Journal of Refractive Surgery

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Comparison of NIDEK CATz Wavefront-guided LASIK to Traditional LASIK With the NIDEK CXII Excimer Laser in Myopia

Rui He, MB; Min Qu, MM; Shun Yu, MB

Abstract

ABSTRACT

PURPOSE: To compare the visual and refractive outcomes in myopic LASIK between wavefront-guided and traditional treatment.

METHODS: The study included 162 eyes of 81 myopic patients undergoing LASIK by one surgeon. The right eye of each patient underwent customized LASIK with the NIDEK NAVEX laser system (NIDEK, Gamagori, Japan) (study group); the left eye of each patient underwent traditional LASIK with the NIDEK CXII excimer laser system (control group).

RESULTS: No significant differences were noted in refractive error, uncorrected visual acuity, and best spectacle-corrected visual acuity after surgery between the two groups (t test, P > .05). Postoperatively, 3.7% of patients in the study group reported glare, which was significantly lower than 12.4% in the control group (chi-square test, .01 < P < .05). Higher order aberrations increased after surgery in both groups, but less increase was noted in patients in the study group. A statistically significant reduction was noted in the postoperative increase of Zernike coefficients C7, C8, and C12 in the study group compared to the control group (t test, P < .05).

CONCLUSIONS: Customized LASIK significantly reduces the rate of postoperative glare and induction of higher order aberrations compared to traditional LASIK. [J Refract Surg. 2005;21(Suppl):S646-S649.]

Abstract

ABSTRACT

PURPOSE: To compare the visual and refractive outcomes in myopic LASIK between wavefront-guided and traditional treatment.

METHODS: The study included 162 eyes of 81 myopic patients undergoing LASIK by one surgeon. The right eye of each patient underwent customized LASIK with the NIDEK NAVEX laser system (NIDEK, Gamagori, Japan) (study group); the left eye of each patient underwent traditional LASIK with the NIDEK CXII excimer laser system (control group).

RESULTS: No significant differences were noted in refractive error, uncorrected visual acuity, and best spectacle-corrected visual acuity after surgery between the two groups (t test, P > .05). Postoperatively, 3.7% of patients in the study group reported glare, which was significantly lower than 12.4% in the control group (chi-square test, .01 < P < .05). Higher order aberrations increased after surgery in both groups, but less increase was noted in patients in the study group. A statistically significant reduction was noted in the postoperative increase of Zernike coefficients C7, C8, and C12 in the study group compared to the control group (t test, P < .05).

CONCLUSIONS: Customized LASIK significantly reduces the rate of postoperative glare and induction of higher order aberrations compared to traditional LASIK. [J Refract Surg. 2005;21(Suppl):S646-S649.]

Multiple studies have shown that traditional LASIK is effective and safe for the correction of myopia. Traditional LASIK is limited by the fact that it only targets lower order aberrations. As a result, issues with the degradation of visual quality, such as glare and the decrease in night vision, can occur postoperatively.1,2 It has been reported that wavefront-guided LASIK can potentially reduce issues with degradation of visual quality by targeting higher order aberrations in addition to the lower order aberrations.3"5 We used the NIDEK NAVEX customized ablation system (NIDEK, Gamagori, Japan) to treat myopia and compared the results with traditional LASIK with the NIDEK CXII excimer laser system.

PATIENTS AND METHODS

The study comprised 162 eyes of 81 patients (42 women and 39 men) that underwent myopic LASIK between October 2003 and January 2004. Patient age ranged from 18 to 38 years (mean: 25.9?4.7 years). Preoperative spherical equivalent refraction in right eyes (study group, n=81) and left eyes (control group, n=81) ranged from -2.25 to -12.50 diopters (D) (-6.76±2.89 D) and -2.75 to -11.75 D (-7.20±2.12 D), respectively. The astigmatism ranged from -3.25 to 0.0 D (-0.88±0.87 D) in the study group and -2.75 to 0.0 D (-0.92±0.81 D) in the control group. Best spectaclecorrected visual acuity (BSCVA) was >0.6, and no ocular disease was found preoperatively in any eye.

Preoperative measurements included corrected and uncorrected distance and near visual acuity, non-contact eye pressure, corneal pachymetry, manifest and cycloplegic refraction, corneal topography, and wavefront aberrometry. Visual acuity, refractive error, and wavefront aberrations were measured 1 week and 1,3, and 6 months after surgery. Patients were also asked whether they experienced glare. Subjective glare was quantified according to the patient's answer (yes or no).

