Journal of Refractive Surgery

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Wavefront-guided LASIK With the NIDEK NAVEX Platform for the Correction of Myopia and Myopic Astigmatism With 6-month Follow-up

Jan Venter, MD

Abstract

ABSTRACT

PURPOSE: To assess safety, efficacy, predictability, stability, and change in higher order aberrations after wavefront-guided LASIK for myopia and myopic astigmatism using the NIDEK NAVEX platform.

METHODS: Wavefront-guided LASIK was performed in 93 eyes in a 6-month trial with a goal of emmetropia. Treated eyes had a mean subjective manifest spherical equivalent refraction of -4.08±1.99 D diopters (D), with a range of -9.50 to -0.38 D of myopia and -4.50 to 0.00 D of astigmatism. An early nomogram with the OPDCAT software program provided by the manufacturer was used in all procedures. Safety, efficacy, predictability, stability, and change in higher order aberrations were evaluated at 6 months.

RESULTS: At 6 months, 100% eyes were within ±1.0 D of emmetropia and 95% eyes were within ±0.5 D. Uncorrected visual acuity (UCVA) of ≥1.0 was achieved in 89% of eyes, and 38% of eyes achieved UVCA of ≥1.2. No eyes lost ≥2 lines of best spectacle-corrected visual acuity (BSCVA), 25% of eyes gained 1 line, 3% gained 2 lines, and 1% gained ≥2 lines of BSCVA. Higher order root-mean-square (RMS) values increased by 19% on average between pre- and postoperative measurements. Eyes treated with higher order aberrations of <0.3 RMS showed on average an increase of 40% on preoperative values, whereas eyes with significant aberrations showed a decrease in aberrations following wavefront treatment.

CONCLUSIONS: Wavefront-guided ablation using the NIDEK NAVEX platform is safe, effective, and predictable. However, patients with low amounts of aberrations showed an increase in aberrations following wavefront treatment, therefore, wavefront treatment may not be indicated or beneficial to every patient. [J Refract Surg. 2005;21(Suppl):S640-S645.]

Abstract

ABSTRACT

PURPOSE: To assess safety, efficacy, predictability, stability, and change in higher order aberrations after wavefront-guided LASIK for myopia and myopic astigmatism using the NIDEK NAVEX platform.

METHODS: Wavefront-guided LASIK was performed in 93 eyes in a 6-month trial with a goal of emmetropia. Treated eyes had a mean subjective manifest spherical equivalent refraction of -4.08±1.99 D diopters (D), with a range of -9.50 to -0.38 D of myopia and -4.50 to 0.00 D of astigmatism. An early nomogram with the OPDCAT software program provided by the manufacturer was used in all procedures. Safety, efficacy, predictability, stability, and change in higher order aberrations were evaluated at 6 months.

RESULTS: At 6 months, 100% eyes were within ±1.0 D of emmetropia and 95% eyes were within ±0.5 D. Uncorrected visual acuity (UCVA) of ≥1.0 was achieved in 89% of eyes, and 38% of eyes achieved UVCA of ≥1.2. No eyes lost ≥2 lines of best spectacle-corrected visual acuity (BSCVA), 25% of eyes gained 1 line, 3% gained 2 lines, and 1% gained ≥2 lines of BSCVA. Higher order root-mean-square (RMS) values increased by 19% on average between pre- and postoperative measurements. Eyes treated with higher order aberrations of <0.3 RMS showed on average an increase of 40% on preoperative values, whereas eyes with significant aberrations showed a decrease in aberrations following wavefront treatment.

CONCLUSIONS: Wavefront-guided ablation using the NIDEK NAVEX platform is safe, effective, and predictable. However, patients with low amounts of aberrations showed an increase in aberrations following wavefront treatment, therefore, wavefront treatment may not be indicated or beneficial to every patient. [J Refract Surg. 2005;21(Suppl):S640-S645.]

Laser in situ keratomileusis (LASIK), initially reported by Pallikaris et al,1 is the most widely used refractive procedure in the world, and researchers have reported relatively good results.2-9 However, some problems with LASIK have been identified. One is that the ablation may decrease visual function, especially contrast sensitivity, in eyes with high myopia.10,11 One possible reason for the decrease is that "standard LASIK" corrects spherical and regular astigmatic errors but does not correct higher order optical aberrations. To solve this problem, wavefront-guided LASIK has been proposed. Wavefront-guided LASIK aims to correct higher order aberrations as well as irregular astigmatism using preoperative wavefront analysis12-14 to determine the individual ablation pattern.

