Journal of Refractive Surgery

Original Article 

A Randomized Comparative Study of Topography-Guided Versus Wavefront-Optimized FS-LASIK for Correcting Myopia and Myopic Astigmatism

Yu Zhang, MD; Yueguo Chen, MD

Abstract

PURPOSE:

To compare clinical outcomes between topography-guided customized ablation treatment (TCAT) and wavefront-optimized (WFO) laser in situ keratomileusis (LASIK) in fellow eyes of myopic patients.

METHODS:

This prospective randomized contralateral study included 432 eyes of 216 myopic patients who underwent LASIK. TCAT was randomly performed in one eye (TCAT group) and WFO LASIK in the fellow eye (WFO group). The WaveLight FS200 femtosecond laser (Alcon Laboratories, Inc., Fort Worth, TX) was used to create the flap and the EX500 excimer laser was used for photoablation. The Sirius combined corneal topographer and tomographer system (CSO, Florence, Italy) was used to measure the corneal aberrations. Refractive and visual outcomes and corneal aberrations were compared between the two groups.

RESULTS:

At 1 month postoperatively, the uncorrected distance visual acuity (UDVA) was 20/20 or better in 89.4% of eyes in the TCAT group and 93.5% of eyes in the WFO group (P < .05). The UDVA became similar at postoperative 6 months (P > .05). Postoperative corrected distance visual acuity and residual manifest refractive spherical equivalent were similar between the groups (P > .05). The postoperative residual refractive astigmatism in the TCAT group was greater than that in the WFO group (P < .05). The optical path difference and root mean square of higher order aberrations and coma were significantly lower in eyes in the TCAT group at postoperative 1 and 6 months (P < .05).

CONCLUSIONS:

TCAT in virgin eyes induced less corneal optical path difference, fewer higher order aberrations, and less coma than WFO LASIK. However, TCAT was not as accurate as WFO, especially in astigmatism correction. A better compensation method for TCAT is warranted.

[J Refract Surg. 2019;35(9):575–582.]

Abstract

PURPOSE:

To compare clinical outcomes between topography-guided customized ablation treatment (TCAT) and wavefront-optimized (WFO) laser in situ keratomileusis (LASIK) in fellow eyes of myopic patients.

METHODS:

This prospective randomized contralateral study included 432 eyes of 216 myopic patients who underwent LASIK. TCAT was randomly performed in one eye (TCAT group) and WFO LASIK in the fellow eye (WFO group). The WaveLight FS200 femtosecond laser (Alcon Laboratories, Inc., Fort Worth, TX) was used to create the flap and the EX500 excimer laser was used for photoablation. The Sirius combined corneal topographer and tomographer system (CSO, Florence, Italy) was used to measure the corneal aberrations. Refractive and visual outcomes and corneal aberrations were compared between the two groups.

RESULTS:

At 1 month postoperatively, the uncorrected distance visual acuity (UDVA) was 20/20 or better in 89.4% of eyes in the TCAT group and 93.5% of eyes in the WFO group (P < .05). The UDVA became similar at postoperative 6 months (P > .05). Postoperative corrected distance visual acuity and residual manifest refractive spherical equivalent were similar between the groups (P > .05). The postoperative residual refractive astigmatism in the TCAT group was greater than that in the WFO group (P < .05). The optical path difference and root mean square of higher order aberrations and coma were significantly lower in eyes in the TCAT group at postoperative 1 and 6 months (P < .05).

CONCLUSIONS:

TCAT in virgin eyes induced less corneal optical path difference, fewer higher order aberrations, and less coma than WFO LASIK. However, TCAT was not as accurate as WFO, especially in astigmatism correction. A better compensation method for TCAT is warranted.

[J Refract Surg. 2019;35(9):575–582.]

Refractive laser surgery is becoming more popular because of its increasing efficacy and safety. The main complaints of patients after surgery are decreased visual sharpness and problems with night vision, such as glare, halo, and starbursts.1 The main causes of these problems are the increase of corneal asphericity and the introduction of higher order aberrations (HOAs) due to ablation algorithm, decentration, optical role of the flap, wound healing, biomechanical effects, reflection losses, and non-normal incidence of the laser on the cornea.2–6 To further improve the postoperative visual quality, various improved laser ablation algorithms have been developed.

Wavefront-optimized (WFO) ablation attempts to reduce the induction of spherical aberration by adding peripheral pulses, blending it with the central ablation profile and maintaining the prolate shape of the cornea.7 Wavefront-guided ablation uses aberrometers to measure HOAs, following which a customized ablation pattern is used to treat the total HOAs of the eye.8,9 Topography-guided customized ablation treatment (TCAT) attempts to maintain the aspheric shape of the cornea and neutralize corneal irregularities.10 TCAT has been shown to be effective in treating irregular astigmatism caused by iatrogenic corneal irregularities.11–13 Recent studies demonstrating outcomes of TCAT in normal corneas of virgin eyes have been promising.14–17 Meanwhile, several studies have compared the clinical outcomes following TCAT and WFO LASIK in virgin eyes, and found similar or slightly better outcomes for TCAT LASIK.18–22 However, these studies had a small sample size, and there are some contradictions in the results of different studies.

