (Customized Aspheric Treatment Zone) mode or OPDCAT mode, the newest software option, he said.

While CATz treats corneal aberrations, OPDCAT treats both corneal and internal higher-order aberrations, according to Dr. Dougherty. “It gives a true aspheric optical zone and transition zone, and ultimately this software will be able to treat both primary and highly aberrated eyes,” he said.

Case study

Dr. Dougherty recalled the case of a male patient in his 50s who had a deep keratectomy due to a previous keratome malfunction. The incision required suturing two times.

The patient had undergone two PRKs with mitomycin but was left with significant astigmatism and best corrected visual acuity of 20/40. He also had significant horizontal coma in the area of the keratectomy, Dr. Dougherty said.

“The current aberrometry-based treatments I don’t think would have given me the results that I wanted,” he said. He instead referred the patient out of the country for treatment with the NAVEX system.

One month after undergoing CATz PRK with mitomycin, the patient had improved to 20/25 uncorrected vision with significantly improved topography, Dr. Dougherty reported.

“One of the great things about the Nidek laser – and I kind of look at the Nidek laser as a Ferrari as opposed to a Chevrolet – is that you can adjust so many of the treatment parameters for the patient,” he said. “So with the Final Fit software, you can specifically change optical zones and transition zones.”

Ease of use

The laser itself is also easy to use, Dr. Dougherty said.

The EC-5000 CX2 has a 200 Hz video-based active and passive tracker with a cyclotorsion module to detect torsion errors, he said. “One of the great things about this tracker is that there’s no dilation required, and you can basically move instruments through the field without having to reset the tracker.”

Study results

In a study of 132 eyes in Mexico and Canada, 99% of patients achieved within 1 D of intended refraction, and 92% within 0.5 D, he said.

“What’s great about this study, unlike some of the other FDA studies, is that there’s been no pre-selection of patients,” Dr. Dougherty said. “So this study is more indicative of what LASIK would be in a typical refractive centre.”

Patients were treated for up to –8.25 D of sphere and 3 D of cylinder. All patients achieved at least 20/40 vision within 1 month, and 85% achieved at least 20/20. In addition, 27% of patients had visual acuity of 20/15 or better at month 1.

In terms of BCVA, 37% of patients gained one or more lines and no patients lost more than one line. Dr. Dougherty noted that 8.5% of patients lost one line of vision, but there were no other significant complications.

Higher spherical, coma and trefoil aberrations also decreased on average, he said.