## Purpose

To evaluate the effect of changing the pupil size on the corneal first-surface higher-order aberrations induced by different refractive treatments: standard laser in situ keratomileusis (LASIK), custom LASIK, and corneal refractive therapy.

## Design

Observational study.

## Methods

Eighty-one right eyes from patients with a mean age of 29.94 ± 7.5 years, of which 50 were female (61.7%), were analyzed retrospectively at the Clínica Oftalmológica NovoVision, Madrid, Spain. Corneal videokeratographic data were used to obtain corneal first-surface higher-order aberrations for aperture diameters from 3 to 8 mm using the Vol-CT software (Sarver & Associates, Inc). Total root mean square (RMS) and RMS for third- to sixth-order Zernike polynomials as well as spherical-like, coma-like, secondary astigmatism, and spherical plus coma-like variables were calculated.

## Results

We verified an increase in the higher-order aberration total RMS after treatments of 0.014 ± 0.025 μm, 0.019 ± 0.027 μm, and 0.018 ± 0.031 μm for standard LASIK, custom LASIK, and corneal refractive therapy, respectively, for 3-mm pupil diameter. For the 8-mm aperture diameter, changes in total RMS increased by a factor of 50 compared with the variation for the 3-mm diameter up to 0.744 ± 0.731 μm, 0.493 ± 0.794 μm, and 0.973 ± 1.055 μm for standard LASIK, custom LASIK, and corneal refractive therapy, respectively.

## Conclusions

The 3 techniques increase the wavefront aberrations of the cornea and change the relative contribution of coma-like and spherical-like aberrations. For a large aperture (> 5 mm), corneal refractive therapy induces more spherical-like aberrations than standard and custom LASIK. However, no clinically or statistically significant differences existed for narrower apertures. Standard and custom LASIK did not display statistically significant differences regarding higher-order aberrations.

Laser in situ keratomileusis (LASIK) and corneal refractive therapy (CRT) for orthokeratology are 2 techniques that attempt a certain independence from conventional compensation by spectacles or traditional contact lenses. Both of these techniques use a similar principle to correct myopia, which is making the central corneal surface flatter, thus reducing the total power of the eye. However, they are substantially different in the way they achieve such an effect. Although LASIK removes stromal tissue, CRT produces a redistribution of the corneal thickness, affecting particularly the epithelium. In both cases, the peripheral cornea remains unchanged.

After myopia treatment with either of the aforementioned techniques, there is an increase in corneal asphericity ( *Q* ), changing from its initially prolate shape ( *Q* < 0) to an oblate contour ( *Q* > 0), being flatter in the center than in the paracentral zone surrounding the treatment area. However, even when the anterior corneal surface has been defined classically by a unique *Q* value or 2 *Q* values corresponding to the orientations of the 2 principal meridians, corneal asphericity changes significantly, depending on the peripheral reference point taken for the calculations. It also is expected that these multiaspheric concepts will be more complex after corneal refractive procedures, and even depending on the technique used. For example, wavefront-guided or topography-guided laser surgery, also know as customized LASIK is supposed to induce a less negative impact on quality of vision compared with standard LASIK procedures.

Alterations in *Q* produce an increase in optical aberrations with a significant impact in the quality of vision, but also on contrast sensitivity and other aspects of visual function, such as night vision disturbances. With the development of techniques for measuring optical quality of the eye, several studies have allowed for better knowledge of the optical quality of the corneal surface after LASIK or CRT. Both refractive techniques significantly increase higher-order aberrations (HOAs) in the eye, particularly third- and fourth-order aberrations. These particular aberrations have been shown to be those with more impact in the visual quality of the eye.

The ocular aberrations are major determinant factors of the retinal image quality. These aberrations of the eye are the combination of aberrations of the anterior corneal surface plus those from the internal ocular media and depend on many factors and conditions: changing from person to person and depending on the pupil size, age, accommodation, retinal eccentricity, and the refractive condition.

Because the treatment zones vary significantly according to treatment technique and the cornea’s response to the different correction procedures, and because the cornea possesses different degrees of asphericity according to the corneal zone being analyzed, it is important to study aberration values for different corneal diameters to characterize fully this important property that defines the postsurgical corneal contour, as well as to evaluate its impact on the HOAs induced as a consequence of such changes. The purpose of this study was to evaluate the changes of different HOAs of the corneal anterior surface as a function of diameter being analyzed after 2 surgical and 1 nonsurgical refractive treatments (CRT, standard LASIK, and custom LASIK).

## Methods

## Subjects and Inclusion Criterion

The clinical records of 81 patients who underwent CRT (n = 27), standard LASIK (n = 27), and customized LASIK (n = 27) at the ophthalmology clinic Novovision, Madrid, Spain, were analyzed retrospectively and their corneal topography results were processed using custom Vol-CT software version 6.99 (Sarver & Associates, Inc, Carbondale, Illinois, USA). Only the right eye from each patient was considered for statistical analysis to avoid the known correlation between the response to treatment of both eyes from same individual. Only patients with myopia between −0.75 and −4.25 diopters (D) and astigmatism of less than −1.75 D were included to match the range of treatments more commonly performed in CRT. When the right eye did not meet the previous inclusion criterion, the left eye was used. No patient had ocular disease or had undergone previous ocular surgery. Complete optometric and ophthalmologic examinations were performed before surgical and nonsurgical correction of myopia through the aforementioned techniques. A minimum of 3 months was required to guarantee that the topography was stable. After that, the patients had to demonstrate successful treatment as evidenced by residual refractive error (≤ ± 0.50), visual acuity (≥ 20/20 or higher uncorrected visual acuity), surface regularity and centering of the treatment zone (less than 0.5 mm of decentration) before being elected for this study. Another important inclusion criterion was that the videokeratoscope examinations had to have been performed between 4:00 pm and 8:00 pm to minimize the influence of diurnal variations in corneal thickness that potentially may influence anterior corneal topography.