Based on this, we conducted this large-sample contralateral eye study to further explore the clinical differences between the two ablation methods. The aim of the study was to compare the effectiveness, safety, predictability, accuracy, and corneal optical quality between WFO and TCAT LASIK for the treatment of myopia and myopic astigmatism in the contralateral eyes.

Patients and Methods

Patients

Four hundred thirty-two eyes of 216 myopic patients who underwent femtosecond laser–assisted LASIK in both eyes at Peking University Third Hospital from May 2016 to July 2018 were enrolled in this prospective, randomized, contralateral interventional study. One eye of each patient was randomly assigned to the TCAT group and the fellow eye to the WFO group. The study received approval from the ethics committee of our institute and was conducted in accordance with the tenets of the Declaration of Helsinki. A written informed consent was obtained from each patient prior to the surgical procedure.

The inclusion criteria were age older than 18 years, spherical equivalent refraction of up to −10.00 diopters (D), with a documented refractive stability for a minimum period of 1 year and discontinuation of soft contact lenses for at least 2 weeks. Exclusion criteria included a residual stromal bed lower than 280 µm, topographic evidence of corneal ectasia, anisometropia of greater than 1.00 D, manifest astigmatism difference of greater than 0.75 D to the measured refraction calculated by the topography algorithm at “Measured,” previous ocular surgery, history of herpetic eye disease, corneal scarring, collagen vascular disease, pregnancy, and lactation.

Preoperative Examinations

Preoperative evaluation included uncorrected (UDVA) and corrected (CDVA) distance visual acuity, manifest refraction, slit-lamp biomicroscopy, dilated fundus evaluation, corneal thickness (A scan; Tomey Corporation, Nagoya, Japan), corneal tomography (Sirius; CSO, Florence, Italy), and corneal topography (Vario Topolyzer, WaveLight; Alcon Laboratories, Inc., Fort Worth, TX). The total corneal aberrations and optic quality in a 6-mm zone were obtained from corneal tomography. Parameters of corneal aberrations and optical quality included optical path difference; root mean square (RMS) of HOAs, corneal astigmatism, spherical aberration, and coma; and Strehl ratio. Corneal topography data for TCAT was obtained from the Vario Topolyzer Placido-based topography.

Surgical Procedures

All surgeries were performed by an experienced refractive surgeon (YC) under topical anesthesia. A table of random numbers was used to determine the eye to be treated with TCAT LASIK, whereas the fellow eye underwent WFO LASIK. All flaps were created by the WaveLight FS200 laser. The flap/canal/hinge parameters were: flap thickness of 110 µm; flap diameter of 8.5 to 9 mm; side-cut angle of 90°; hinge angle of 50°; and canal width of 1.5 mm. Following blunt dissection and flap lift, the stromal bed was ablated with an excimer laser (EX500 WaveLight) using an optic zone of 6 to 6.5 mm with a 1.25-mm transition zone. The refraction data (sphere, cylinder, and axis) used for the eyes randomized in the TCAT group followed the topography-modified refraction scheme introduced by Kanellopoulos.23 The refraction data used for the eyes randomized to the WFO group was the subjective manifest refraction. The ablation center was automatically adjusted to the corneal vertex in both groups.

Postoperative Care and Follow-up

Postoperatively, both eyes received treatment with 0.1% fluorometholone (FML; Allergan Pharmceuticals, Dublin, Ireland) in tapering dose for 4 weeks, 0.5% levofloxacin (Cravit; Santen Pharmaceutical (China) Co. Ltd., Jiangsu, China) four times a day for 2 weeks, and lubricating drops four times a day for 4 weeks. Follow-up visits included postoperative days 1 and 7 and months 1 and 6. The follow-up examinations involved measurements of UDVA, slit-lamp examination, subjective refraction, CDVA, and corneal tomography (Sirius).

Statistical Analysis

Data were analyzed using SPSS software (version 21.0; SPSS, Inc., Chicago, IL). The Kolmogorov–Smirnov test was used for confirming normality of data. The normally distributed data were represented as mean ± standard deviation and compared between the groups using the paired-sample t test. The non-normally distributed data were represented as median and analyzed using Wilcoxon signed-rank test. Comparison of the percentage of eyes between the groups used the Pearson chi-square test. A P value of less than .05 was considered statistically significant.

