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Outcomes of topography-guided versus wavefront-optimized laser in situ keratomileusis for myopia in virgin eyes
ARTICLE
Outcomes of topography-guided versus wavefront-optimized laser in situ keratomileusis for myopia in virgin eyes Arun Kumar Jain, MD, DNB, Chintan Malhotra, MS, Anand Pasari, MS, Pawan Kumar, BSc, Majid Moshirfar, MD
PURPOSE: To compare the outcomes of topography-guided and wavefront-optimized treatment in patients having laser in situ keratomileusis (LASIK) for myopia. SETTING: Advanced Eye Centre, Post Graduate Institute of Medical Education and Research, Chandigarh, India. DESIGN: Prospective contralateral-eye case study. METHODS: Patients had topography-guided LASIK in 1 eye and wavefront-optimized LASIK in the contralateral eye using the Customized Refractive Surgery Master software and Mel 80 excimer laser. Refractive (residual manifest refraction spherical equivalent [MRSE], higher-order aberrations [HOAs]), and visual (uncorrected distance visual acuity [UDVA] and photopic and mesopic contrast sensitivity) outcomes were prospectively analyzed 6 months postoperatively. RESULTS: The study comprised 35 patients. The UDVA was 0.0 logMAR or better and the postoperative residual MRSE was G0.50 diopter in 94.29% of eyes in the topography-guided group and 85.71% of eyes in the wavefront-optimized group (P Z .09). More eyes in the topography-guided group than in the wavefront-optimized group had a UDVA of 0.1 logMAR or better (P Z .04). Topography-guided LASIK was associated with less deterioration of mesopic contrast sensitivity at higher spatial frequencies (12 cycles per degree [cpd] and 18 cpd) and lower amounts of induced coma (P Z .04) and spherical aberration (P Z .04). Less stromal tissue was ablated in the topography-guided group (mean 61.57 mm G 16.23 [SD]) than in the wavefront-optimized group (mean 79.71 G 14.81 mm) (P < .001). CONCLUSION: Although topography-guided LASIK and wavefront-optimized LASIK gave excellent results, topography-guided LASIK was associated with better contrast sensitivity, lower induction of HOAs, and a smaller amount of tissue ablation. Financial Disclosure: None of the authors has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2016; 42:1302–1311 Q 2016 ASCRS and ESCRS
Because of its efficacy and safety, laser in situ keratomileusis (LASIK) is one of the most popular procedures for the correction of refractive errors. However, there has always been a subset of patients who remain dissatisfied postoperatively because of side effects such as glare, halos, starbursts and reduced contrast sensitivity.1,2 This has been attributed in part to the ablation profile of conventional LASIK, which causes significant induction of positive spherical aberration and other higher-order aberrations (HOAs).3,4 These in turn are known to be associated with a deterioration 1302
Q 2016 ASCRS and ESCRS Published by Elsevier Inc.
in the point-spread function and modulation transfer function of the eye, manifesting clinically as a deterioration in visual quality.5 Different ablation profiles have been developed over the years in an attempt to overcome these undesirable postoperative symptoms. These include wavefront-optimized, wavefront-guided, and topography-guided ablation profiles.6 The wavefrontoptimized profile is designed to limit the induction of a positive spherical aberration without specifically targeting the preexisting patterns of HOAs in the http://dx.doi.org/10.1016/j.jcrs.2016.06.035 0886-3350
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eye by delivering an increased number of laser pulses to the corneal periphery rather than the center, which helps maintain the prolate shape of cornea postoperatively.7 The topography-guided ablation algorithm, in addition to treating spherocylindric refractive errors (ie, the lower-order aberrations [LOAs]), addresses the irregularities of the corneal elevation in an effort to reshape the cornea into an ideal curve and achieve a planar wavefront postoperatively.8 Unlike the wavefront-guided profiles, the topography-guided ablation profiles do not attempt to correct the aberrations arising from the crystalline lens or other ocular structures. Although traditionally topographic treatments have been used to treat irregular corneas,9–13 studies have also documented their safety and efficacy in the treatment of primary myopia and astigmatism.14–19 All these ablation profiles have been widely used in refractive procedures; however, no treatment algorithm has shown definite clinical superiority over others with regard to visual acuity and correction of LOAs.7 The lack of direct comparisons between wavefront-optimized and topography-guided treatment using the Mel 80 excimer laser (Carl Zeiss Meditec AG) and the paucity of contralateral-eye studies prompted this prospective study to compare the efficacy and safety of the more commonly performed wavefront-optimized ablation profile with the topography-guided ablation profile for the treatment of myopia or myopic astigmatism in virgin eyes having LASIK. PATIENTS AND METHODS This prospective comparative contralateral-eye study included patients having LASIK for the correction of myopia or myopic astigmatism at the Cornea and Refractive
Submitted: December 11, 2015. Final revision submitted: May 24, 2016. Accepted: June 29, 2016. From the Advanced Eye Centre (Jain, Malhotra, Parasi, Kumar), Post Graduate Institute of Medical Education and Research, Chandigarh, India; the Department of Ophthalmology (Moshirfar), Francis I. Proctor Foundation, University of California San Francisco, San Francisco, California, USA. Presented in part at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, April 2015, and the VII World Cornea Congress, San Diego, California, USA, April 2015. Corresponding author: Arun Kumar Jain, MD, DNB, Room No 110, Advanced Eye Centre, Post Graduate Institute of Medical Education and Research, Sector 12, Chandigarh 160012, India. E-mail: [email protected].
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Services, Advanced Eye Centre, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India, between July 2013 and February 2014. Patients were enrolled after signing an informed consent form. The study was approved by the Institutional Review Board of PGIMER and adhered to the tenets of Declaration of Helsinki. For randomization, a coin toss was used to determine the treatment algorithm for the right eye of each patient; wavefront-optimized treatment was performed if the toss was a heads up, and topography-guided treatment was performed if the toss resulted in a tails up. The left eye had the opposite treatment algorithm. Inclusion criteria for the study were age 18 years to 35 years, stable refractive error with 0.50 to 6.00 diopters (D) of spherical myopia, astigmatism between 0.00 D and 3.50 D, maximum manifest spherical equivalent of 6.00 D, and distance visual acuity correctable to 0.0 logMAR or better. Exclusion criteria were presence of significant dry eye, anterior segment abnormalities (ie, cataracts, corneal scarring, or neovascularization within 1.0 mm of intended ablation zone), basement membrane disease, history of recurrent corneal erosions, progressive or unstable myopia, estimated postoperative residual stromal bed thickness of less than 250 mm, established or forme fruste keratoconus, macular or retinal disease, current use of systemic corticosteroid or immunosuppressive therapy, autoimmune disease, collagen vascular disease, diabetes mellitus, pregnancy, and lactation. The preoperative examination for each patient included uncorrected distance visual acuity (UDVA) using a standard Snellen eye chart, corrected distance visual acuity (CDVA) (with spectacles), manifest refraction, cycloplegic refraction with cyclopentolate 1.0%, postmydriatic testing at least 72 hours after cycloplegic refraction, intraocular pressure measurements, slitlamp biomicroscopy of the anterior segment, dilated fundus evaluation, Scheimpflug imaging with the Pentacam HR device (Oculus Surgical, Inc.), combined corneal topography and corneal wavefront analysis with the Atlas 9000 corneal topographer (Carl Zeiss Meditec AG), whole-eye wavefront analysis with the Wasca wavefront aberration–supported cornea ablation aberrometer (Carl Zeiss Meditec AG), and contrast sensitivity measurements (performed unioculary under photopic and mesopic conditions) with the Functional Vision Analyzer (Stereo Optical Co., Inc.). Contact lens users were asked to discontinue lens wear 2 weeks before screening for soft contact lenses and 6 weeks before screening for rigid gas-permeable contact lenses. Manifest refraction and wavefront measurements were repeated at 2 visits to ensure refractive stability. Eligible patients were scheduled for simultaneous bilateral LASIK, wavefront-optimized in 1 eye and topographyguided in the contralateral eye. The correction target was based on the manifest refraction, with emmetropia being the target in all patients. An Intralase FS 150 Hz femtosecond laser (Abbott Medical Optics, Inc.) was used for flap creation and an Mel 80 excimer laser for ablation in all eyes. The same surgeon (A.K.J.) performed all the LASIK procedures. The flap diameter varied from 8.5 to 9.5 mm, with a programmed thickness between 90 mm and 110 mm. Postoperatively, the patients were examined at 1 day, 1 week, 1 month, 3 months, and 6 months. All postoperative follow-up visits included measurement of UDVA, CDVA (if indicated), wavefront aberration–supported cornea ablation aberrometry, corneal topography using the same topographer as preoperatively, and the Functional Acuity Contrast Test (FACT).
