Customized excimer laser ablations using laser in situ keratomileusis (LASIK) or photorefractive keratectomy can be based on corneal topography, whole-eye wavefront, or corneal wavefront. Topography-based ablations treat irregularities in corneal elevation in addition to the spherocylindrical refractive error.Wavefront-based treatments address the wavefront aberrations of the cornea or the entire eye in addition to the refractive error. A number of studies have demonstrated that topography-based ablations are safe and effective in the treatment of primary myopia and astigmatism. ^1–9

Custom ablation, whether topography-based or ocular wavefront-based, has been developed to address some of the disadvantages of conventional spherocylindrical ablation. The unoperated, normal cornea is prolate with an average positive asphericity of approximately +0.24. Conventional myopic ablations create an oblate cornea, increasing corneal asphericity and inducing positive spherical aberration, which can cause bothersome mesopic and scotopic symptoms such as glare and halos and difficulty driving.^10–12

Topography-guided treatments have advantages over wavefront-guided treatments: (1) topographers can measure a wider area on the cornea than aberrometers, (2) topographers can accurately measure highly aberrated eyes, and (3) topographers have a higher number of data points than aberrometers.

A disadvantage of topography-based treatments is that they do not incorporate all of the refracting elements of the eye into the treatment, which leads to a decoupling of lenticular and corneal aberrations and may alter visual quality postoperatively. Corneal and lenticular spherical aberrations compensate for each other in the normal myopic eye up to approximately age 30.¹³ Therefore, treating only the corneal spherical aberration may unmask lenticular spherical aberrations, which could cause halos at night.¹³ One ablation strategy that may reduce this unmasking is the use of aspheric treatment zones that attempt to induce less change in corneal curvature and less spherical aberration.

The customized aspheric treatment zone (CATz) ablation of the NIDEK CXII excimer laser employs aspheric treatment zones. The CATz ablation architecture uses a combination of optical and transition zones, which gradually taper the corneal curvature paracentrally and peripherally, creating a single treatment zone, as defined by Hori-Komai and colleagues.¹⁴ The aspheric transition zone has been referred to as optimized aspheric transition zone (OATz). In CATz, this aspheric ablation is combined with the treatment of corneal elevation irregularities.

The current study evaluated the efficacy, predictability, safety, wavefront induction, and patient satisfaction of LASIK to correct low to moderate myopia with astigmatism using the customized aspheric treatment zone algorithm of the Nidek CXIII excimer laser in an ongoing US Food and Drug Administration (FDA) trial.

One hundred thirty-five eyes of 68 patients (1 patient was treated unilaterally) were treated with LASIK for myopia with astigmatism. The average age was 36 ± 11.2 years (range, 23–64 years). All patients included in the study were 21 years of age or older and had spherical manifest refractive error ranging from −0.50 to −7.00 D with 0.50 D to 4.00 D of astigmatism. Patients were enrolled in the study if they had a stable refraction for 1 year prior to the study and discontinued contact lenses for at least 3 days to 28 days (depending on contact lens type) prior to preoperative examination in order to stabilize keratometry and corneal topography. Patients were required to have normal keratometry and topography with less than 10 μm of corneal irregularity as determined by the OPD-Scan. (NIDEK Co Ltd, Gamagori, Japan). Patients who had an acute illness, a calculated postoperative corneal bed thickness less than 250 μm after ablation, preoperative central corneal thickness of less than 475 μm, any prior ophthalmic surgery, or abnormal corneal topography were excluded from the study.

Preoperatively, the mean manifest refraction spherical equivalent (MRSE) was −3.57 ± 1.45 D, the mean sphere was −3.06 ± 1.39 D, and the mean cylinder was −1.02 ± 0.64 D. Preoperative ophthalmic examination included distance uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), MRSE, slit-lamp examination, corneal topography and aberrometry (6-mm pupil) using the OPD-Scan, pupillometry using the OPD-scan, ultrasound pachymetry (instruments varied by site), keratometry, and a dilated fundus examination by the surgeon. The same measurements (with the exception of dilated funduscopy and pupillometry unless warranted) were performed at 1 week, 1 month, 3 months, and 6 months postoperatively.

The quality of vision was assessed using the validated Refractive Status and Vision Profile (RSVP)¹⁵ and a questionnaire that was designed for the specific needs of this study. This questionnaire was a 10-point self- administered questionnaire. Patients were asked to rate the presence or absence of each visual complaint in their CATz-treated eye(s) at baseline before the CATz-guided LASIK treatment and at each postoperative visit, beginning at month 1. Subjects were instructed to rate the absence of a complaint as “none” and the presence of a complaint as “mild,” “moderate,” “marked,” or “severe.”