Table

TABLE 1Pre- and Postoperative Refraction (Mean±Standard Deviation, D) in 162 Eyes That Underwent Wavefront-guided or Traditional LASIK

TABLE 1

Pre- and Postoperative Refraction (Mean±Standard Deviation, D) in 162 Eyes That Underwent Wavefront-guided or Traditional LASIK

Wavefront aberrations were evaluated using the NIDEK OPD-Scan. The NIDEK OPD-Scan is a combination aberrometer, topographer, autorefractor, and autokeratometer. The measurement is conducted in a dark room without dilating the patient. This timebased aberrometry is performed using a technique called dynamic skiascopy that measures time differences from 1440 points of infrared light projected into the eye and reflected by the retina.

The NIDEK EC-5000 CXII excimer laser system and Moria M2 automated microkeratome (Moria, Antony, France) were used in surgery. All surgeries were performed by one surgeon (R.H.). Wavefront data obtained by the OPD-Scan system were analyzed by Final Fit software using the Customized Aspheric Treatment zone (CATz) program. Customized ablation data were produced and imported into the EC-5000 CXII excimer laser system. Before surgery, the ablation depth and effective optical zones were calculated according to pupil size by simulating surgical results. The diameters of ablation and transition zone were 3.5 to 4.0 mm and 7.5 to 8.0 mm, respectively, in the study group, and 5.0 to 5.5 mm and 7.0 to 7.5 mm, respectively, in the control group. The thickness of hinged corneal flaps ranged from 70 to 130 µm and the calculated residual stromal thickness was >250 µm in all cases.

Statistical analysis was performed with t testing and chi-square testing for quantitative and qualitative data, respectively.

RESULTS

VISUAL ACUITY

The mean BSCVA before surgery was 0.99±0.13 for the study group and 0.98±0.14 for the control group. The mean uncorrected visual acuity (UCVA) after surgery was 1.04±0.18 for the study group and 1.07±0.20 for the control group. No eyes lost ≥1 line of BSCVA. Of the study and control eyes, 42.5% and 40%, respectively, had improvement in their BSCVA by at least 1 line after surgery. This small difference was not statistically significant (P>.05).

REFRACTIVE ERROR

The data summarizing mean refractive error in each group before and after surgery are shown in Table 1. No significant difference was found between the two groups pre- or postoperatively (P>.05).

GLARE

Three (3.7%) eyes in the study group and 10 (12.4%) eyes in the control group reported subjective glare 6 months after surgery. This difference was statistically significant (chi square=4.10; .01<P<.05).

HIGHER ORDER ABERRATIONS

The root-mean-square (RMS) value of higher order aberrations measured at a 6-mm pupil size increased after surgery in both groups, but the eyes in the study group had significantly less increase in the RMS value than the control group (P<.01) at each time interval after surgery (Table 2). The study group had significantly lower postoperative Zernike coefficients C7, C8, and C12 compared to the control group (f test, P<.05) (Fig).

DISCUSSION

Traditional LASIK has been shown to be an effective surgery to treat myopia and astigmatism, but may be limited by decreased visual quality. Many researchers have shown that this degradation of visual quality is the result of an increase in higher order aberrations.1,2,6 The goal of wavefront-guided excimer laser surgery is to minimize the induction of, and possibly reduce, higher order aberrations, thereby improving visual quality in addition to achieving better Snellen visual acuity.

Higher order aberrations can be measured by current wavefront technology. With the development of flying spot lasers and eye-tracking systems, it is possible to treat higher order aberrations. The NAVEX system can perform wavefront-guided aspheric ablations using a combination of scanning slit and flying spot technology. NAVEX is composed of the OPD-Scan, Final Fit software, and EC-5000 CXII excimer laser system. The data from OPD-Scan are imported into Final Fit software. In this study, the CATz software program was used to analyze, design, and calculate the ablation shape. Final Fit software compares the target topographic map with the preoperative map, creating an ablation profile that separates the treatment into spherical, cylindrical, and irregularity components.

Table

TABLE 2RMS of Pre- and Postoperative Higher Order Aberrations (Mean±Standard Deviation, µm) in 162 Eyes That Underwent Wavefront-guided and Traditional LASIKFigure. Zernike coefficients A) before surgery, B) 1 month after surgery, C) 3 months after surgery, and D) 6 months after surgery.