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Device Technology
Refractive and Visual Outcomes
Customized Refractive Surgery Master software (Carl Zeiss Meditec AG) was locally networked with the Atlas topographer (which uses Placido disk technology) and the Wasca wavefront aberration–supported cornea ablation analyzer (a high-resolution Hartmann-Shack aberrometer), thus enabling integration of topographic and wavefront data. With this setup, aspheric spherocylindrical refractive ablations (wavefront-optimized ablations) are generated using manifest refraction values entered manually. Two aspheric profiles are available. One is designed to reduce the ablation depth in borderline corneas, and the other is optimized for asphericity. The corneal topography–based ablation algorithms use topographic and corneal elevation data and can be applied in the following ways: (1) as a purely topographic smoothening algorithm for conditions such as small optic zones, decentered ablations, or irregular astigmatism, where the aim is to correct the corneal irregularity without targeting the spherocylindrical error (the limit for the asymmetric ablation being 50 mm), or (2) as a topographic refractive algorithm, which simultaneously corrects the refractive error and also smoothens the cornea, thus targeting maintenance of corneal asphericity and minimal induction of HOAs. Except for the 2 treatment algorithms (ie, wavefrontoptimized or topography-guided) no nomogram correction was performed for either arm of the study, the rationale being that nomogram adjustment is required for treating highly irregular corneas, for which the topographysmooth ablation profile is used first to normalize the cornea without targeting the LOAs of sphere and cylinder. However, this ablation itself induces changes in LOAs and hence necessitates nomogram adjustment. Because virgin myopic eyes without significant corneal irregularities were included in the present study, no additional nomogram adjustment was performed.
Figure 1 shows the refractive and visual outcomes in the topography-guided group and Figure 2, in the wavefront-optimized group.
Statistical Analysis The continuous data are presented as the mean G SD or the median and interquartile range, as appropriate. The normality of quantitative data was checked by measures of Kolmogorov-Smirnov tests. The Mann-Whitney U test was used for statistical analysis of skewed continuous variables. For normally distributed data, the t test was used to compare the 2 treatment groups. For time-related and repeated measures of HOAs, 1-way analysis of variance followed by Bonferroni correction for multiple comparisons were used. The qualitative or categorical variables were described as frequencies and proportions. The proportions were compared using the chi-square or Fisher exact test, whichever was applicable. A P value less than 0.05 was considered to indicate statistical significance. All calculations were performed using SPSS software (version 20, SPSS, Inc.).
Efficacy Both procedures were equally efficacious at the end of the 6-month follow-up, with a mean efficacy index (ratio of postoperative decimal UDVA to preoperative decimal CDVA) of 1.013 G 0.12 (SD) in the wavefrontoptimized group and 1.053 G 0.11 in the topographyguided group (P Z .151). Thirty-three eyes (94.3%) in the topography-guided group and 30 eyes (85.71%) in the wavefront-optimized group had a UDVA of 0.0 logMAR (20/20) or better (P Z .09) at the end of 6 months. A significantly greater proportion of eyes in the topography-guided group (10 eyes [28.57%]) than the wavefront-optimized group (5 eyes [14.29%]) had a UDVA better than 0.1 logMAR (20/16) (P Z .04). Safety The 2 ablation profiles had similar safety profiles. The mean safety index (ratio of mean preoperative decimal CDVA to mean postoperative decimal CDVA) at 6 months was 1.054 G 0.09 in the wavefront-optimized group and 1.089 G 0.10 in the topography-guided group (P Z .128). No patient in either group had lost lines of CDVA at the end of 6 months. The CDVA was 0.0 logMAR or better in all eyes in each group. Predictability The mean manifest refraction spherical equivalent (MRSE) 6 months postoperatively was 0.17 G 0.38 D (range 1.12 to 0.62 D) and 0.02 G 0.29 D (range 0.87 to 1.00 D) in the wavefront-optimized group and topography-guided group, respectively (P Z .022). Both ablation profiles had similar predictability for MRSE within G1.0 D of emmetropia (P Z .15) and for MRSE within G0.5 D of emmetropia (P Z .09). Stability
RESULTS
Stability was similar in the 2 groups, with 4 eyes (11.42%) in the wavefront-optimized group and 2 eyes (5.71%) in the topography-guided group having an MRSE change of more than 0.5 D from 3 to 6 months postoperatively (P Z .22).
The study comprised 35 patients (70 eyes; 35 in each treatment group). Table 1 compares the preoperative and intraoperative parameters between the wavefront-optimized group and the topography-guided group.
Higher-Order Aberrations Preoperatively, ocular (whole-eye) HOAs and corneal HOAs at a 6.0 mm pupil diameter were comparable between the 2 groups (Table 2). At 6 months,
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Table 1. Between-group comparison of preoperative characteristics and intraoperative parameters. Mean G SD Parameter Sphere (D) Cylinder (D) MRSE (D) Pachymetry (mm) Flat keratometry (D) Steep keratometry (D) Optical zone (mm) Ablation depth (mm) RSB (mm)
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
3.98 G 1.24 0.29 G 0.42 3.89 G 1.85 542.20 G 23.86 43.49 G 2.41 44.02 G 1.58 6.21 G 0.15 79.71 G 14.81 361.46 G 31.46
4.19 G 1.30 0.30 G 0.38 4.19 G 1.92 540.70 G 25.38 43.39 G 1.48 43.82 G 1.52 6.28 G 0.14 61.57 G 16.23 373.69 G 34.27
.600 .596 .817 .955 .404 .482 .109 !.001* .125
MRSE Z manifest refraction spherical equivalent; RSB Z residual stromal bed; TG Z topography-guided; WFO Z wavefront-optimized *Statistically significant (P ! .05)
there was a statistically significant induction of a majority of the ocular HOAs (wavefront aberration–supported cornea ablation aberrometry), including total HOA, coma, and spherical aberration, in both groups when compared with the preoperative values (Table 3). Topography-guided ablation induced significantly lower coma (P Z .043) and spherical aberrations (P Z .04) than
wavefront-optimized ablation (Table 3). At all timepoints when HOAs were measured postoperatively, the majority of the ocular HOAs, including the total HOA root mean square (RMS), coma, and spherical aberrations, were lower in the topography-guided group than in the wavefront-optimized group, whereas trefoil was comparable between the 2 groups (Figure 3).
Figure 1. Refractive and visual outcomes in the topography-guided group (CDVA Z corrected distance visual acuity; UDVA Z uncorrected distance visual acuity; VA Z visual acuity). J CATARACT REFRACT SURG - VOL 42, SEPTEMBER 2016
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Figure 2. Refractive and visual outcomes in the wavefront-optimized group (CDVA Z corrected distance visual acuity; UDVA Z uncorrected distance visual acuity; VA Z visual acuity).
Contrast Sensitivity
within-group comparison showed no significant deterioration in contrast sensitivity under photopic conditions in either group. Testing under mesopic conditions showed significant deterioration at 12 cycles per degree (cpd) and 18 cpd in both groups compared with the preoperative levels (Figure 4).