Several studies have reported the results of wavefront-guided LASIK.15-18 We report 6-month clinical outcomes using the NIDEK NAVEX platform.

PATIENTS AND METHODS

Ninety-three eyes of 56 patients underwent wavefront-guided LASIK for emmetropia between September 2004 and December 2004 at Optimax Laser Eye Specialists, London, United Kingdom, and were followed for at least 6 months. Written informed consent was obtained from all patients. Of the 56 patients, 62% were women and 38% were men with an average age of 36 years (range: 24 to 61 years). The mean manifest spherical equivalent refraction was -4.08±1.99 D (range: -9.50 to -0.38 D) preoperatively.

The following examinations were performed preoperatively in all patients (the same as those for standard LASIK): slit-lamp examination of the anterior segment, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest subjective and objective refractions with the autorefractor/autokeratometer (ARK-9000S; NIDEK, Gamagori, Japan), cycloplegic subjective and objective refractions with instillation of cyclopentolate hydrochloride, intraocular pressure (NIDEK NT-2000 noncontact tonometer), corneal thickness with ultrasound pachymetry (SP-2000; Tomey Corp, Nagoya, Japan), ophthalmoscopy, and corneal topography (NIDEK OPD-Scan).

Preoperative examination was performed with the NIDEK OPD-Scan for wavefront-guided LASIK. Wavefront analysis with OPD-Scan uses dynamic skiascopy technology and Placido disk corneal topography. The results were linked with the Final Fit software to determine the individual ablation pattern using the OPD-CAT software program and directly transferred to the NIDEK EC-5000 CXII excimer laser.

Aberration data with OPD-Scan were obtained and adopted as follows. First, aberrations were measured with and without dilation. Aberrations with dilation were measured 5 to 10 minutes after instillation of tropicamide 0.4% eye drops. To adopt one set of values for surgery, the obtained data were eliminated if the treatment zone could not be filled due to insufficient pupil diameter. The OPD-Scan measures aberrations and also calculates the refraction based on each measurement. The aberration values were used for surgery when the calculated refraction was close to the eye's non-dilated manifest refraction.

The maximum ablation depth was calculated with ultrasound pachymetry. The maximum ablation depth was the corneal thickness minus the planned flap thickness (130 µm) using a minimum residual bed thickness of 250 µm. All eyes were treated with a 5-mm optical zone and 8.5-mm transition zone.

All patients were treated by the same surgeon. After the eye was topically anesthetized with proxymetacaine hydrochloride 0.5%, the surgical field was disinfected by povidone-iodine and draped with a SteriDrape (3M, St Paul, Minn). A speculum was placed and the cornea marked.

After a 130-µm flap was created with the NIDEK MK-2000 microkeratome, the corneal stroma was ablated by the flying-spot system with 1.0-mm spots to treat irregularity (higher order aberrations) and a scanning slit to treat myopic and astigmatic component, and an active eye tracker with a 200 Hz tracking rate. The flap was aligned. The flap and stromal bed were washed with a balanced salt solution, and the flap was dried for approximately 1 minute.

Postoperatively, patients were instructed to instill ofloxacin 0.3%, fluorometholone 0.1%, and sodium hyaluronate 0.3% without preservatives on the day of surgery and to continue for 2 weeks. On postoperative day 1, 1 week, and 1,3, and 6 months, slit-lamp examination of the anterior segment, UCVA, BSCVA, manifest subjective and objective refractions, and corneal topography were performed.

Table

TABLEPre- and Postoperative Manifest Refractions of 93 Eyes That Underwent Wavefront-guided LASIK for the Correction of Myopia and Myopic Astigmatism

TABLE

Pre- and Postoperative Manifest Refractions of 93 Eyes That Underwent Wavefront-guided LASIK for the Correction of Myopia and Myopic Astigmatism

The clinical outcomes of wavefront-guided LASIK were evaluated based on standard formats and criteria19,20 for safety, efficacy, predictability, stability, complications, and pre- and postoperative aberrations. For analysis of visual acuity data, decimal values were converted to logMAR equivalents.21

Safety and efficacy indices19 are defined as the mean postoperative BSCV A/mean preoperative BSCVA and the mean postoperative UCV A/mean preoperative BSCVA, respectively.

RESULTS

The pre- and postoperative mean manifest refractions are shown in the Table.

Safety was evaluated by the BSCVA. The change in BSCVA from preoperatively to 6 months postoperatively is summarized in Figure 1. Of the eyes, 59% had no change in BSCVA, and 29% gained ≥ line.