## Laser In Situ Keratomileusis Surgery

In all cases, the ablation was central, with an optic zone of 6.50 mm for all LASIK treatments. A transition zone of 0.30 mm for the spherical cases in the standard LASIK group and 1.25 mm for astigmatic corrections and custom LASIK procedures was used. The surgical routine for LASIK followed international standards, and the commonly accepted criteria for refractive surgery procedures were observed regarding predictability, efficacy, and safety. After creating a-120 μm, 9.5-mm diameter flap with a Hansatome microkeratome (Chiron Vision, model 2765; Bausch & Lomb, Claremont, California, USA), standard LASIK and custom LASIK ablation profiles were produced using the Allegretto Wave Eye-Q 400-Hz laser (Wavelight, Erlangen, Germany). All surgical procedures were uneventful and successful.

## Corneal Refractive Therapy Lens Characteristics

The rigid gas permeable material used for the CRT lenses (paflufocon D; Dk = 100 barrer; Paragon Vision Sciences, Mesa, Arizona, USA) with parameters, base curve radius (8.52 ± 0.22 mm; range, 8.2 to 9.0 mm), return zone depth (531.00 ± 23.14 μm range, 500 to 575 μm), and landing zone angle (32.72 ± 1.10 degrees; range, 31 to 35 degrees). Trial lenses were derived from nomograms in the form of sliding tables produced by the manufacturer of Paragon CRT sigmoid reverse geometry contact lens (Paragon Vision Sciences, Mesa, Arizona, USA). Fitting was evaluated according to the recommendations of the manufacturer regarding fluorescein pattern, topographical evaluation, and refractive and visual outcomes.

## Computing Corneal Monochromatic Higher-Order Aberrations from Corneal Topography

Topographic data were obtained using the Atlas Mastervue videokeratoscope (Humphrey Zeiss Instruments, San Leandro, California, USA). The corneal topographer was calibrated before data acquisition according to the manufacturer’s recommendations. Corneal videokeratographic data were downloaded onto floppy disks in ASCII file format, which contained information about corneal elevation, curvature, power, and position of the pupil.

HOAs were expressed as Zernike polynomials Z _{3− }^{3 }to Z _{6 }^{6 }, which comprise corneal aberrations up to the sixth order using the calculations facility of Vol-CT 6.89 software. Total HOA root mean square (RMS) and RMS values for the third, fourth, fifth, and sixth order were calculated. Total HOA RMS (including Zernike polynomials Z _{3− }, ^{3 }Z _{3− }, ^{1 }… , Z _{6 }, ^{4 }Z _{6 }^{6 }), spherical-like aberrations (including Zernike polynomials Z _{4 }^{0 }and Z _{6 }^{0 }), coma-like aberrations (including Zernike polynomials Z _{3− }, ^{1 }Z _{3 }, ^{1 }Z _{5− }, ^{1 }and Z _{5 }^{1 }), secondary astigmatism (including Zernike polynomials Z _{4− }, ^{2 }Z _{4 }, ^{2 }Z _{6− }, ^{2 }and Z _{6 }^{2 }), and another RMS resulting from the sum of spherical-like and coma-like aberrations. All aberrations were calculated for an aperture diameter of between 3 and 8 mm (Sph_3 mm to Sph_8 mm for spherical-like aberrations, Coma_3 mm to Coma_8 mm for coma-like aberrations, Total_3 mm to Total_8 mm for total aberrations, and Astig_3 mm to Astig_8 mm for secondary astigmatism).

## Statistical Analysis

The SPSS software package version 16 (SPSS, Inc, Chicago, Illinois, USA) was used for statistical analysis. The Kolmogorov-Smirnov test was applied to assess the normality of data distribution. The Kruskal-Wallis test or analysis of variance (ANOVA) were performed to evaluate whether statistically different values were present among the clinical groups of standard LASIK, custom LASIK, and CRT. When normality could not be assumed, the Wilcoxon signed-ranks test was used for paired comparison between techniques and the paired samples test was used when normality could be assumed for pair comparisons between treatments. For statistical purposes, a *P *value less than .05 was considered statistically significant.

## Results

The mean age was 29.94 ± 7.5 years (range, 16 to 49 years) for the 81 subjects, of which 50 were female (61.7%) and 31 were male (38.3%). Total preoperative spherical equivalent was −2.82 ± 0.77 D and ranged from −1.50 to −4.38 D.

Table 1 presents descriptive data for demographic characteristics and the refractive components M, J _{0 }, and J45 before treatment and for statistical comparison between the 3 treatment groups. No statistically significant differences were found for the comparison of spherical equivalent ( *P *= .998, Kruskal-Wallis test), nor for J _{0 }or J45 between the 3 conditions before treatment.