CATz differs from a conventional spherocylindrical ablation in that the treatment area that lies between the outer edge of the optical zone (OZ) and the outermost area of the entire ablation zone is adjustable, based on the diameter of the OZ and transition zone (TZ) that are selected. In the transition zone, the volume of ablation gradually decreases as the ablation expands peripherally to minimize changes in corneal curvature. The use of an OZ with the TZ architecture described above is called OATz (optimized aspheric treatment zone),¹⁴ and the treatment of corneal surface irregularities in addition to OATz is called CATz. The Nidek EC5000 CXIII offers 7 different profiles for the transition zone, and the OATz profile No. 5 was used for all treatments. All eyes were targeted for emmetropia with sphere and cylinder values based on the preoperative manifest refraction. The corneal irregularity simulated in Final Fit could not exceed an elevation of 10 μm. Based on previous experience, 80% of the calculated irregularity treatment was selected, of which 50% was actually programmed for treatment. This conservative calculation prevented overtreatment in eyes with prominent irregularity.

In this study all eyes underwent the refractive treatment using a 5.00-mm-diameter optical zone and an 8.50-mm transition zone. Corneal surface irregularities were treated using a 6.00-mm OZ and an 8.50-mm TZ for all eyes. The combination of optical and transition zones and the irregularity ablation constituted the total treatment zone and created the refractive correction of the eye. The sphere and cylinder input values were not modified according to the magnitude or pattern of corneal irregularity. A satisfactory simulated result was one in which the corneal topography minimized the gradient of corneal curvature change, maximized the effective optical zone, and reduced or eliminated the corneal irregularities, yet maintained adequate residual corneal tissue in the stromal bed. The surgeon, NIDEK engineer, and Clinical Research Consultants staff all reviewed and agreed on the final ablation pattern prior to treatment.

Proper alignment of the eye with the laser was achieved with a 200-Hz infrared eye tracker built into the laser console and centered on the pupil. Torsional errors were corrected by enabling the torsion error detection function of the laser prior to the ablation for improved registration. The flap was lifted, and the excimer laser ablation was delivered to the stoma. Patients fixated on a red fixation light, coaxial with the surgeon’s line of sight and the excimer laser beam, throughout the ablation, allowing the tracker to remain centered on the pupil. The flap was repositioned, and the interface was irrigated with balanced saline solution, removing any debris. Patients received topical fluoroquinolone antibiotic and corticosteroid drops 4 times per day for 5 days.

The mean MRSE for the entire cohort was 0.00 ± 0.38 D at 1 week, −0.04 ± 0.31 D at 1 month, −0.06 ± 0.29 D at 3 months, and −0.09 ± 0.31 D at 6 months. The mean postoperative sphere was 0.11 ± 0.39 D at 1 week, −0.07 ± 0.31 D at 1 month, 0.04 ± 0.32 D at 3 months, and 0.06 ± 0.31 D at 6 months. The mean postoperative manifest refractive cylinder was −0.21 ± 0.27 D at 1 week, −0.23 ± 0.25 D at 1 month, −0.22 ± 0.26 D at 3 months, and −0.25 ± 0.27 D at 6 months. For the entire cohort of 133 eyes, 116 eyes (87.20%) had a MRSE refraction within ±0.50 D, and 131 of 133 eyes (98.5%) were within ±1 D at 1 week. At 1 month, 126 of 135 eyes (93.30%) were within ±0.50 D and all eyes were within ±1 D. At 3 months, 117 of 127 eyes (92.10%) were within ±0.50 D and all eyes were within ±1 D. Of 131 eyes, 122 (93.13%) were within ±0.50 D and 130 (99.24%) were within ±1 D at 6 months postoperatively. Six months after surgery, 116 of 131 eyes (88.55%) had UCVA of 20/20 or better (Figure 1).

FIGURE 1 Preoperative best spectacle-corrected visual acuity (BSCVA) compared to 6 months postoperative uncorrected visual acuity (UCVA) after myopic laser in situ keratomileusis using the Nidek topographically guided custom aspheric treatment zone (CATz) algorithm. (more ...)

At 6 months postoperatively, there was a higher percentage of eyes with better UCVA than preoperative BSCVA at the 20/20 or better levels of acuity (Figure 1). Clinically significant loss of BSCVA is considered a loss of 2 or more Snellen lines. Six months after surgery, no eyes lost 2 or more lines of BSCVA (Figure 2). BSCVA increased by 2 or more lines in 21 of 131 eyes (16.03%) 6 months after surgery (Figure 2). Figure 3 plots the attempted vs achieved results for all eyes at 6 months postoperatively. At 6 months postoperatively, 114 of 131 eyes (87%) had a defocus equivalent of 0.50 D or better (Figure 4).