Results

This study included 148 women and 68 men. Mean age at the time of the operation was 28.0 ± 6.9 years (range: 18 to 47 years). There was no statistically significant difference between the two groups regarding preoperative visual acuity, refraction, corneal curvature, corneal aberrations, and Strehl ratio (P > .05) (Table 1).

Comparison of Preoperative Parameters

Table 1:

Comparison of Preoperative Parameters

UDVA outcome

At postoperative 1 month, median UDVA was −0.04 logMAR in the TCAT group and −0.08 logMAR in the WFO group, with a statistically significant difference between the groups (P = .001). UDVA of 20/20 or better was measured in 89.4% of eyes in the TCAT group and 93.5% of eyes in the WFO group (P = .021) (Figure 1A).

Uncorrected distance visual acuity (A) 1 month and (B) 6 months after surgery in the topography-guided customized ablation treatment (TCAT) group and wavefront-optimized (WFO) ablation group.

Figure 1.

Uncorrected distance visual acuity (A) 1 month and (B) 6 months after surgery in the topography-guided customized ablation treatment (TCAT) group and wavefront-optimized (WFO) ablation group.

At postoperative 6 months, median UDVA was −0.04 logMAR in both groups (P = .221). UDVA of 20/20 or better was measured in 89.6% of eyes in the TCAT group and 90.9% of eyes in the WFO group (P = .235) (Figure 1B).

CDVA Outcome and Safety

At postoperative 1 month, 12.5% of the eyes in the TCAT group versus 15.3% in the WFO group gained one line. A gain of two lines was noted in 5.1% and 3.7% of the eyes in the TCAT and WFO groups, respectively, and 5.5% of the eyes in both groups lost one line (P = .838) (Figure 2A).

Change in Snellen lines of corrected distance visual acuity (A) 1 month and (B) 6 months after surgery in the topography-guided customized ablation treatment (TCAT) group and wavefront-optimized (WFO) ablation group.

Figure 2.

Change in Snellen lines of corrected distance visual acuity (A) 1 month and (B) 6 months after surgery in the topography-guided customized ablation treatment (TCAT) group and wavefront-optimized (WFO) ablation group.

At postoperative 6 months, 19.5% of the eyes in the TCAT group versus 15.3% in the WFO group gained one line. A gain of two lines was noted in 6.5% and 3.7% of the eyes in the TCAT and WFO groups, respectively, and 2.6% of the eyes in the TCAT group versus 5.5% in the WFO group lost one line (P = .618) (Figure 2B).

Refractive Outcome

Figure 3 demonstrates the scatter plot analysis comparing attempted and achieved spherical equivalent correction in the TCAT and WFO groups at 1-month follow-up, respectively. The coefficient of determination between the attempted and achieved manifest refraction spherical equivalent (MRSE) was similar between the TCAT (R = 0.959) and WFO (R = 0.957) groups.

Attempted versus achieved spherical equivalent (SEQ) in the form of a scatter plot 1 month after surgery in the (A) topography-guided customized ablation treatment (TCAT) group and (B) wavefront-optimized (WFO) ablation group.

Figure 3.

Attempted versus achieved spherical equivalent (SEQ) in the form of a scatter plot 1 month after surgery in the (A) topography-guided customized ablation treatment (TCAT) group and (B) wavefront-optimized (WFO) ablation group.

At postoperative 1 and 6 months, there were statistically significant differences in refractive sphere, astigmatism, and MRSE between the two groups (P < .05) (Table 2). At postoperative 1 month, the residual MRSE within ±0.13 D was achieved by 39.8% of eyes in the TCAT group compared to 46.3% of eyes in the WFO group (P = .283) (Figure 4A). At postoperative 6 months, the residual MRSE within ±0.13 D was achieved by 59.7% of eyes in the TCAT group compared to 64.9% of eyes in the WFO group (P = .118) (Figure 4B).

Comparison of Refractive Outcomes 1 and 6 Months Postoperatively (Mean ± Standard Deviation)

Table 2:

Comparison of Refractive Outcomes 1 and 6 Months Postoperatively (Mean ± Standard Deviation)

Spherical equivalent refractive accuracy (A) 1 month and (B) 6 months after surgery in the topography-guided customized ablation treatment (TCAT) group and wavefront-optimized (WFO) ablation group.

Figure 4.

Spherical equivalent refractive accuracy (A) 1 month and (B) 6 months after surgery in the topography-guided customized ablation treatment (TCAT) group and wavefront-optimized (WFO) ablation group.

Postoperative refractive astigmatism is noted in Figure 5. At 1 month, 62.5% of eyes in the TCAT group and 70% of eyes in the WFO group were 0.25 D or less. The difference between groups was statistically significant (P = .04). At 6 months, 58.4% of eyes in the TCAT group and 76.6% of eyes in the WFO group were 0.25 D or less. The difference between groups was statistically significant (P = .02).