The preoperative contrast sensitivity was similar in the wavefront-optimized group and the topographyguided group at each spatial frequency tested and under photopic conditions and mesopic conditions (Table 4). Six months after surgery, the
Table 2. Between-group comparison of preoperative ocular and corneal HOAs. Mean RMS Value (mm) G SD Preoperative Ocular HOAs (Aberrometry) Parameter Total HOAs 3rd order 4th order Coma Trefoil SA Sec astg Tetrafoil
Preoperative Corneal HOAs (Topography)
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
0.74 G 0.25 0.62 G 0.29 0.36 G 0.10 0.37 G 0.27 0.45 G 0.26 0.16 G 0.11 0.20 G 0.09 0.21 G 0.09
0.75 G 0.29 0.62 G 0.24 0.39 G 0.21 0.42 G 0.23 0.40 G 0.24 0.21 G 0.15 0.22 G 0.19 0.19 G 0.12
.904 .961 .349 .403 .427 .115 .547 .401
0.40 G 0.09 0.25 G 0.07 0.30 G 0.07 0.20 G 0.08 0.13 G 0.06 0.28 G 0.08 0.06 G 0.02 0.08 G 0.04
0.37 G 0.03 0.23 G 0.04 0.28 G 0.03 0.17 G 0.08 0.13 G 0.05 0.27 G 0.06 0.06 G 0.03 0.04 G 0.02
.223 .327 .446 .114 .148 .887 .892 .096
HOAs Z higher-order aberrations; RMS Z root mean square; SA Z spherical aberration; Sec astg Z secondary astigmatism; TG Z topography-guided; WFO Z wavefront-optimized
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Table 3. Comparison of within-group preoperative and 6-month postoperative ocular HOAs (aberrometry) and between-group comparisons of magnitude of surgically induced aberrations. Mean RMS Value (mm) G SD WFO Group Parameter Total HOAs 3rd order 4th order Coma Trefoil SA Sec astg Tetrafoil
TG Group
Magnitude of Surgically Induced HOAs
Preop (n Z 35) Postop (n Z 35) P Value Preop (n Z 35) Postop (n Z 35) P Value WFO Group 0.74 G 0.25 0.62 G 0.29 0.36 G 0.10 0.37 G 0.27 0.45 G 0.26 0.16 G 0.11 0.20 G 0.09 0.21 G 0.09
1.17 G 0.45 0.97 G 0.41 0.63 G 0.27 0.87 G 0.41 0.38 G 0.28 0.54 G 0.29 0.17 G 0.10 0.20 G 0.10
.001* .004* !.001* !.001* .121 !.001* .135 .223
0.75 G 0.29 0.62 G 0.24 0.39 G 0.21 0.42 G 0.23 0.40 G 0.24 0.21 G 0.15 0.22 G 0.19 0.19 G 0.12
1.07 G 0.38 0.88 G 0.39 0.57 G 0.24 0.71 G 0.44 0.35 G 0.33 0.48 G 0.27 0.18 G 0.11 0.15 G 0.09
.012* .029* .049* .036* .466 .001* .317 .091
0.43 0.35 0.2 0.50 0.07 0.38 0.03 0.01
TG Group 0.32 0.26 0.28 0.29 0.05 0.27 0.04 0.04
P Value .34 .46 .63 .043* .92 .04* .63 .70
HOAs Z higher order aberrations; RMS Z root mean square; SA Z spherical aberration; Sec astg Z secondary astigmatism; TG Z topography-guided; WFO Z wavefront-optimized *Statistically significant (P ! .05)
Intergroup comparison at 6 months showed that although the decrease in postoperative photopic contrast sensitivity at all tested frequencies was comparable in the 2 groups, mesopic contrast sensitivity
at the higher spatial frequencies (ie, 12 cpd and 18 cpd) had deteriorated significantly less in the topography-guided group than in the wavefrontoptimized group (Figure 5).
Figure 3. Comparison of wavefront-optimized LASIK and topography-guided LASIK with respect to induced ocular HOAs in the postoperative period (HOAs Z higher-order aberrations; RMS Z root mean square; TG Z topography guided; WFO Z wavefront optimized). J CATARACT REFRACT SURG - VOL 42, SEPTEMBER 2016
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Table 4. Intergroup comparison of preoperative photopic and mesopic contrast sensitivity on FACT (log units). Photopic Contrast Sensitivity (85 cd/m2) Frequency (Cpd) 1.5 3.0 6.0 12.0 18.0
Mesopic Contrast Sensitivity (3 cd/m2)
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
1.58 1.99 1.93 1.63 0.81
1.6 1.97 1.92 1.64 0.8
.547 .547 .731 .717 .697
1.57 1.95 1.81 1.43 0.72
1.56 1.95 1.82 1.44 0.74
.797 .732 .868 .827 .369
cd Z candelas; Cpd Z cycles per degree; TG Z topography-guided; WFO Z wavefront-optimized
DISCUSSION Expectations for the outcomes of refractive surgery are increasing progressively, with patients wanting not only spectacle independence but also excellent visual
Figure 4. Comparison of preoperative and 6-month postoperative photopic and mesopic contrast sensitivity in each group (* Z statistically significant [P ! .05]; cpd Z cycles per degree; TG Z topography guided; WFO Z wavefront optimized).
quality and increased safety. Attempts to address preexisting HOAs by wavefront-guided or topographyguided treatments are steps in this direction. Compared with wavefront measurement with aberrometers, topographic measurements from the corneal surface can measure more points, including those in the corneal periphery, which is where most of the aberrations lie. Also, corneal topography, unlike wavefront data, is unaffected by factors such as pupil size, accommodative status of the eye (which itself can induce some spherical refractive changes and HOAs), and centroid shift or by internal optical components such as early cataract. This makes the topographically acquired data a far more stable parameter than the wavefront data. In addition, topographic measurements can be used in highly aberrated eyes for which wavefront data might be unreliable. However, unlike wavefront analyzers, topographers do not provide information about the spherocylindrical refraction of the eye. Hence, topographic refractive treatment algorithms should be combined with measurements obtained from manifest refraction rather than based on
Figure 5. Comparison of wavefront-optimized LASIK and topography-guided LASIK with respect to 6-month postoperative photopic and mesopic contrast sensitivity (* Z statistically significant [P ! .05]; cpd Z cycles per degree; TG Z topography guided; WFO Z wavefront optimized).
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information acquired by the topographer alone. A potential concern with topography-guided treatments might be that treating only the corneal aberrations could unmask some lenticular HOAs (which in the virgin eye are usually balanced by HOAs arising from the cornea up to approximately age 30 years), thus leading to a less favorable ablation profile with reduced quality of vision postoperatively. In the present study, the LASIK outcomes in the topography-guided group were better than or equivalent to those in the wavefront-optimized group for the various parameters analyzed. The number of patients achieving a postoperative UDVA of 0.1 logMAR (28.57% in topography-guided group versus 14.29% in wavefront-optimized group; P Z .04) is comparable to the results of Waring et al.8 in their series of 131 eyes having topography-guided LASIK using the Nidek CX II custom aspheric treatment zone (CATz) algorithm. They found that at 0.1 logMAR or better levels, the 6-month postoperative UDVA exceeded the preoperative CDVA in more than 25% of cases. A gain of 1 Snellen line of visual acuity over the preoperative CDVA was also seen in significantly more patients in the topography-guided group (28.47%) than in the wavefront-optimized group (17.14%) in our series (P Z .04). In a contralateral-eye comparison of topography-guided versus wavefront-optimized ablation, El Awady et al.15 reported similar results, with 19% of eyes in the topography-guided group and 12% of eyes in the wavefront-optimized group gaining 1 line of CDVA. In our study, predictability was similar between the 2 groups, with 94.3% of eyes in the topography-guided group and 85.71% of eyes in the wavefront-optimized group being within G0.5 D of emmetropia (P Z .09). Various studies14,17,20,21 have also reported a postoperative MRSE within G0.5 D of emmetropia in 75.0% to 96.1% cases after topography-guided ablation. This level of predictability for MRSE within G0.5 D of myopia seen with the topography-guided ablation in our series also compares favorably with the results reported by Kermani et al.17 (76%), Padmanabhan et al.22 (93%), and Moshirfar et al.23 (88%) for wavefrontguided treatments and by Padmanabhan et al.22 (89%) for wavefront-optimized treatments. El Awady et al.,15 in their contralateral-eye comparative study, found that vertical coma and higher cylindrical aberrations were lower in the topography-guided group than in the wavefront-optimized group. In the present series, the topography-guided profile induced significantly less coma and spherical aberration than the wavefront-optimized profile. Our results of topography-guided ablation are also similar to those of Du et al.,18 who found that HOAs were increased after LASIK regardless of whether the treatment was