TABLE 2

RMS of Pre- and Postoperative Higher Order Aberrations (Mean±Standard Deviation, µm) in 162 Eyes That Underwent Wavefront-guided and Traditional LASIK

Figure. Zernike coefficients A) before surgery, B) 1 month after surgery, C) 3 months after surgery, and D) 6 months after surgery.

Our results showed that the NIDEK NAVEX CATz ablation has advantages in improving visual quality over traditional LASIK. No significant difference was noted in UCVA or BSCVA after surgery between the two groups. However, a statistically significant decrease was found in glare complaints and induction of higher order aberrations in the customized LASIK group compared to the traditional LASIK group.

The normal corneal shape is aspheric with the center more curved than the periphery. This shape minimizes the amount of spherical aberration. After traditional refractive surgery, the peripheral curvature becomes steeper compared with the center, causing spherical aberration to increase.7 CATz customized ablations help reshape the transition zone and maintain an aspheric corneal surface after ablation. The transition zone reduces the difference between central curvature and peripheral curvature; this smooth change decreases the induction of spherical aberration (C12) after surgery in customized treatments compared to traditional treatments.

Spherical aberration and coma are the Zernike coefficients that are most strongly correlated with postoperative glare. The decreased induction in Zernike coefficients C7, C8, and C12 after customized LASIK compared to traditional LASIK explains why patients who had customized LASIK might have fewer night vision complaints than patients who had traditional LASIK.

Some studies have shown that larger ablation diameters can reduce the occurrence of glare and the deterioration of night vision. However, ablation depth is increased with larger ablation diameter. In comparing customized LASIK to traditional LASIK, we found no statistically significant difference in ablation depth despite the fact that ablation diameter was 0.5 to 1.0 mm larger in customized LASIK. For example, when treating 6.00 D of myopia, the ablation depths in customized LASIK and traditional LASIK in this study were 89.4 µm and 90.0 µm, respectively.

Our results showed no significant difference in UCVA between customized LASIK and traditional LASIK.

Customized LASIK was no more likely to create supervision than traditional LASIK. Customized LASIK can achieve satisfactory surgical results but does not routinely result in supervision. The probable reason for this is that the exact relationship between every component of wavefront aberration, Snellen visual acuity, and ablation pattern is not well defined.

Traditional LASIK can correct lower order aberrations efficiently. The NIDEK NAVEX customized ablation system with the CATz program has advantages in minimizing the postoperative induction of higher order aberrations and minimizing glare symptoms compared to traditional treatments.

REFERENCES

1. Martinez CE, Applegate RA, Klyce SD, McDonald MB, Medina JP, Howland HC. Effect of pupillary dilation on corneal optical aberrations after photorefractive keratectomy. Arch Ophthalmol. 1998;116:1053-1062.

2. Oshika T, Klyce SD, Applegate RA, Howland HC, El Danasoury MA. Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis. Am J Ophthalmol. 1999;127:1-7.

3. Mrochen M, Kaemmerer M, Seiler T. Clinic results of wavefront-guided laser in situ keratomileusis 3 months after surgery. J Cataract Refract Surg. 2001;27:201-207.

4. Wang Z, Yang B, Zhang C, Huang GF, Chen JQ. Wavefront-guided laser in situ keratomileusis for myopia [Chinese]. Zhonghua Yan Ke Za Zhi. 2004;40:9-12.

5. Mrochen M, Kaemmerer M, Seiler T. Clinical results of wavefront-guided laser in situ keratomileusis 3 months after surgery. J Cataract Refract Surg. 2001;27:201-207.

6. Seiler T, Kaemmerer M, Mierdel P, Krinke HE. Ocular optical aberrations after photorefractive keratectomy for myopia and myopic astigmatism. Arch Ophthalmol. 2000;118:17-21.

7. Jin H, Wang Q, Wang D, et al. The change of aberration after LASIK. China Ophthalmol Res. 2004;22:183-186.

TABLE 1

Pre- and Postoperative Refraction (Mean±Standard Deviation, D) in 162 Eyes That Underwent Wavefront-guided or Traditional LASIK

TABLE 2

RMS of Pre- and Postoperative Higher Order Aberrations (Mean±Standard Deviation, µm) in 162 Eyes That Underwent Wavefront-guided and Traditional LASIK

Figure. Zernike coefficients A) before surgery, B) 1 month after surgery, C) 3 months after surgery, and D) 6 months after surgery.

10.3928/1081-597X-20050902-18

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