Standard LASIK (n = 27) | Custom LASIK (n = 27) | Corneal Refractive Therapy (n = 27) | P Value | |
---|---|---|---|---|

Gender (female/male) | 21/6 | 12/15 | 17/10 | .037 ^{a } |

Age (yrs) | 32.30 ± 5.79 | 31.07 ± 5.33 | 26.44 ± 9.67 | .009 ^{b } |

23/48 | 25/43 | 16/49 | ||

Interval (mos) | 5.04 ± 2.31 | 5.28 ± 1.83 | 3.79 ± 1.42 | .005 ^{a } |

3.00/9.63 | 3.00/8.23 | 3.00/8.93 | ||

Sphere (D) | −2.42 ± 0.75 | −2.62 ± 0.78 | −2.54 ± 0.75 | .716 ^{a } |

−3.75/−0.75 | −4.25/−1.50 | −4.25/−1.50 | ||

Cylinder (D) | −0.80 ± 0.58 | −0.41 ± 0.44 | −0.56 ± 0.45 | .028 ^{a } |

−1.75/0.00 | −1.50/0.00 | −1.75/0.00 | ||

M (D) | −2.82 ± 0.77 | −2.82 ± 0.79 | −2.82 ± 0.78 | .998 ^{a } |

−4.25/−1.63 | −4.38/−1.50 | −4.38/−1.63 | ||

J _{0 }(D) |
0.23 ± 0.41 | 0.11 ± 0.22 | 0.15 ± 0.29 | .406 ^{a } |

−0.65/0.88 | −0.25/0.74 | −0.47/0.86 | ||

J _{45 }(D) |
−0.01 ± 0.17 | −0.03 ± 0.17 | −0.03 ± 0.16 | .971 ^{a } |

−0.48/0.38 | −0.63/0.43 | −0.40/0.37 |

Preoperative data for the different RMS values analyzed are presented in Tables 2, 3, and 4 . There were no statistically significant differences between the 3 techniques for all RMS values at all diameters under analysis, with the exception of Coma_4 mm ( *P *= .038, ANOVA), Sph_6 mm ( *P *= .032, ANOVA), and Sph_7 mm (i = .041, ANOVA).

RMS | 3 mm | 4 mm | 5 mm | 6 mm | 7 mm | 8 mm |
---|---|---|---|---|---|---|

Third order | ||||||

Before | 0.038 ± 0.016 | 0.070 ± 0.031 | 0.150 ± 0.081 | 0.297 ± 0.180 | 0.544 ± 0.307 | 0.964 ± 0.515 |

After | 0.050 ± 0.021 | 0.084 ± 0.033 | 0.185 ± 0.106 | 0.400 ± 0.254 | 0.795 ± 0.439 | 1.408 ± 0.682 |

Difference | 0.012 ± 0.020 | 0.014 ± 0.042 | 0.035 ± 0.120 | 0.103 ± 0.305 | 0.250 ± 0.518 | 0.444 ± 0.827 |

P value |
.005 ^{a } |
.106 ^{b } |
.091 ^{a } |
.066 ^{a } |
.023 ^{a } |
.014 ^{a } |

Fourth order | ||||||

Before | 0.027 ± 0.010 | 0.063 ± 0.017 | 0.144 ± 0.043 | 0.276 ± 0.093 | 0.452 ± 0.160 | 0.686 ± 0.245 |

After | 0.036 ± 0.011 | 0.079 ± 0.023 | 0.188 ± 0.055 | 0.380 ± 0.089 | 0.701 ± 0.148 | 1.265 ± 0.275 |

Difference | 0.009 ± 0.016 | 0.016 ± 0.028 | 0.045 ± 0.074 | 0.104 ± 0.135 | 0.250 ± 0.220 | 0.580 ± 0.361 |

P value |
.010 ^{b } |
.006 ^{b } |
.004 ^{a } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{b } |

Fifth order | ||||||

Before | 0.025 ± 0.009 | 0.038 ± 0.016 | 0.061 ± 0.032 | 0.106 ± 0.076 | 0.183 ± 0.128 | 0.286 ± 0.188 |

After | 0.026 ± 0.012 | 0.047 ± 0.017 | 0.093 ± 0.053 | 0.152 ± 0.102 | 0.256 ± 0.169 | 0.421 ± 0.246 |

Difference | 0.001 ± 0.015 | 0.008 ± 0.018 | 0.032 ± 0.063 | 0.046 ± 0.131 | 0.074 ± 0.218 | 0.134 ± 0.305 |

P value |
.733 ^{b } |
.030 ^{a } |
.009 ^{a } |
.023 ^{a } |
.011 ^{a } |
.003 ^{a } |

Sixth order | ||||||

Before | 0.021 ± 0.011 | 0.032 ± 0.014 | 0.050 ± 0.036 | 0.078 ± 0.062 | 0.126 ± 0.090 | 0.200 ± 0.134 |

After | 0.024 ± 0.012 | 0.044 ± 0.022 | 0.070 ± 0.040 | 0.098 ± 0.056 | 0.168 ± 0.090 | 0.258 ± 0.126 |

Difference | 0.002 ± 0.018 | 0.012 ± 0.029 | 0.020 ± 0.060 | 0.020 ± 0.080 | 0.042 ± 0.132 | 0.058 ± 0.183 |

P value |
.517 ^{a } |
.055 ^{a } |
.078 ^{a } |
.073 ^{a } |
.066 ^{a } |
.046 ^{a } |

Total | ||||||

Before | 0.060 ± 0.017 | 0.111 ± 0.025 | 0.231 ± 0.080 | 0.446 ± 0.182 | 0.773 ± 0.307 | 1.290 ± 0.481 |

After | 0.074 ± 0.023 | 0.137 ± 0.030 | 0.302 ± 0.100 | 0.609 ± 0.226 | 1.152 ± 0.368 | 2.034 ± 0.544 |

Difference | 0.014 ± 0.025 | 0.026 ± 0.036 | 0.071 ± 0.126 | 0.163 ± 0.302 | 0.380 ± 0.496 | 0.744 ± 0.731 |

P value |
.007 ^{a } |
.001 ^{b } |
.006 ^{a } |
.005 ^{a } |
.001 ^{a } |
< .001 ^{a } |