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conventional or topography guided; however, the increase in HOAs after topography-guided ablation was less than that after conventional ablation. Spatial contrast sensitivity is a sensitive performance index of the functional quality of vision after refractive surgery because it assesses the combined effects of light scattering, optical aberrations, and defocus.24 In the present study, a significant drop was seen under the high-frequency (12 cpd and 18 cpd) mesopic testing conditions in both groups. Our results are consistent with those in a study by Montes-Mic o et al.,25 which found that LASIK induced significant reductions in contrast sensitivity under mesopic conditions at high spatial frequencies only, even though the photopic contrast sensitivity function was normal. However, the deterioration in our series was less in the topography-guided group than in the wavefront-optimized group, and the difference achieved statistical significance. It has been shown previously that induced changes in the contrast sensitivity function correlate significantly with increases in ocular HOAs (especially spherical aberration), which in turn are affected by the amount of stromal ablation.26 In our study, the topography-guided group had lower amounts of induced HOAs, including coma and spherical aberration, as well as less corneal ablation than the wavefront-optimized group, which might explain the better contrast sensitivity in the topography-guided group. In their series of topography-guided LASIK using the FACT, Dougherty et al.27 found a slight but significant gain in contrast under photopic and mesopic testing with glare at the lower frequencies (3 cpd and 6 cpd); whereas at 18 cpd under mesopic conditions, their results were similar to those in our study, with a significant drop from the preoperative levels (P Z .03). Another important outcome in the present study was that significantly less stromal tissue was ablated in the topography-guided group than in the wavefront-optimized group (mean 61.57 G 16.23 mm versus 79.71 G 14.81 mm; P ! .001), even though the refractive error to be corrected (ie, the preoperative MRSE) was slightly higher in the topography-guided group (mean 4.19 G 1.92 D in the topographyguided group versus 3.89 G 1.85 D in the wavefront-optimized group). This finding, if reproducible in other studies, could have significant clinical implications because saving corneal tissue can help expand the pool of candidates eligible for refractive surgery or the amount of refractive error that can be safely corrected. Outcomes obtained in the topography-guided group in the present study compare favorably with the results in the U.S. Food and Drug Administration (FDA)-approved multicenter topography-guided
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treatment study group.A The postoperative MRSE was within G0.5 D of plano and a postoperative UDVA of 0.0 logMAR or greater and 1 line gain of visual acuity over preoperative CDVA were achieved in 94.29%, 94.29%, and 28.57% of patients, respectively, in our series and in 94.8%, 92.6%, and 29.6% of patients, respectively, in the FDA trial. That mesopic contrast sensitivity at higher spatial frequencies (12 cpd and 18 cpd) deteriorated less in the topography-guided group than the wavefront-optimized group in our series might explain the improvement in visual symptoms (eg, difficulty in night driving, reading difficulty, and glare) that occurred in a significant number of patients in the postoperative period compared with preoperative levels with habitual correction in the FDA study. The better refractive and visual outcomes, lower induction of HOAs, and less tissue ablation in the topography-guided group compared with the wavefront-optimized group might be the outcome of the principles on which the Customized Refractive Surgery Master software topography-guided ablation algorithm is based. The algorithm uses the corneal wavefront data as well as the corneal elevation data to derive the ablation profile. Corneal regularization (performed to smoothen the subtle corneal irregularities present even in otherwise normal eyes) is based on elevation data. However, the target corneal surface is determined by analysis of the corneal wavefront data and the clinical manifest refraction. The topography-guided ablation profile is thus based on the individual corneal topography in which the excimer laser spots are targeted to flatten the peaks and steepen the flatter areas by ablating around them. This combined method of simultaneous hyperopic and myopic treatment removes much less tissue and still maintains the prolate shape of the cornea. In addition, the topography-guided ablation is centered on the corneal apex rather than the pupil center and hence also addresses the issue of angle k. Wavefrontoptimized ablations, on the other hand, derive the ablation pattern from population-based data for the correction of myopia and astigmatism and attempt to produce an aspheric profile by delivering more pulses to the peripheral cornea. Thus, wavefrontoptimized treatments are not individualized, and they are associated with more laser pulses leading to more tissue ablation and possibly with more sources of error. This might have caused a greater induction of HOAs in the postoperative period in eyes having wavefront-optimized treatment in our series. There were a few limitations in the present study. A subjective comparison of postoperative patient satisfaction relating to quality of vision and postoperative
symptoms such as glare or halos between the 2 eyes was not performed. Such data would help validate the objectively measured parameters and more effectively establish superiority, or lack thereof, of 1 technique over the other. The eyes were not stratified in terms of those having an HOA RMS less than or greater than 0.3 mm for intergroup comparison, and we also did not correlate changes in coma in eyes with a higher cylinder with those with a lower cylindrical component. Such stratification was beyond the scope of this study, although it could be a part of future studies. However, a major strength of this study was that because it was a contralateral-eye study, the confounding effect of varying wound healing and biomechanical properties of the cornea on the various parameters studied was avoided because fellow eyes of the same individual were generally accepted as having similar biomechanical characteristics and healing properties. The results in this study suggest a promising role for the more widespread use of topography-guided ablations in virgin eyes with myopia or myopic astigmatism. Future studies with a longer follow-up period might be useful to determine the effect of factors, such as changing lenticular aberrations, on the visual outcomes in patients who had topography-guided LASIK. WHAT WAS KNOWN Topography-guided LASIK, although mainly used for treating irregular corneas, has shown reasonably good visual and refractive outcomes when used as a primary treatment for correction of myopia and myopic astigmatism in virgin eyes. A previous study that compared wavefront-optimized LASIK with topography-guided LASIK did not find significant differences in the induced HOAs and the contrast sensitivity between these 2 groups. WHAT THIS PAPER ADDS Compared to wavefront-optimized LASIK, topographyguided LASIK induced a significantly lower amount of HOAs, especially coma and spherical aberrations, and was associated with better contrast sensitivity at high frequencies (12 cpd and 18 cpd) under mesopic testing conditions. Topography-guided LASIK resulted in significantly less stromal tissue ablation than wavefront-optimized LASIK. Topography-guided LASIK might be safely used as a primary treatment for myopia in virgin eyes as an alternative to wavefront-optimized LASIK.
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REFERENCES 1. Chalita MR, Chavala S, Xu M, Kreuger RR. Wavefront analysis in post-LASIK eyes and its correlation with visual symptoms, refraction, and topography. Ophthalmology 2004; 111:447–453 2. Mutyala S, McDonald MB, Scheinblum KA, Ostrick MD, Brint SF, Thompson H. Contrast sensitivity evaluation after laser in situ keratomileusis. Ophthalmology 2000; 107:1864–1867 3. Holladay JT, Janes JA. Topographic changes in corneal asphericity and effective optical zone after laser in situ keratomileusis. J Cataract Refract Surg 2002; 28:942–947 4. Moreno-Barriuso E, Merayo Lloves J, Marcos S, Navarro R, Llorente L, Barbero S. Ocular aberrations before and after myopic corneal refractive surgery: LASIK-induced changes measured with laser ray tracing. Invest Ophthalmol Vis Sci 2001; 42:1396–1403. Available at: http://iovs.arvojournals.org/ article.aspx?articleidZ2162653. Accessed July 17, 2016 5. Artal P, Navarro R. Monochromatic modulation transfer function of the human eye for different pupil diameters: an analytical expression. J Opt Soc Am A Opt Image Sci Vis 1994; 11:246– 249 6. Smadja D, Reggiani-Mello G, Santhiago MR, Krueger RR. Wavefront ablation profiles in refractive surgery: description, results, and limitations. J Refract Surg 2012; 28:224–232 € ffler J. Wavefront-opti€llner C, Lo 7. Mrochen M, Donitzky C, Wu mized ablation profiles: theoretical background. J Cataract Refract Surg 2004; 30:775–785 8. Waring G, Dougherty PJ, Chayet A, Fischer J, Fant B, Stevens G, Bains HS. Topographically guided LASIK for mopia using the Nidek CXII customized aspheric treatment zone (CATz). Trans Am Ophthalmol Soc 2007; 105:240–246; discussion 247–248 Available at: http://www.ncbi.nlm.nih.gov/pmc/ar ticles/PMC2258119/pdf/1545-6110_v105_p240.pdf. Accessed July 17, 2016 9. Knorz MC, Jendritza B. Topographically-guided laser in situ keratomileusis to treat corneal irregularities. Ophthalmology 2000; 107:1138–1143 10. Lin DY, Manche EE. Custom-contoured ablation pattern method for the treatment of decentered laser ablations. J Cataract Refract Surg 2004; 30:1675–1684 11. Kanellopoulos AJ. Comparison of sequential vs same-day simultaneous collagen cross-linking and topography-guided PRK for treatment of keratoconus. J Refract Surg 2009; 25:S812–S818 12. Cosar CB, Acar S. Topography-guided LASIK with the WaveLight laser after penetrating keratoplasty. J Refract Surg 2006; 22:716–719 13. Lee D-H, Seo SJ, Shin S-C. Topography-guided excimer laser ablation of irregular cornea resulting from penetrating injury. J Cataract Refract Surg 2002; 28:186–188 14. Tan J, Simon D, Mrochen M, Por YM. Clinical results of topography-based customized ablations for myopia and myopic astigmatism. J Refract Surg 2012; 28:S829–S836 15. El Awady HE, Ghanem AA, Saleh SM. Wavefront-optimized ablation versus topography-guided customized ablation in myopic LASIK: comparative study of higher order aberrations. Ophthalmic Surg Lasers Imaging 2011; 42:314–320 16. Kanjani N, Jacob S, Agarwal A, Agarwal A, Agarwal S, Agarwal T, Doshi A, Doshi S. Wavefront- and topographyguided ablation in myopic eyes using Zyoptix. J Cataract Refract Surg 2004; 30:398–402