FIGURE 2 Change in best-corrected visual acuity 6 months after myopic laser in situ keratomileusis using the Nidek topographically guided custom aspheric treatment zone (CATz) algorithm. No eyes lost 2 or more lines.

FIGURE 3 Attempted vs achieved manifest refraction spherical equivalent (MRSE) 6 months after myopic laser in situ keratomileusis using the Nidek topographically guided custom aspheric treatment zone (CATz) algorithm. There is a slight trend toward undercorrection. (more ...)

FIGURE 4 Defocus equivalent 6 months after myopic laser in situ keratomileusis using the Nidek topographically guided custom aspheric treatment zone (CATz) algorithm.

Refractive stability postoperatively was evaluated by assessing the percentage of eyes with a change in MRSE of 1.00 D at 3-month intervals, as well as a mean rate of change in MRSE of 0.5 D or less per year (0.04 D per month). There was a mean change in MRSE of −0.03D ± 0.39 D occurring between the first week and 1 month postoperatively. The MRSE changed by −0.02 D from the first month to the third month and by −0.04 D from the third month to 6 months (Figure 5).

FIGURE 5 Change in manifest refraction spherical equivalent from preoperatively to 6 months after myopic laser in situ keratomileusis using the Nidek topographically guided custom aspheric treatment zone (CATz) algorithm. The refraction is stable over 6 months. (more ...)

Mean root-mean-square (RMS) value for the total higher-order aberrations changed from 0.250 ± 0.103 μm preoperatively to 0.290 ± 0.099 μm 6 months postoperatively. The change in RMS for higher-order aberrations was statistically significant (P = .002). Spherical aberration changed from 0.003 ± 0.065 μm preoperatively to 0.056 ± 0.069 μm 6 months postoperatively. The change in spherical aberrations was statistically significant (P = .000). Mean coma changed from 0.107 ± 0.062 μm preoperatively to 0.137 ± 0.088 μm 6 months postoperatively. The change in coma was statistically significant (P = .001).

Table 1 shows the patient satisfaction obtained using the custom-designed questionnaire at 3 months, the point of refractive stability. Table 2 shows the percent change in patient satisfaction from baseline to 3 months.

TABLE 1 RESULTS OF CUSTOM-DESIGNED SELF-ADMINISTERED PATIENT QUESTIONNAIRE RATING VISUAL COMPLAINTS IN 68 PATIENTS WHO UNDERWENT MYOPIC LASIK USING THE NIDEK CATz ALGORITHM*

TABLE 2 PATIENT SATISFACTION AT BASELINE AND 3 MONTHS ACCORDING TO CUSTOM-DESIGNED SELF-ADMINISTERED QUESTIONNAIRE RATING VISUAL COMPLAINTS IN 68 PATIENTS WHO UNDERWENT MYOPIC LASIK USING THE NIDEK CATZ ALGORITHM

In this investigation of LASIK for the treatment of low to moderate myopia with astigmatism using the Nidek CXIII excimer laser with the topographically guided CATz software, all of the refractive and visual acuity outcomes exceeded the FDA criteria at 6 months postoperatively. Safety was demonstrated, with no eyes losing 2 or more lines of BSCVA 6 months after surgery (Figure 3).

The results in this study are consistent with previous studies of topography-guided LASIK treatment of myopia with astigmatism that found it to be safe and effective.^2,3 Two separate studies of CATz with smaller sample sizes yet a larger treatment range than in this study found that no eyes lost 2 or more lines of BSCVA.^2,3 Kermani and colleagues³ found that 90% of the eyes undergoing CATz were within 0.50 D of the intended MRSE, which is similar to results of 93% in this study. Although the outcomes reported in this study surpass FDA criteria for approval, refractive outcomes can be improved with nomogram refinement. The trend toward undercorrection plotted in Figure 3 could be addressed using either revised software in the laser or individual center nomogram calculations.

The outcomes of this study confirm that topography-guided LASIK is a clinically valuable alternative to ocular wavefront–guided treatment of primary myopia and astigmatism. For example, within 6 months after surgery, 89% of the eyes had UCVA of 20/20 or better without correction (Figure 1). Additionally, at 20/16 or better levels, 6-month postoperative UCVA exceeded preoperative BSCVA in over 25% of cases. There was a clinically significant gain of 2 lines or more of BSCVA in 16% of the eyes (Figure 2). Awwad and colleagues¹⁶ treated a similar range of primary myopia as in this study, but used the VISX CustomVue and Alcon CustomCornea wavefront platforms, and found that 89% of eyes saw 20/20 without correction. Similarly, in a prospective, randomized study of the Wavelight and CustomCornea platforms, 80% of eyes achieved UCVA of 20/20.¹⁷ Comparison of our outcomes to the aforementioned studies indicates that the CATz outcomes are equivalent to those reported for wavefront-guided treatments.¹⁸