Sph | ||||||

Before | 0.017 ± 0.008 | 0.049 ± 0.015 | 0.105 ± 0.040 | 0.208 ± 0.087 | 0.348 ± 0.142 | 0.531 ± 0.238 |

After | 0.018 ± 0.009 | 0.056 ± 0.024 | 0.137 ± 0.044 | 0.298 ± 0.090 | 0.593 ± 0.161 | 1.114 ± 0.291 |

Difference | 0.001 ± 0.012 | 0.007 ± 0.022 | 0.032 ± 0.051 | 0.090 ± 0.121 | 0.245 ± 0.197 | 0.583 ± 0.318 |

P value |
.812 ^{b } |
.136 ^{b } |
.004 ^{b } |
.001 ^{b } |
< .001 ^{b } |
< .001 ^{b } |

Coma | ||||||

Before | 0.019 ± 0.008 | 0.044 ± 0.025 | 0.108 ± 0.084 | 0.230 ± 0.164 | 0.444 ± 0.285 | 0.803 ± 0.456 |

After | 0.029 ± 0.014 | 0.063 ± 0.031 | 0.155 ± 0.099 | 0.340 ± 0.220 | 0.675 ± 0.395 | 1.228 ± 0.661 |

Difference | 0.010 ± 0.017 | 0.019 ± 0.038 | 0.047 ± 0.116 | 0.110 ± 0.247 | 0.232 ± 0.403 | 0.425 ± 0.663 |

P value |
.008 ^{a } |
.003 ^{a } |
.016 ^{a } |
.015 ^{a } |
.008 ^{a } |
.003 ^{a } |

Astig | ||||||

Before | 0.010 ± 0.005 | 0.017 ± 0.008 | 0.043 ± 0.040 | 0.092 ± 0.074 | 0.172 ± 0.124 | 0.288 ± 0.181 |

After | 0.019 ± 0.010 | 0.033 ± 0.016 | 0.071 ± 0.049 | 0.125 ± 0.091 | 0.214 ± 0.132 | 0.393 ± 0.221 |

Difference | 0.009 ± 0.010 | 0.016 ± 0.017 | 0.028 ± 0.062 | 0.033 ± 0.119 | 0.042 ± 0.188 | 0.105 ± 0.263 |

P value |
< .001 ^{a } |
< .001 ^{b } |
.036 ^{a } |
.174 ^{a } |
.316 ^{a } |
.038 ^{a } |

Sph + coma | ||||||

Before | 0.027 ± 0.007 | 0.069 ± 0.019 | 0.165 ± 0.064 | 0.338 ± 0.124 | 0.605 ± 0.227 | 1.020 ± 0.382 |

After | 0.036 ± 0.012 | 0.089 ± 0.026 | 0.222 ± 0.071 | 0.485 ± 0.156 | 0.952 ± 0.282 | 1.738 ± 0.488 |

Difference | 0.009 ± 0.014 | 0.019 ± 0.030 | 0.058 ± 0.085 | 0.147 ± 0.178 | 0.347 ± 0.278 | 0.718 ± 0.446 |

P value |
.003 ^{b } |
.001 ^{a } |
.001 ^{a } |
.001 ^{a } |
< .001 ^{b } |
< .001 ^{a } |

RMS | 3 mm | 4 mm | 5 mm | 6 mm | 7 mm | 8 mm |
---|---|---|---|---|---|---|

Third order | ||||||

Before | 0.038 ± 0.014 | 0.080 ± 0.029 | 0.161 ± 0.075 | 0.299 ± 0.122 | 0.589 ± 0.249 | 1.057 ± 0.487 |

After | 0.051 ± 0.028 | 0.102 ± 0.060 | 0.199 ± 0.106 | 0.372 ± 0.190 | 0.657 ± 0.340 | 1.194 ± 0.611 |

Difference | 0.013 ± 0.028 | 0.022 ± 0.061 | 0.037 ± 0.126 | 0.073 ± 0.237 | 0.068 ± 0.426 | 0.138 ± 0.736 |

P value |
.024 ^{a } |
.124 ^{a } |
.163 ^{a } |
.212 ^{a } |
.581 ^{a } |
.340 ^{b } |

Fourth order | ||||||

Before | 0.026 ± 0.009 | 0.060 ± 0.015 | 0.130 ± 0.060 | 0.255 ± 0.071 | 0.435 ± 0.125 | 0.721 ± 0.243 |

After | 0.038 ± 0.015 | 0.073 ± 0.028 | 0.165 ± 0.077 | 0.328 ± 0.134 | 0.684 ± 0.190 | 1.260 ± 0.322 |

Difference | 0.012 ± 0.018 | 0.013 ± 0.030 | 0.035 ± 0.096 | 0.073 ± 0.155 | 0.249 ± 0.226 | 0.540 ± 0.421 |

P value |
.002 ^{a } |
.032 ^{b } |
.005 ^{a } |
.014 ^{a } |
< .001 ^{a } |
< .001 ^{a } |

Fifth order | ||||||

Before | 0.024 ± 0.008 | 0.037 ± 0.014 | 0.068 ± 0.041 | 0.135 ± 0.081 | 0.227 ± 0.122 | 0.351 ± 0.175 |

After | 0.027 ± 0.011 | 0.049 ± 0.022 | 0.080 ± 0.050 | 0.138 ± 0.091 | 0.242 ± 0.121 | 0.412 ± 0.179 |

Difference | 0.003 ± 0.012 | 0.012 ± 0.026 | 0.011 ± 0.067 | 0.003 ± 0.139 | 0.015 ± 0.193 | 0.062 ± 0.247 |