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17. Kermani O, Schmiedt K, Oberheide U, Gerten G. Topographicand wavefront-guided customized ablations with the NIDEKEC5000CXII in LASIK for myopia. J Refract Surg 2006; 22:754–763 18. Du C-X, Yang Y-B, Shen Y, Wang Y, Dougherty PJ. Bilateral comparison of conventional versus topographic-guided customized ablation for myopic LASIK with the NIDEK EC-5000. J Refract Surg 2006; 22:642–646 19. Farooqui MA, Al-Muammar AR. Topography-guided CATz versus conventional LASIK for myopia with the NIDEK EC5000: a bilateral eye study. J Refract Surg 2006; 22:741–745 20. Knorz MC, Neuhann T. Treatment of myopia and myopic astigmatism by customized laser in situ keratomileusis based on corneal topography. Ophthalmology 2000; 107:2072–2076; discussion by RS Rubinfeld, 2076 21. Cummings AB, Mascharka N. Outcomes after topographybased LASIK and LASEK with the WaveLight Oculyzer and Topolyzer platforms. J Refract Surg 2010; 26:478–485 22. Padmanabhan P, Mrochen M, Basuthkar S, Viswanathan D, Joseph R. Wavefront-guided versus wavefront-optimized laser in situ keratomileusis: contralateral comparative study. J Cataract Refract Surg 2008; 34:389–397 23. Moshirfar M, Schliesser JA, Chang JC, Oberg TJ, Mifflin MD, Townley R, Livingston MK, Kurz CJ. Visual outcomes after wavefront-guided photorefractive keratectomy and wavefrontguided laser in situ keratomileusis: prospective comparison. J Cataract Refract Surg 2010; 36:1336–1343 s-Mico R, Charman WN. Choice of spatial frequency for 24. Monte contrast sensitivity evaluation after corneal refractive surgery. J Refract Surg 2001; 17:646–651 s-Mico R, Espan ~ a E, Menezo JL. Mesopic contrast sensi25. Monte tivity function after laser in situ keratomileusis. J Refract Surg 2003; 19:353–356 26. Yamane N, Miyata K, Samejima T, Hiraoka T, Kiuchi T, Okamoto F, Hirohara Y, Mihashi T, Oshika T. Ocular higherorder aberrations and contrast sensitivity after conventional laser in situ keratomileusis. Invest Ophthalmol Vis Sci 2004; 45:3986–3990. Available at: http://iovs.arvojournals.org/article. aspx?articleidZ2124587. Accessed July 17, 2016 27. Dougherty PJ, Waring G III, Chayet A, Fischer J, Fant B, Bains HS. Topographically guided laser in situ keratomileusis for myopia using a customized aspherical treatment zone. J Cataract Refract Surg 2008; 34:1862–1871
OTHER CITED MATERIAL A. U.S. Food and Drug Administration. Summary of Safety and Effectiveness Data [for the ALLEGRETTO WAVEÒ Eye-Q Excimer Laser]. PMA P020050/S12, September 27, 2013; page 5. Available at: http://www.accessdata.fda.gov/cdrh_docs/ pdf2/p020050s012b.pdf. Accessed July 17, 2016
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First author: Arun Kumar Jain, MD, DNB Advanced Eye Centre, Post Graduate Institute of Medical Education and Research, Chandigarh, India
Outcomes of topography-guided versus wavefront-optimized laser in situ keratomileusis for myopia in virgin eyes Arun Kumar Jain, MD, DNB, Chintan Malhotra, MS, Anand Pasari, MS, Pawan Kumar, BSc, Majid Moshirfar, MD
PURPOSE: To compare the outcomes of topography-guided and wavefront-optimized treatment in patients having laser in situ keratomileusis (LASIK) for myopia. SETTING: Advanced Eye Centre, Post Graduate Institute of Medical Education and Research, Chandigarh, India. DESIGN: Prospective contralateral-eye case study. METHODS: Patients had topography-guided LASIK in 1 eye and wavefront-optimized LASIK in the contralateral eye using the Customized Refractive Surgery Master software and Mel 80 excimer laser. Refractive (residual manifest refraction spherical equivalent [MRSE], higher-order aberrations [HOAs]), and visual (uncorrected distance visual acuity [UDVA] and photopic and mesopic contrast sensitivity) outcomes were prospectively analyzed 6 months postoperatively. RESULTS: The study comprised 35 patients. The UDVA was 0.0 logMAR or better and the postoperative residual MRSE was G0.50 diopter in 94.29% of eyes in the topography-guided group and 85.71% of eyes in the wavefront-optimized group (P Z .09). More eyes in the topography-guided group than in the wavefront-optimized group had a UDVA of 0.1 logMAR or better (P Z .04). Topography-guided LASIK was associated with less deterioration of mesopic contrast sensitivity at higher spatial frequencies (12 cycles per degree [cpd] and 18 cpd) and lower amounts of induced coma (P Z .04) and spherical aberration (P Z .04). Less stromal tissue was ablated in the topography-guided group (mean 61.57 mm G 16.23 [SD]) than in the wavefront-optimized group (mean 79.71 G 14.81 mm) (P < .001). CONCLUSION: Although topography-guided LASIK and wavefront-optimized LASIK gave excellent results, topography-guided LASIK was associated with better contrast sensitivity, lower induction of HOAs, and a smaller amount of tissue ablation. Financial Disclosure: None of the authors has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2016; 42:1302–1311 Q 2016 ASCRS and ESCRS
Because of its efficacy and safety, laser in situ keratomileusis (LASIK) is one of the most popular procedures for the correction of refractive errors. However, there has always been a subset of patients who remain dissatisfied postoperatively because of side effects such as glare, halos, starbursts and reduced contrast sensitivity.1,2 This has been attributed in part to the ablation profile of conventional LASIK, which causes significant induction of positive spherical aberration and other higher-order aberrations (HOAs).3,4 These in turn are known to be associated with a deterioration 1302
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in the point-spread function and modulation transfer function of the eye, manifesting clinically as a deterioration in visual quality.5 Different ablation profiles have been developed over the years in an attempt to overcome these undesirable postoperative symptoms. These include wavefront-optimized, wavefront-guided, and topography-guided ablation profiles.6 The wavefrontoptimized profile is designed to limit the induction of a positive spherical aberration without specifically targeting the preexisting patterns of HOAs in the http://dx.doi.org/10.1016/j.jcrs.2016.06.035 0886-3350
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eye by delivering an increased number of laser pulses to the corneal periphery rather than the center, which helps maintain the prolate shape of cornea postoperatively.7 The topography-guided ablation algorithm, in addition to treating spherocylindric refractive errors (ie, the lower-order aberrations [LOAs]), addresses the irregularities of the corneal elevation in an effort to reshape the cornea into an ideal curve and achieve a planar wavefront postoperatively.8 Unlike the wavefront-guided profiles, the topography-guided ablation profiles do not attempt to correct the aberrations arising from the crystalline lens or other ocular structures. Although traditionally topographic treatments have been used to treat irregular corneas,9–13 studies have also documented their safety and efficacy in the treatment of primary myopia and astigmatism.14–19 All these ablation profiles have been widely used in refractive procedures; however, no treatment algorithm has shown definite clinical superiority over others with regard to visual acuity and correction of LOAs.7 The lack of direct comparisons between wavefront-optimized and topography-guided treatment using the Mel 80 excimer laser (Carl Zeiss Meditec AG) and the paucity of contralateral-eye studies prompted this prospective study to compare the efficacy and safety of the more commonly performed wavefront-optimized ablation profile with the topography-guided ablation profile for the treatment of myopia or myopic astigmatism in virgin eyes having LASIK. PATIENTS AND METHODS This prospective comparative contralateral-eye study included patients having LASIK for the correction of myopia or myopic astigmatism at the Cornea and Refractive
Submitted: December 11, 2015. Final revision submitted: May 24, 2016. Accepted: June 29, 2016. From the Advanced Eye Centre (Jain, Malhotra, Parasi, Kumar), Post Graduate Institute of Medical Education and Research, Chandigarh, India; the Department of Ophthalmology (Moshirfar), Francis I. Proctor Foundation, University of California San Francisco, San Francisco, California, USA. Presented in part at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, April 2015, and the VII World Cornea Congress, San Diego, California, USA, April 2015. Corresponding author: Arun Kumar Jain, MD, DNB, Room No 110, Advanced Eye Centre, Post Graduate Institute of Medical Education and Research, Sector 12, Chandigarh 160012, India. E-mail: [email protected].