The change in UCVA is shown in Figure 2. The mean UCVA was 0.04 preoperatively and 1.11 at 6 months. The efficacy index was 1.13 (ie, 1.18/1.44). Figure 3 shows the preoperative BSCVA and the postoperative achieved UCVA.

Figure 4 shows the attempted and achieved amounts of correction. Figure 5 shows refractive outcome as the percentage of eyes that were within ±2.0 D, ±1.0 D, and ±0.5 D of the intended spherical equivalent refraction.

Stability is shown as the change in the subjective refraction (Fig 6).

No complication such as epithelial ingrowth, diffuse lamellar keratitis, or infection was observed.

Figure 1. Changes in BSCVA from preoperatively to 6 months postoperatively in 93 eyes after LASIK? 59% of eyes had no change in BSCVA and 29% gained ≥1 line.Figure 2. Postoperative UCVA. The mean UCVA was 0.04 preoperatively and 1.11 at 6 months.Figure 3. Uncorrected visual acuity at 6 months.

Figure 1. Changes in BSCVA from preoperatively to 6 months postoperatively in 93 eyes after LASIK? 59% of eyes had no change in BSCVA and 29% gained ≥1 line.

Figure 2. Postoperative UCVA. The mean UCVA was 0.04 preoperatively and 1.11 at 6 months.

Figure 3. Uncorrected visual acuity at 6 months.

Figure 4. Predictability. The spherical equivnt refractions are shown on the x-axis, achieved myopic corrections on the y-axis, and predictabilities of ±1.0 D in the lines.Figure 5. Refractive outcome of 93 eyes 6 months after LASIK.

Figure 4. Predictability. The spherical equivnt refractions are shown on the x-axis, achieved myopic corrections on the y-axis, and predictabilities of ±1.0 D in the lines.

Figure 5. Refractive outcome of 93 eyes 6 months after LASIK.

Figure 7 shows the pre- and postoperative higher order aberrations. A 19% increase in RMS higher order aberrations was noted between pre- and postoperatively.

In Figure 8, the pre- and postoperative aberrations are compared by dividing the eyes into two groups ? eyes with RMS value <0.3 and eyes with RMS value >0.3. In the group treated with RMS values <0.3, a 40% increase in total higher order aberrations was noted. The group with higher order aberrations >0.3 showed an 18% decrease following wavefront treatment.

DISCUSSION

In refractive surgery, safety is of primary importance. The safety index in this study was 1.16, 29% of eyes gained ≥ line of BSCVA, and no eye lost ≥2 lines. Safety of LASIK with the NIDEK NAVEX laser system is high. Nuijts et al22 performed wavefrontguided LASIK for low to moderate myopia in 12 cases with a mean manifest spherical equivalent refraction of -3.88±1.92 D. Their safety index was 1.12, which is significantly higher than their results with standard LASIK. Our study achieved an excellent result with moderate to high myopia of -4.08±1.99 D (mean manifest spherical equivalent refraction).

With current technology, it is difficult to correct small degrees of higher order aberrations. In comparing pre- to postoperative data, eyes that had very little higher order aberrations to begin with ended up with an increase in higher order aberrations. When eyes with <0.3 RMS were treated with wavefront, a 40% increase in the higher order aberrations was measured. However, most patients with significant amounts of higher order aberrations preoperatively end up with less aberration after wavefront. Similar results have been reported by Schallhorn.23

Figure 6. Stability of the refraction in 93 eyes 1, 3, and 6 months after LASIK.Figure 7. Pre- and postoperative higher order aberrations of 93 eyes that underwent LASIK.Figure 8. Preoperative aberrations in the lower RMS group (RMS <0.3) and the higher RMS group (>0.3 RMS) (pxs = patients).

Figure 6. Stability of the refraction in 93 eyes 1, 3, and 6 months after LASIK.

Figure 7. Pre- and postoperative higher order aberrations of 93 eyes that underwent LASIK.

Figure 8. Preoperative aberrations in the lower RMS group (RMS <0.3) and the higher RMS group (>0.3 RMS) (pxs = patients).

Patients with low amounts of higher order aberrations are more likely to have an increased RMS than those patients with high RMS, where the higher order aberrations are likely to decrease with NIDEK NAVEX treatments. Excellent results can be obtained using an aspheric optimized ablation profile. Based on the results of this study, surgeons may consider reserving wavefront ablation for patients with significant higher order aberrations (≥0.3 RMS).

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TABLE

Pre- and Postoperative Manifest Refractions of 93 Eyes That Underwent Wavefront-guided LASIK for the Correction of Myopia and Myopic Astigmatism

10.3928/1081-597X-20050902-17

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