P value |
.180 ^{b } |
.037 ^{a } |
.239 ^{a } |
.923 ^{a } |
.597 ^{a } |
.163 ^{a } |

Sixth order | ||||||

Before | 0.018 ± 0.008 | 0.029 ± 0.011 | 0.051 ± 0.033 | 0.091 ± 0.064 | 0.143 ± 0.092 | 0.210 ± 0.107 |

After | 0.023 ± 0.007 | 0.042 ± 0.025 | 0.060 ± 0.041 | 0.102 ± 0.073 | 0.187 ± 0.124 | 0.270 ± 0.133 |

Difference | 0.005 ± 0.010 | 0.012 ± 0.028 | 0.009 ± 0.056 | 0.011 ± 0.108 | 0.044 ± 0.178 | 0.060 ± 0.185 |

P value |
.013 ^{a } |
.046 ^{a } |
.442 ^{a } |
.866 ^{a } |
.230 ^{a } |
.149 ^{a } |

Total | ||||||

Before | 0.057 ± 0.013 | 0.114 ± 0.022 | 0.230 ± 0.098 | 0.438 ± 0.140 | 0.801 ± 0.257 | 1.372 ± 0.506 |

After | 0.076 ± 0.027 | 0.147 ± 0.060 | 0.283 ± 0.132 | 0.539 ± 0.229 | 1.024 ± 0.353 | 1.865 ± 0.545 |

Difference | 0.019 ± 0.027 | 0.033 ± 0.061 | 0.053 ± 0.165 | 0.101 ± 0.296 | 0.223 ± 0.484 | 0.493 ± 0.794 |

P value |
.001 ^{a } |
.011 ^{a } |
.068 ^{a } |
.124 ^{a } |
.046 ^{a } |
.003 ^{b } |

Sph | ||||||

Before | 0.015 ± 0.007 | 0.046 ± 0.013 | 0.090 ± 0.041 | 0.160 ± 0.073 | 0.264 ± 0.148 | 0.425 ± 0.236 |

After | 0.018 ± 0.011 | 0.046 ± 0.024 | 0.116 ± 0.058 | 0.267 ± 0.093 | 0.609 ± 0.201 | 1.142 ± 0.362 |

Difference | 0.003 ± 0.013 | 0.000 ± 0.029 | 0.027 ± 0.063 | 0.108 ± 0.113 | 0.344 ± 0.185 | 0.717 ± 0.332 |

P value |
.194 ^{b } |
.885 ^{a } |
.038 ^{b } |
< .001 ^{b } |
< .001 ^{b } |
< .001 ^{b } |

Coma | ||||||

Before | 0.026 ± 0.012 | 0.063 ± 0.026 | 0.129 ± 0.067 | 0.258 ± 0.111 | 0.509 ± 0.258 | 0.866 ± 0.480 |

After | 0.035 ± 0.016 | 0.078 ± 0.046 | 0.158 ± 0.080 | 0.295 ± 0.141 | 0.554 ± 0.283 | 1.080 ± 0.563 |

Difference | 0.009 ± 0.015 | 0.015 ± 0.048 | 0.028 ± 0.106 | 0.037 ± 0.181 | 0.045 ± 0.369 | 0.214 ± 0.662 |

P value |
.006 ^{a } |
.178 ^{a } |
.079 ^{a } |
.280 ^{a } |
.532 ^{a } |
.106 ^{b } |

Astig | ||||||

Before | 0.012 ± 0.006 | 0.022 ± 0.010 | 0.050 ± 0.045 | 0.112 ± 0.093 | 0.208 ± 0.157 | 0.372 ± 0.245 |

After | 0.018 ± 0.008 | 0.034 ± 0.024 | 0.061 ± 0.050 | 0.099 ± 0.069 | 0.201 ± 0.098 | 0.377 ± 0.180 |

Difference | 0.006 ± 0.009 | 0.011 ± 0.026 | 0.011 ± 0.074 | −0.012 ± 0.124 | −0.006 ± 0.188 | 0.005 ± 0.302 |

P value |
.001 ^{a } |
.032 ^{a } |
.280 ^{a } |
.581 ^{a } |
.866 ^{a } |
.938 ^{b } |

Sph + coma | ||||||

Before | 0.031 ± 0.012 | 0.081 ± 0.020 | 0.163 ± 0.067 | 0.318 ± 0.093 | 0.609 ± 0.210 | 1.028 ± 0.395 |

After | 0.041 ± 0.015 | 0.095 ± 0.042 | 0.204 ± 0.079 | 0.414 ± 0.123 | 0.856 ± 0.252 | 1.639 ± 0.472 |

Difference | 0.010 ± 0.017 | 0.015 ± 0.045 | 0.042 ± 0.098 | 0.097 ± 0.140 | 0.246 ± 0.320 | 0.612 ± 0.602 |

P value |
.008 ^{a } |
.130 ^{a } |
.015 ^{a } |
.002 ^{a } |
.001 ^{a } |
< .001 ^{a } |

RMS | 3 mm | 4 mm | 5 mm | 6 mm | 7 mm | 8 mm |
---|---|---|---|---|---|---|

Third order | ||||||

Before | 0.039 ± 0.017 | 0.076 ± 0.028 | 0.163 ± 0.100 | 0.322 ± 0.203 | 0.646 ± 0.452 | 1.051 ± 0.611 |

After | 0.053 ± 0.019 | 0.100 ± 0.047 | 0.249 ± 0.144 | 0.540 ± 0.321 | 0.966 ± 0.595 | 1.611 ± 0.881 |