In this study, an aspheric treatment zone was utilized to treat myopic astigmatism. Use of aspheric treatments reduces the steep changes in corneal curvature, which may reduce the induction of aberrations compared to conventional ablation. In this study, we found a mild increase in total higher-order aberration RMS of 0.04 μm, a mild increase in spherical aberration of 0.053 μm, and a mild but statistically significant increase of 0.03 μm in coma. Analyzing conventional ablations for myopia and myopic astigmatism, with the Nidek CXIII excimer laser, Du and colleagues⁶ reported an increase in RMS of 0.241 μm for ocular higher-order aberrations, an increase of 0.139 μm of spherical aberration, and an increase of 0.183 μm of coma. The outcomes presented by Du and colleagues show a significant increase in higher-order aberrations compared to the values obtained for CATz in our study. Du and colleagues also found a statistically significant increase in higher-order aberrations in conventional ablations compared to CATz treatments.⁶ This reduced induction of higher-order aberrations may allow better visual quality after CATz ablation compared to conventional ablation.

Visual symptoms after CATz treatment were generally mild. Most strikingly, we found a 23% decrease in patients reporting marked to severe difficulties in night driving, and less than 3% of patients reported an increase in moderate to severe mesopic/scotopic symptoms such as halos, glare, or starburst postoperatively (Tables 1 and 2). Using the RSVP questionnaire in patients who underwent conventional ablation, Schein and colleagues¹⁵ found a worsening of scotopic symptoms by an average of 14.5% and driving by 29.5%, although it is unclear if this was specifically night driving. One study¹⁴ found statistically significantly better visual quality after OATz treatments using the Nidek advanced vision excimer (NAVEX) laser platform compared to conventional treatments. The questionnaire results clearly indicate that CATz topography-guided LASIK gave excellent outcomes in terms of quality of vision and patient satisfaction. Contrast sensitivity testing and comparison to a control group would likely help verify the results obtained here.

The apparent use of small optical zones with CATz requires explanation. The optical zone and transition zone are misnomers when referring to CATz treatments because both zones combine to provide the refractive correction and should be referred to as the treatment zone. A small optical zone might be more prone to decentration, but we do not think the risk of decentration with CATz is any higher than the risk with the 6.50-mm optical zone and 7.50-mm transition zone commonly used in conventional treatments with the CXIII in North America, especially since the procedure used a 200-Hz eye tracker.

The 6-month results presented in this study indicate that topography-guided CATz treatment of myopic astigmatism with the Nidek CXIII is safe, gives excellent refractive and visual acuity results, increases higher-order aberrations minimally, maintains preoperative contrast sensitivity, and improves most patient symptoms compared to baseline.

The 6-month results presented in this study indicate that topography-guided CATz treatment of myopic astigmatism (1) is safe, (2) gives excellent refractive and visual acuity results, (3) results in minimal increase in higher-order aberrations, and (4) maintains preoperative contrast sensitivity. However, topography-based treatments have 3 major theoretical limitations: exclusion of the internal aberrations from the treatment (which may lead to decoupling of lenticular and corneal aberrations and may alter postoperative visual quality); arbitrary setting of the postoperative asphericity; and spherical refractive error estimation difficulties.

Although this study was not designed to compare topography-based to wavefront-based customized treatments,¹ topography-guided treatments should be helpful for the correction of postoperative refractive errors.^2,3 This approach would also be useful for patients with preoperative confirmation that aberrations are primarily corneal in origin (with absent lenticular astigmatism).

Financial Disclosures: None.

Funding/Support: None.

Financial Disclosures: Dr Dougherty is a consultant to NIDEK Co, Ltd, and Alcon, Inc. Mr. Bains is a consultant to NIDEK Co, Ltd.

Dr Waring is a consultant to NIDEK Co, Ltd, Advanced Medical Optics, Inc, Acufocus, Inc, Calhoun Vision, Inc, and Schwind. Dr Chayet is a consultant to NIDEK Co, Ltd, and Calhoun Vision, Inc. Dr Fant is a consultant to NIDEK Co, Ltd, and has a financial interest in Clinical Research Consultants Inc. Dr Stevens is a consultant to NIDEK Co, Ltd, and Clinical Research Consultants Inc. Author Contributions: Design and conduct of the study (G.W., H.S.B., B.F., G.S); Collection, management, analysis, and interpretation of the data (G.W., H.S.B, B.F., G.S); Preparation, review, and approval of the manuscript (G.W., P.J.D., H.S.B., J.F., A.C.).