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Services, Advanced Eye Centre, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India, between July 2013 and February 2014. Patients were enrolled after signing an informed consent form. The study was approved by the Institutional Review Board of PGIMER and adhered to the tenets of Declaration of Helsinki. For randomization, a coin toss was used to determine the treatment algorithm for the right eye of each patient; wavefront-optimized treatment was performed if the toss was a heads up, and topography-guided treatment was performed if the toss resulted in a tails up. The left eye had the opposite treatment algorithm. Inclusion criteria for the study were age 18 years to 35 years, stable refractive error with 0.50 to 6.00 diopters (D) of spherical myopia, astigmatism between 0.00 D and 3.50 D, maximum manifest spherical equivalent of 6.00 D, and distance visual acuity correctable to 0.0 logMAR or better. Exclusion criteria were presence of significant dry eye, anterior segment abnormalities (ie, cataracts, corneal scarring, or neovascularization within 1.0 mm of intended ablation zone), basement membrane disease, history of recurrent corneal erosions, progressive or unstable myopia, estimated postoperative residual stromal bed thickness of less than 250 mm, established or forme fruste keratoconus, macular or retinal disease, current use of systemic corticosteroid or immunosuppressive therapy, autoimmune disease, collagen vascular disease, diabetes mellitus, pregnancy, and lactation. The preoperative examination for each patient included uncorrected distance visual acuity (UDVA) using a standard Snellen eye chart, corrected distance visual acuity (CDVA) (with spectacles), manifest refraction, cycloplegic refraction with cyclopentolate 1.0%, postmydriatic testing at least 72 hours after cycloplegic refraction, intraocular pressure measurements, slitlamp biomicroscopy of the anterior segment, dilated fundus evaluation, Scheimpflug imaging with the Pentacam HR device (Oculus Surgical, Inc.), combined corneal topography and corneal wavefront analysis with the Atlas 9000 corneal topographer (Carl Zeiss Meditec AG), whole-eye wavefront analysis with the Wasca wavefront aberration–supported cornea ablation aberrometer (Carl Zeiss Meditec AG), and contrast sensitivity measurements (performed unioculary under photopic and mesopic conditions) with the Functional Vision Analyzer (Stereo Optical Co., Inc.). Contact lens users were asked to discontinue lens wear 2 weeks before screening for soft contact lenses and 6 weeks before screening for rigid gas-permeable contact lenses. Manifest refraction and wavefront measurements were repeated at 2 visits to ensure refractive stability. Eligible patients were scheduled for simultaneous bilateral LASIK, wavefront-optimized in 1 eye and topographyguided in the contralateral eye. The correction target was based on the manifest refraction, with emmetropia being the target in all patients. An Intralase FS 150 Hz femtosecond laser (Abbott Medical Optics, Inc.) was used for flap creation and an Mel 80 excimer laser for ablation in all eyes. The same surgeon (A.K.J.) performed all the LASIK procedures. The flap diameter varied from 8.5 to 9.5 mm, with a programmed thickness between 90 mm and 110 mm. Postoperatively, the patients were examined at 1 day, 1 week, 1 month, 3 months, and 6 months. All postoperative follow-up visits included measurement of UDVA, CDVA (if indicated), wavefront aberration–supported cornea ablation aberrometry, corneal topography using the same topographer as preoperatively, and the Functional Acuity Contrast Test (FACT).
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Device Technology
Refractive and Visual Outcomes
Customized Refractive Surgery Master software (Carl Zeiss Meditec AG) was locally networked with the Atlas topographer (which uses Placido disk technology) and the Wasca wavefront aberration–supported cornea ablation analyzer (a high-resolution Hartmann-Shack aberrometer), thus enabling integration of topographic and wavefront data. With this setup, aspheric spherocylindrical refractive ablations (wavefront-optimized ablations) are generated using manifest refraction values entered manually. Two aspheric profiles are available. One is designed to reduce the ablation depth in borderline corneas, and the other is optimized for asphericity. The corneal topography–based ablation algorithms use topographic and corneal elevation data and can be applied in the following ways: (1) as a purely topographic smoothening algorithm for conditions such as small optic zones, decentered ablations, or irregular astigmatism, where the aim is to correct the corneal irregularity without targeting the spherocylindrical error (the limit for the asymmetric ablation being 50 mm), or (2) as a topographic refractive algorithm, which simultaneously corrects the refractive error and also smoothens the cornea, thus targeting maintenance of corneal asphericity and minimal induction of HOAs. Except for the 2 treatment algorithms (ie, wavefrontoptimized or topography-guided) no nomogram correction was performed for either arm of the study, the rationale being that nomogram adjustment is required for treating highly irregular corneas, for which the topographysmooth ablation profile is used first to normalize the cornea without targeting the LOAs of sphere and cylinder. However, this ablation itself induces changes in LOAs and hence necessitates nomogram adjustment. Because virgin myopic eyes without significant corneal irregularities were included in the present study, no additional nomogram adjustment was performed.
Figure 1 shows the refractive and visual outcomes in the topography-guided group and Figure 2, in the wavefront-optimized group.
Statistical Analysis The continuous data are presented as the mean G SD or the median and interquartile range, as appropriate. The normality of quantitative data was checked by measures of Kolmogorov-Smirnov tests. The Mann-Whitney U test was used for statistical analysis of skewed continuous variables. For normally distributed data, the t test was used to compare the 2 treatment groups. For time-related and repeated measures of HOAs, 1-way analysis of variance followed by Bonferroni correction for multiple comparisons were used. The qualitative or categorical variables were described as frequencies and proportions. The proportions were compared using the chi-square or Fisher exact test, whichever was applicable. A P value less than 0.05 was considered to indicate statistical significance. All calculations were performed using SPSS software (version 20, SPSS, Inc.).
Efficacy Both procedures were equally efficacious at the end of the 6-month follow-up, with a mean efficacy index (ratio of postoperative decimal UDVA to preoperative decimal CDVA) of 1.013 G 0.12 (SD) in the wavefrontoptimized group and 1.053 G 0.11 in the topographyguided group (P Z .151). Thirty-three eyes (94.3%) in the topography-guided group and 30 eyes (85.71%) in the wavefront-optimized group had a UDVA of 0.0 logMAR (20/20) or better (P Z .09) at the end of 6 months. A significantly greater proportion of eyes in the topography-guided group (10 eyes [28.57%]) than the wavefront-optimized group (5 eyes [14.29%]) had a UDVA better than 0.1 logMAR (20/16) (P Z .04). Safety The 2 ablation profiles had similar safety profiles. The mean safety index (ratio of mean preoperative decimal CDVA to mean postoperative decimal CDVA) at 6 months was 1.054 G 0.09 in the wavefront-optimized group and 1.089 G 0.10 in the topography-guided group (P Z .128). No patient in either group had lost lines of CDVA at the end of 6 months. The CDVA was 0.0 logMAR or better in all eyes in each group. Predictability The mean manifest refraction spherical equivalent (MRSE) 6 months postoperatively was 0.17 G 0.38 D (range 1.12 to 0.62 D) and 0.02 G 0.29 D (range 0.87 to 1.00 D) in the wavefront-optimized group and topography-guided group, respectively (P Z .022). Both ablation profiles had similar predictability for MRSE within G1.0 D of emmetropia (P Z .15) and for MRSE within G0.5 D of emmetropia (P Z .09). Stability
RESULTS
Stability was similar in the 2 groups, with 4 eyes (11.42%) in the wavefront-optimized group and 2 eyes (5.71%) in the topography-guided group having an MRSE change of more than 0.5 D from 3 to 6 months postoperatively (P Z .22).
The study comprised 35 patients (70 eyes; 35 in each treatment group). Table 1 compares the preoperative and intraoperative parameters between the wavefront-optimized group and the topography-guided group.