Difference | 0.014 ± 0.029 | 0.024 ± 0.051 | 0.086 ± 0.153 | 0.217 ± 0.337 | 0.321 ± 0.741 | 0.560 ± 1.028 |

P value |
.005 ^{a } |
.031 ^{a } |
.005 ^{a } |
.002 ^{a } |
.009 ^{a } |
.009 ^{b } |

Fourth order | ||||||

Before | 0.029 ± 0.014 | 0.070 ± 0.030 | 0.143 ± 0.081 | 0.291 ± 0.156 | 0.569 ± 0.390 | 0.861 ± 0.471 |

After | 0.043 ± 0.014 | 0.117 ± 0.038 | 0.297 ± 0.096 | 0.658 ± 0.143 | 1.133 ± 0.265 | 1.603 ± 0.364 |

Difference | 0.014 ± 0.020 | 0.047 ± 0.047 | 0.155 ± 0.109 | 0.368 ± 0.189 | 0.564 ± 0.456 | 0.742 ± 0.532 |

P value |
.001 ^{a } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{a } |

Fifth order | ||||||

Before | 0.025 ± 0.009 | 0.037 ± 0.022 | 0.062 ± 0.054 | 0.128 ± 0.124 | 0.260 ± 0.340 | 0.395 ± 0.415 |

After | 0.023 ± 0.008 | 0.040 ± 0.011 | 0.088 ± 0.048 | 0.180 ± 0.091 | 0.337 ± 0.137 | 0.591 ± 0.320 |

Difference | −0.002 ± 0.012 | 0.003 ± 0.024 | 0.026 ± 0.072 | 0.052 ± 0.141 | 0.077 ± 0.358 | 0.197 ± 0.487 |

P value |
.343 ^{b } |
.280 ^{a } |
.029 ^{a } |
.007 ^{a } |
.005 ^{a } |
.002 ^{a } |

Sixth order | ||||||

Before | 0.019 ± 0.010 | 0.032 ± 0.019 | 0.045 ± 0.030 | 0.086 ± 0.073 | 0.173 ± 0.206 | 0.257 ± 0.252 |

After | 0.024 ± 0.008 | 0.038 ± 0.012 | 0.075 ± 0.040 | 0.131 ± 0.070 | 0.239 ± 0.141 | 0.415 ± 0.187 |

Difference | 0.004 ± 0.014 | 0.006 ± 0.021 | 0.030 ± 0.048 | 0.045 ± 0.076 | 0.065 ± 0.224 | 0.158 ± 0.289 |

P value |
.130 ^{a } |
.052 ^{a } |
.002 ^{a } |
.003 ^{a } |
.002 ^{a } |
.001 ^{a } |

Total | ||||||

Before | 0.060 ± 0.020 | 0.118 ± 0.041 | 0.237 ± 0.131 | 0.478 ± 0.263 | 0.950 ± 0.669 | 1.501 ± 0.799 |

After | 0.078 ± 0.019 | 0.168 ± 0.051 | 0.420 ± 0.143 | 0.917 ± 0.258 | 1.618 ± 0.475 | 2.474 ± 0.772 |

Difference | 0.018 ± 0.031 | 0.049 ± 0.057 | 0.184 ± 0.153 | 0.439 ± 0.330 | 0.667 ± 0.805 | 0.973 ± 1.055 |

P value |
.002 ^{a } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{a } |

Sph | ||||||

Before | 0.017 ± 0.008 | 0.057 ± 0.023 | 0.116 ± 0.045 | 0.216 ± 0.089 | 0.364 ± 0.164 | 0.552 ± 0.307 |

After | 0.033 ± 0.016 | 0.105 ± 0.043 | 0.261 ± 0.108 | 0.585 ± 0.178 | 1.024 ± 0.266 | 1.402 ± 0.408 |

Difference | 0.016 ± 0.016 | 0.048 ± 0.045 | 0.145 ± 0.109 | 0.369 ± 0.166 | 0.660 ± 0.228 | 0.850 ± 0.352 |

P value |
< .001 ^{b } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{b } |
< .001 ^{b } |
< .001 ^{b } |

Coma | ||||||

Before | 0.026 ± 0.014 | 0.059 ± 0.031 | 0.125 ± 0.083 | 0.260 ± 0.155 | 0.526 ± 0.315 | 0.862 ± 0.490 |

After | 0.039 ± 0.017 | 0.086 ± 0.048 | 0.222 ± 0.147 | 0.496 ± 0.318 | 0.901 ± 0.583 | 1.448 ± 0.840 |

Difference | 0.013 ± 0.020 | 0.027 ± 0.049 | 0.098 ± 0.147 | 0.236 ± 0.308 | 0.375 ± 0.644 | 0.586 ± 0.928 |

P value |
.003 ^{a } |
.014 ^{a } |
.001 ^{a } |
.001 ^{a } |
.009 ^{a } |
.003 ^{b } |

Astig | ||||||

Before | 0.010 ± 0.005 | 0.022 ± 0.023 | 0.042 ± 0.047 | 0.096 ± 0.075 | 0.217 ± 0.220 | 0.325 ± 0.236 |

After | 0.017 ± 0.008 | 0.035 ± 0.018 | 0.087 ± 0.075 | 0.176 ± 0.143 | 0.342 ± 0.200 | 0.541 ± 0.274 |

Difference | 0.007 ± 0.011 | 0.012 ± 0.022 | 0.045 ± 0.080 | 0.080 ± 0.166 | 0.125 ± 0.294 | 0.217 ± 0.353 |

P value |
.002 ^{b } |
.002 ^{a } |
.002 ^{a } |
.020 ^{a } |
.005 ^{a } |
.002 ^{a } |

Sph + coma | ||||||

Before | 0.033 ± 0.013 | 0.085 ± 0.032 | 0.178 ± 0.078 | 0.356 ± 0.136 | 0.684 ± 0.254 | 1.111 ± 0.376 |

After | 0.053 ± 0.017 | 0.141 ± 0.051 | 0.363 ± 0.136 | 0.817 ± 0.226 | 1.446 ± 0.413 | 2.115 ± 0.665 |

Difference | 0.020 ± 0.020 | 0.057 ± 0.052 | 0.185 ± 0.129 | 0.460 ± 0.235 | 0.762 ± 0.450 | 1.005 ± 0.700 |

P value |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{a } |
< .001 ^{b } |
< .001 ^{b } |

Tables 2, 3, and 4 show the values of different aberrations analyzed for the standard LASIK, custom LASIK, and CRT groups before treatment and after treatment and the differences between them (mean ± standard deviation). Statistical significance is shown for the difference in all values of the aberrations studied and for the different diameters from 3 to 8 mm. We found statistically significant differences in all diameters for the fourth-order RMS, total RMS, coma-like RMS, and spherical plus coma RMS in the standard LASIK group. In the custom LASIK, group we found statistically significant differences only in the fourth-order aberrations in all diameters. Moreover, the custom LASIK treatment was the one with fewer items (RMS for a certain diameter) showing statistically significant changes. In the case of CRT, all aberrations showed statistically significant differences, except for the fifth-order and sixth-order RMS.

Table 5 shows the values of change in RMS for the standard LASIK, custom LASIK, and CRT interventions (mean posttreatment minus baseline ± standard deviation), the statistical comparison between laser treatments (standard LASIK vs custom LASIK), and among all treatments (standard LASIK, custom LASIK, and CRT). No statistically significant differences were found for the comparison of standard LASIK and custom LASIK ( *P *> .063, *t *test). Statistical analysis showed that spherical-like RMS was significantly different among treatments for all diameters. When the analysis was performed for the 3 treatments, there were statistically significant differences for all diameters studied from 3 to 8 mm only in the spherical-like RMS.

RMS | 3 mm | 4 mm | 5 mm | 6 mm | 7 mm | 8 mm |
---|---|---|---|---|---|---|

Third order | ||||||

SL | 0.012 ± 0.020 | 0.014 ± 0.042 | 0.035 ± 0.120 | 0.103 ± 0.305 | 0.250 ± 0.518 | 0.444 ± 0.827 |

CL | 0.013 ± 0.028 | 0.022 ± 0.061 | 0.037 ± 0.126 | 0.073 ± 0.237 | 0.068 ± 0.426 | 0.138 ± 0.736 |

CRT | 0.014 ± 0.029 | 0.024 ± 0.051 | 0.086 ± 0.153 | 0.217 ± 0.337 | 0.321 ± 0.741 | 0.560 ± 1.028 |

P value ^{a }/ P value ^{b } |
.943 ^{c }/.761 ^{d } |
.573 ^{e }/.754 ^{f } |
.953 ^{e }/0.301 ^{f } |
.692 ^{e }/.174 ^{f } |
.168 ^{e }/.261 ^{f } |
.160 ^{e }/.192 ^{f } |

Fourth order | ||||||

SL | 0.009 ± 0.016 | 0.016 ± 0.028 | 0.045 ± 0.074 | 0.104 ± 0.135 | 0.250 ± 0.220 | 0.580 ± 0.361 |

CL | 0.012 ± 0.018 | 0.013 ± 0.030 | 0.035 ± 0.096 | 0.073 ± 0.155 | 0.249 ± 0.226 | 0.540 ± 0.421 |

CRT | 0.014 ± 0.020 | 0.047 ± 0.047 | 0.155 ± 0.109 | 0.368 ± 0.189 | 0.564 ± 0.456 | 0.742 ± 0.532 |

P value ^{a }/ P value ^{b } |
.594 ^{c }/.520 ^{f } |
.670 ^{e }/ .001 ^{f } |
.346 ^{c }/ < .001 ^{d } |
.286 ^{c }/ < .001 ^{d } |
.991 ^{e }/ < .001 ^{d } |
.712 ^{e }/.215 ^{f } |

Fifth order | ||||||

SL | 0.001 ± 0.015 | 0.008 ± 0.018 | 0.032 ± 0.063 | 0.046 ± 0.131 | 0.074 ± 0.218 | 0.134 ± 0.305 |

CL | 0.003 ± 0.012 | 0.012 ± 0.026 | 0.011 ± 0.067 | 0.003 ± 0.139 | 0.015 ± 0.193 | 0.062 ± 0.247 |

CRT | −0.002 ± 0.012 | 0.003 ± 0.024 | 0.026 ± 0.072 | 0.052 ± 0.141 | 0.077 ± 0.358 | 0.197 ± 0.487 |

P value ^{a }/ P value ^{b } |
.578 ^{e }/.325 ^{f } |
.547 ^{e }/.297 ^{f } |
.488 ^{c }/.673 ^{d } |
.374 ^{c }/.178 ^{d } |
.294 ^{c }/.053 ^{d } |
.403 ^{c }/.060 ^{d } |