Higher-Order Aberrations Preoperatively, ocular (whole-eye) HOAs and corneal HOAs at a 6.0 mm pupil diameter were comparable between the 2 groups (Table 2). At 6 months,
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Table 1. Between-group comparison of preoperative characteristics and intraoperative parameters. Mean G SD Parameter Sphere (D) Cylinder (D) MRSE (D) Pachymetry (mm) Flat keratometry (D) Steep keratometry (D) Optical zone (mm) Ablation depth (mm) RSB (mm)
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
3.98 G 1.24 0.29 G 0.42 3.89 G 1.85 542.20 G 23.86 43.49 G 2.41 44.02 G 1.58 6.21 G 0.15 79.71 G 14.81 361.46 G 31.46
4.19 G 1.30 0.30 G 0.38 4.19 G 1.92 540.70 G 25.38 43.39 G 1.48 43.82 G 1.52 6.28 G 0.14 61.57 G 16.23 373.69 G 34.27
.600 .596 .817 .955 .404 .482 .109 !.001* .125
MRSE Z manifest refraction spherical equivalent; RSB Z residual stromal bed; TG Z topography-guided; WFO Z wavefront-optimized *Statistically significant (P ! .05)
there was a statistically significant induction of a majority of the ocular HOAs (wavefront aberration–supported cornea ablation aberrometry), including total HOA, coma, and spherical aberration, in both groups when compared with the preoperative values (Table 3). Topography-guided ablation induced significantly lower coma (P Z .043) and spherical aberrations (P Z .04) than
wavefront-optimized ablation (Table 3). At all timepoints when HOAs were measured postoperatively, the majority of the ocular HOAs, including the total HOA root mean square (RMS), coma, and spherical aberrations, were lower in the topography-guided group than in the wavefront-optimized group, whereas trefoil was comparable between the 2 groups (Figure 3).
Figure 1. Refractive and visual outcomes in the topography-guided group (CDVA Z corrected distance visual acuity; UDVA Z uncorrected distance visual acuity; VA Z visual acuity). J CATARACT REFRACT SURG - VOL 42, SEPTEMBER 2016
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Figure 2. Refractive and visual outcomes in the wavefront-optimized group (CDVA Z corrected distance visual acuity; UDVA Z uncorrected distance visual acuity; VA Z visual acuity).
Contrast Sensitivity
within-group comparison showed no significant deterioration in contrast sensitivity under photopic conditions in either group. Testing under mesopic conditions showed significant deterioration at 12 cycles per degree (cpd) and 18 cpd in both groups compared with the preoperative levels (Figure 4).
The preoperative contrast sensitivity was similar in the wavefront-optimized group and the topographyguided group at each spatial frequency tested and under photopic conditions and mesopic conditions (Table 4). Six months after surgery, the
Table 2. Between-group comparison of preoperative ocular and corneal HOAs. Mean RMS Value (mm) G SD Preoperative Ocular HOAs (Aberrometry) Parameter Total HOAs 3rd order 4th order Coma Trefoil SA Sec astg Tetrafoil
Preoperative Corneal HOAs (Topography)
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
0.74 G 0.25 0.62 G 0.29 0.36 G 0.10 0.37 G 0.27 0.45 G 0.26 0.16 G 0.11 0.20 G 0.09 0.21 G 0.09
0.75 G 0.29 0.62 G 0.24 0.39 G 0.21 0.42 G 0.23 0.40 G 0.24 0.21 G 0.15 0.22 G 0.19 0.19 G 0.12
.904 .961 .349 .403 .427 .115 .547 .401
0.40 G 0.09 0.25 G 0.07 0.30 G 0.07 0.20 G 0.08 0.13 G 0.06 0.28 G 0.08 0.06 G 0.02 0.08 G 0.04
0.37 G 0.03 0.23 G 0.04 0.28 G 0.03 0.17 G 0.08 0.13 G 0.05 0.27 G 0.06 0.06 G 0.03 0.04 G 0.02
.223 .327 .446 .114 .148 .887 .892 .096
HOAs Z higher-order aberrations; RMS Z root mean square; SA Z spherical aberration; Sec astg Z secondary astigmatism; TG Z topography-guided; WFO Z wavefront-optimized
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Table 3. Comparison of within-group preoperative and 6-month postoperative ocular HOAs (aberrometry) and between-group comparisons of magnitude of surgically induced aberrations. Mean RMS Value (mm) G SD WFO Group Parameter Total HOAs 3rd order 4th order Coma Trefoil SA Sec astg Tetrafoil
TG Group
Magnitude of Surgically Induced HOAs
Preop (n Z 35) Postop (n Z 35) P Value Preop (n Z 35) Postop (n Z 35) P Value WFO Group 0.74 G 0.25 0.62 G 0.29 0.36 G 0.10 0.37 G 0.27 0.45 G 0.26 0.16 G 0.11 0.20 G 0.09 0.21 G 0.09
1.17 G 0.45 0.97 G 0.41 0.63 G 0.27 0.87 G 0.41 0.38 G 0.28 0.54 G 0.29 0.17 G 0.10 0.20 G 0.10
.001* .004* !.001* !.001* .121 !.001* .135 .223
0.75 G 0.29 0.62 G 0.24 0.39 G 0.21 0.42 G 0.23 0.40 G 0.24 0.21 G 0.15 0.22 G 0.19 0.19 G 0.12
1.07 G 0.38 0.88 G 0.39 0.57 G 0.24 0.71 G 0.44 0.35 G 0.33 0.48 G 0.27 0.18 G 0.11 0.15 G 0.09
.012* .029* .049* .036* .466 .001* .317 .091
0.43 0.35 0.2 0.50 0.07 0.38 0.03 0.01
TG Group 0.32 0.26 0.28 0.29 0.05 0.27 0.04 0.04
P Value .34 .46 .63 .043* .92 .04* .63 .70
HOAs Z higher order aberrations; RMS Z root mean square; SA Z spherical aberration; Sec astg Z secondary astigmatism; TG Z topography-guided; WFO Z wavefront-optimized *Statistically significant (P ! .05)
Intergroup comparison at 6 months showed that although the decrease in postoperative photopic contrast sensitivity at all tested frequencies was comparable in the 2 groups, mesopic contrast sensitivity
at the higher spatial frequencies (ie, 12 cpd and 18 cpd) had deteriorated significantly less in the topography-guided group than in the wavefrontoptimized group (Figure 5).
Figure 3. Comparison of wavefront-optimized LASIK and topography-guided LASIK with respect to induced ocular HOAs in the postoperative period (HOAs Z higher-order aberrations; RMS Z root mean square; TG Z topography guided; WFO Z wavefront optimized). J CATARACT REFRACT SURG - VOL 42, SEPTEMBER 2016
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Table 4. Intergroup comparison of preoperative photopic and mesopic contrast sensitivity on FACT (log units). Photopic Contrast Sensitivity (85 cd/m2) Frequency (Cpd) 1.5 3.0 6.0 12.0 18.0
Mesopic Contrast Sensitivity (3 cd/m2)
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
WFO Group (n Z 35)
TG Group (n Z 35)
P Value
1.58 1.99 1.93 1.63 0.81
1.6 1.97 1.92 1.64 0.8
.547 .547 .731 .717 .697
1.57 1.95 1.81 1.43 0.72
1.56 1.95 1.82 1.44 0.74
.797 .732 .868 .827 .369
cd Z candelas; Cpd Z cycles per degree; TG Z topography-guided; WFO Z wavefront-optimized
DISCUSSION Expectations for the outcomes of refractive surgery are increasing progressively, with patients wanting not only spectacle independence but also excellent visual
Figure 4. Comparison of preoperative and 6-month postoperative photopic and mesopic contrast sensitivity in each group (* Z statistically significant [P ! .05]; cpd Z cycles per degree; TG Z topography guided; WFO Z wavefront optimized).
quality and increased safety. Attempts to address preexisting HOAs by wavefront-guided or topographyguided treatments are steps in this direction. Compared with wavefront measurement with aberrometers, topographic measurements from the corneal surface can measure more points, including those in the corneal periphery, which is where most of the aberrations lie. Also, corneal topography, unlike wavefront data, is unaffected by factors such as pupil size, accommodative status of the eye (which itself can induce some spherical refractive changes and HOAs), and centroid shift or by internal optical components such as early cataract. This makes the topographically acquired data a far more stable parameter than the wavefront data. In addition, topographic measurements can be used in highly aberrated eyes for which wavefront data might be unreliable. However, unlike wavefront analyzers, topographers do not provide information about the spherocylindrical refraction of the eye. Hence, topographic refractive treatment algorithms should be combined with measurements obtained from manifest refraction rather than based on
Figure 5. Comparison of wavefront-optimized LASIK and topography-guided LASIK with respect to 6-month postoperative photopic and mesopic contrast sensitivity (* Z statistically significant [P ! .05]; cpd Z cycles per degree; TG Z topography guided; WFO Z wavefront optimized).