Sixth order | ||||||

SL | 0.002 ± 0.018 | 0.012 ± 0.029 | 0.020 ± 0.060 | 0.020 ± 0.080 | 0.042 ± 0.132 | 0.058 ± 0.183 |

CL | 0.005 ± 0.010 | 0.012 ± 0.028 | 0.009 ± 0.056 | 0.011 ± 0.108 | 0.044 ± 0.178 | 0.060 ± 0.185 |

CRT | 0.004 ± 0.014 | 0.006 ± 0.021 | 0.030 ± 0.048 | 0.045 ± 0.076 | 0.065 ± 0.224 | 0.158 ± 0.289 |

P value ^{a }/ P value ^{b } |
.497 ^{e }/.782 ^{f } |
.845 ^{c }/.940 ^{d } |
.455 ^{c }/.207 ^{d } |
.355 ^{c }/.061 ^{d } |
.950 ^{e }/.354 ^{d } |
.968 ^{e }/.186 ^{f } |

Total | ||||||

SL | 0.014 ± 0.025 | 0.026 ± 0.036 | 0.071 ± 0.126 | 0.163 ± 0.302 | 0.380 ± 0.496 | 0.744 ± 0.731 |

CL | 0.019 ± 0.027 | 0.033 ± 0.061 | 0.053 ± 0.165 | 0.101 ± 0.296 | 0.223 ± 0.484 | 0.493 ± 0.794 |

CRT | 0.018 ± 0.031 | 0.049 ± 0.057 | 0.184 ± 0.153 | 0.439 ± 0.330 | 0.667 ± 0.805 | 0.973 ± 1.055 |

P value ^{a }/ P value ^{b } |
.346 ^{c }/.761 ^{f } |
.986 ^{c }/.261 ^{f } |
.182 ^{c }/ .004 ^{f } |
.182 ^{c }/ < .001 ^{f } |
.251 ^{e }/ < .001 ^{d } |
.238 ^{e }/.137 ^{f } |

Sph | ||||||

SL | 0.001 ± 0.012 | 0.007 ± 0.022 | 0.032 ± 0.051 | 0.090 ± 0.121 | 0.245 ± 0.197 | 0.583 ± 0.318 |

CL | 0.003 ± 0.013 | 0.000 ± 0.029 | 0.027 ± 0.063 | 0.108 ± 0.113 | 0.344 ± 0.185 | 0.717 ± 0.332 |

CRT | 0.016 ± 0.016 | 0.048 ± 0.045 | 0.145 ± 0.109 | 0.369 ± 0.166 | 0.660 ± 0.228 | 0.850 ± 0.352 |

P value ^{a }/ P value ^{b } |
.418 ^{e }/ < .001 ^{f } |
.334 ^{e }/ < .001 ^{f } |
.730 ^{e }/ < .001 ^{d } |
.578 ^{e }/ < .001 ^{f } |
.063 ^{e }/ < .001 ^{f } |
.139 ^{e }/ .026 ^{d } |

Coma | ||||||

SL | 0.010 ± 0.017 | 0.029 ± 0.045 | 0.047 ± 0.116 | 0.110 ± 0.247 | 0.232 ± 0.403 | 0.425 ± 0.663 |

CL | 0.009 ± 0.015 | 0.015 ± 0.048 | 0.028 ± 0.106 | 0.037 ± 0.181 | 0.045 ± 0.369 | 0.214 ± 0.662 |

CRT | 0.013 ± 0.020 | 0.027 ± 0.049 | 0.098 ± 0.147 | 0.236 ± 0.308 | 0.375 ± 0.644 | 0.586 ± 0.928 |

P value ^{a }/ P value ^{b } |
.734 ^{e }/.732 ^{f } |
.278 ^{e }/.503 ^{f } |
.423 ^{c }/.228 ^{d } |
.223 ^{e }/ .016 ^{f } |
.085 ^{e }/.051 ^{f } |
.250 ^{e }/.205 ^{f } |

Astig | ||||||

SL | 0.009 ± 0.010 | 0.018 ± 0.018 | 0.028 ± 0.062 | 0.033 ± 0.119 | 0.042 ± 0.188 | 0.105 ± 0.263 |

CL | 0.006 ± 0.009 | 0.011 ± 0.026 | 0.011 ± 0.074 | −0.012 ± 0.124 | −0.006 ± 0.188 | 0.005 ± 0.302 |

CRT | 0.007 ± 0.011 | 0.012 ± 0.022 | 0.045 ± 0.080 | 0.080 ± 0.166 | 0.125 ± 0.294 | 0.217 ± 0.353 |

P value ^{a }/ P value ^{b } |
.499 ^{c }/.640 ^{f } |
.105 ^{c }/.473 ^{f } |
.365 ^{e }/.413 ^{d } |
.182 ^{e }/.122 ^{d }/.122 ^{d } |
.350 ^{e }/.096 ^{d } |
.203 ^{e }/.419 ^{d } |

Sph + coma | ||||||

SL | 0.009 ± 0.014 | 0.019 ± 0.030 | 0.058 ± 0.085 | 0.147 ± 0.178 | 0.347 ± 0.278 | 0.718 ± 0.446 |

CL | 0.010 ± 0.017 | 0.015 ± 0.045 | 0.042 ± 0.098 | 0.097 ± 0.140 | 0.246 ± 0.320 | 0.612 ± 0.602 |

CRT | 0.020 ± 0.020 | 0.057 ± 0.052 | 0.185 ± 0.129 | 0.460 ± 0.235 | 0.762 ± 0.450 | 1.005 ± 0.700 |

P value ^{a }/ P value ^{b } |
.870 ^{e }/ .031 ^{f } |
.707 ^{e }/ .008 ^{d } |
.535 ^{e }/ < .001 ^{f } |
.260 ^{e }/ < .001 ^{d } |
.226 ^{e }/ < .001 ^{f } |
.467 ^{e }/ .048 ^{f } |