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information acquired by the topographer alone. A potential concern with topography-guided treatments might be that treating only the corneal aberrations could unmask some lenticular HOAs (which in the virgin eye are usually balanced by HOAs arising from the cornea up to approximately age 30 years), thus leading to a less favorable ablation profile with reduced quality of vision postoperatively. In the present study, the LASIK outcomes in the topography-guided group were better than or equivalent to those in the wavefront-optimized group for the various parameters analyzed. The number of patients achieving a postoperative UDVA of 0.1 logMAR (28.57% in topography-guided group versus 14.29% in wavefront-optimized group; P Z .04) is comparable to the results of Waring et al.8 in their series of 131 eyes having topography-guided LASIK using the Nidek CX II custom aspheric treatment zone (CATz) algorithm. They found that at 0.1 logMAR or better levels, the 6-month postoperative UDVA exceeded the preoperative CDVA in more than 25% of cases. A gain of 1 Snellen line of visual acuity over the preoperative CDVA was also seen in significantly more patients in the topography-guided group (28.47%) than in the wavefront-optimized group (17.14%) in our series (P Z .04). In a contralateral-eye comparison of topography-guided versus wavefront-optimized ablation, El Awady et al.15 reported similar results, with 19% of eyes in the topography-guided group and 12% of eyes in the wavefront-optimized group gaining 1 line of CDVA. In our study, predictability was similar between the 2 groups, with 94.3% of eyes in the topography-guided group and 85.71% of eyes in the wavefront-optimized group being within G0.5 D of emmetropia (P Z .09). Various studies14,17,20,21 have also reported a postoperative MRSE within G0.5 D of emmetropia in 75.0% to 96.1% cases after topography-guided ablation. This level of predictability for MRSE within G0.5 D of myopia seen with the topography-guided ablation in our series also compares favorably with the results reported by Kermani et al.17 (76%), Padmanabhan et al.22 (93%), and Moshirfar et al.23 (88%) for wavefrontguided treatments and by Padmanabhan et al.22 (89%) for wavefront-optimized treatments. El Awady et al.,15 in their contralateral-eye comparative study, found that vertical coma and higher cylindrical aberrations were lower in the topography-guided group than in the wavefront-optimized group. In the present series, the topography-guided profile induced significantly less coma and spherical aberration than the wavefront-optimized profile. Our results of topography-guided ablation are also similar to those of Du et al.,18 who found that HOAs were increased after LASIK regardless of whether the treatment was
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conventional or topography guided; however, the increase in HOAs after topography-guided ablation was less than that after conventional ablation. Spatial contrast sensitivity is a sensitive performance index of the functional quality of vision after refractive surgery because it assesses the combined effects of light scattering, optical aberrations, and defocus.24 In the present study, a significant drop was seen under the high-frequency (12 cpd and 18 cpd) mesopic testing conditions in both groups. Our results are consistent with those in a study by Montes-Mic o et al.,25 which found that LASIK induced significant reductions in contrast sensitivity under mesopic conditions at high spatial frequencies only, even though the photopic contrast sensitivity function was normal. However, the deterioration in our series was less in the topography-guided group than in the wavefront-optimized group, and the difference achieved statistical significance. It has been shown previously that induced changes in the contrast sensitivity function correlate significantly with increases in ocular HOAs (especially spherical aberration), which in turn are affected by the amount of stromal ablation.26 In our study, the topography-guided group had lower amounts of induced HOAs, including coma and spherical aberration, as well as less corneal ablation than the wavefront-optimized group, which might explain the better contrast sensitivity in the topography-guided group. In their series of topography-guided LASIK using the FACT, Dougherty et al.27 found a slight but significant gain in contrast under photopic and mesopic testing with glare at the lower frequencies (3 cpd and 6 cpd); whereas at 18 cpd under mesopic conditions, their results were similar to those in our study, with a significant drop from the preoperative levels (P Z .03). Another important outcome in the present study was that significantly less stromal tissue was ablated in the topography-guided group than in the wavefront-optimized group (mean 61.57 G 16.23 mm versus 79.71 G 14.81 mm; P ! .001), even though the refractive error to be corrected (ie, the preoperative MRSE) was slightly higher in the topography-guided group (mean 4.19 G 1.92 D in the topographyguided group versus 3.89 G 1.85 D in the wavefront-optimized group). This finding, if reproducible in other studies, could have significant clinical implications because saving corneal tissue can help expand the pool of candidates eligible for refractive surgery or the amount of refractive error that can be safely corrected. Outcomes obtained in the topography-guided group in the present study compare favorably with the results in the U.S. Food and Drug Administration (FDA)-approved multicenter topography-guided
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treatment study group.A The postoperative MRSE was within G0.5 D of plano and a postoperative UDVA of 0.0 logMAR or greater and 1 line gain of visual acuity over preoperative CDVA were achieved in 94.29%, 94.29%, and 28.57% of patients, respectively, in our series and in 94.8%, 92.6%, and 29.6% of patients, respectively, in the FDA trial. That mesopic contrast sensitivity at higher spatial frequencies (12 cpd and 18 cpd) deteriorated less in the topography-guided group than the wavefront-optimized group in our series might explain the improvement in visual symptoms (eg, difficulty in night driving, reading difficulty, and glare) that occurred in a significant number of patients in the postoperative period compared with preoperative levels with habitual correction in the FDA study. The better refractive and visual outcomes, lower induction of HOAs, and less tissue ablation in the topography-guided group compared with the wavefront-optimized group might be the outcome of the principles on which the Customized Refractive Surgery Master software topography-guided ablation algorithm is based. The algorithm uses the corneal wavefront data as well as the corneal elevation data to derive the ablation profile. Corneal regularization (performed to smoothen the subtle corneal irregularities present even in otherwise normal eyes) is based on elevation data. However, the target corneal surface is determined by analysis of the corneal wavefront data and the clinical manifest refraction. The topography-guided ablation profile is thus based on the individual corneal topography in which the excimer laser spots are targeted to flatten the peaks and steepen the flatter areas by ablating around them. This combined method of simultaneous hyperopic and myopic treatment removes much less tissue and still maintains the prolate shape of the cornea. In addition, the topography-guided ablation is centered on the corneal apex rather than the pupil center and hence also addresses the issue of angle k. Wavefrontoptimized ablations, on the other hand, derive the ablation pattern from population-based data for the correction of myopia and astigmatism and attempt to produce an aspheric profile by delivering more pulses to the peripheral cornea. Thus, wavefrontoptimized treatments are not individualized, and they are associated with more laser pulses leading to more tissue ablation and possibly with more sources of error. This might have caused a greater induction of HOAs in the postoperative period in eyes having wavefront-optimized treatment in our series. There were a few limitations in the present study. A subjective comparison of postoperative patient satisfaction relating to quality of vision and postoperative
symptoms such as glare or halos between the 2 eyes was not performed. Such data would help validate the objectively measured parameters and more effectively establish superiority, or lack thereof, of 1 technique over the other. The eyes were not stratified in terms of those having an HOA RMS less than or greater than 0.3 mm for intergroup comparison, and we also did not correlate changes in coma in eyes with a higher cylinder with those with a lower cylindrical component. Such stratification was beyond the scope of this study, although it could be a part of future studies. However, a major strength of this study was that because it was a contralateral-eye study, the confounding effect of varying wound healing and biomechanical properties of the cornea on the various parameters studied was avoided because fellow eyes of the same individual were generally accepted as having similar biomechanical characteristics and healing properties. The results in this study suggest a promising role for the more widespread use of topography-guided ablations in virgin eyes with myopia or myopic astigmatism. Future studies with a longer follow-up period might be useful to determine the effect of factors, such as changing lenticular aberrations, on the visual outcomes in patients who had topography-guided LASIK. WHAT WAS KNOWN Topography-guided LASIK, although mainly used for treating irregular corneas, has shown reasonably good visual and refractive outcomes when used as a primary treatment for correction of myopia and myopic astigmatism in virgin eyes. A previous study that compared wavefront-optimized LASIK with topography-guided LASIK did not find significant differences in the induced HOAs and the contrast sensitivity between these 2 groups. WHAT THIS PAPER ADDS Compared to wavefront-optimized LASIK, topographyguided LASIK induced a significantly lower amount of HOAs, especially coma and spherical aberrations, and was associated with better contrast sensitivity at high frequencies (12 cpd and 18 cpd) under mesopic testing conditions. Topography-guided LASIK resulted in significantly less stromal tissue ablation than wavefront-optimized LASIK. Topography-guided LASIK might be safely used as a primary treatment for myopia in virgin eyes as an alternative to wavefront-optimized LASIK.
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First author: Arun Kumar Jain, MD, DNB Advanced Eye Centre, Post Graduate Institute of Medical Education and Research, Chandigarh, India