Refractive astigmatism accuracy (A) 1 month and (B) 6 months after surgery in the topography-guided customized ablation treatment (TCAT) group and wavefront-optimized (WFO) ablation group. D = diopters

Figure 5.

Refractive astigmatism accuracy (A) 1 month and (B) 6 months after surgery in the topography-guided customized ablation treatment (TCAT) group and wavefront-optimized (WFO) ablation group. D = diopters

Corneal Aberrations and Visual Quality

At postoperative 1 month, optical path difference and RMS of HOAs, astigmatism, and coma in the TCAT group were significantly lower than those in the WFO group (P < .05). Strehl ratio in the TCAT group was significantly greater than that in the WFO group (P < .001). At 6-month follow-up, only optical path difference and RMS of HOAs and coma in the TCAT group were still significantly lower than those in the WFO group (P < .05) (Table 3).

Comparison of Corneal Aberrations and Visual Quality at 1 and 6 Months Postoperatively

Table 3:

Comparison of Corneal Aberrations and Visual Quality at 1 and 6 Months Postoperatively

Discussion

The current study found that corneal optical path difference, HOAs, astigmatism, and coma were significantly lower, and Strehl ratio was significantly higher in the TCAT group at postoperative 1 month. These outcomes indicated that TCAT LASIK produced a more regular corneal surface and better corneal optical quality than WFO LASIK in the early postoperative period. As time went by, the advantage of TCAT slightly diminished and optical path difference, HOAs, and coma were still significantly lower than WFO at postoperative 6 months. To the best of our knowledge, no previous study compared postoperative 1-month outcomes between the TCAT and WFO profiles. Shetty et al.'s findings19 suggested that TCAT might perform slightly better than the WFO ablation profile in terms of induced spherical aberration and coma at postoperative 6 months. El Awady et al.18 also found TCAT induced fewer HOAs in vertical coma at 6 months. However, Tiwari et al.20 found that corneal HOAs induced were not significantly different between the TCAT eyes and the contralateral WFO eyes. Compared to these previous studies, the current study showed a more obvious aberration-reducing effect of TCAT, which might be due to the large sample in the current study and different measuring instruments for corneal aberrations. The effect of inducing fewer aberrations decreased slightly over time, possibly because the non-uniform remodeling of the corneal epithelium might weaken the effect of TCAT.24

Because TCAT for normalizing the anterior cornea could cause refractive change,25 the subjective manifest refraction should be adjusted to keep it neutral after refractive correction. Kanellopoulos23 and Wallerstein et al.26 found that topography-modified refraction offered superior refractive and visual outcomes to standard clinical refraction in myopic TCAT LASIK. Thus, in the current study, topography-modified refraction was applied to the TCAT design of cylinder and axis. The current study found that CDVA and MRSE predictability were similar between the groups, but UDVA was better and refraction was more accurate in the WFO group at postoperative 1 month. At 6 months, the visual and refractive outcomes in the TCAT group became better and both postoperative UDVA and CDVA were similar between the two groups. However, cylinder accuracy was still better in the WFO group. These findings showed that topography-modified refraction for TCAT was not accurate in our patients. Several previous studies found similar refractive and visual outcomes following TCAT and WFO LASIK,18–22 but the specific TCAT designs were not mentioned.18–21 Better compensation methods for TCAT are needed to obtain more accurate refractive results.

The limitations of this study are as follows. First, we only compared visual acuity, refraction, and corneal aberration between the two groups, and other parameters related to visual quality, such as discrimination indexes27 and contrast sensitivity function, were not studied. Second, algorithms are proprietary and we do not really know what platforms (TCAT or WFO) do during ablation. So the fundamental analysis of the two types of ablation are scarce.

TCAT LASIK in normal corneas could induce fewer corneal HOAs and less optical path difference than WFO LASIK at postoperative 6 months. However, topography-modified refraction for TCAT was not as accurate as for WFO, especially in astigmatism correction. Further understanding of the ablation algorithms and more research is needed to find a more accurate design method for TCAT to further improve postoperative visual acuity and refractive outcomes.

References

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Comparison of Preoperative Parameters

ParameterTCAT Group (n = 216)WFO Group (n = 216)P
UDVA (logMAR), median1.11.1.482
CDVA (logMAR), median−0.04−0.04.627
Sphere (D), mean ± SD−5.61 ± 1.56−5.57 ± 1.61.578
Cylinder (D), mean ± SD−1.11 ± 0.77−1.03 ± 0.76.149
MRSE (D), mean ± SD−6.17 ± 1.62−6.09 ± 1.68.264
Flat K (D), mean ± SD42.13 ± 1.5842.16 ± 1.64.358
Steep K (D), mean ± SD43.25 ± 1.6743.21 ± 1.52.521
OPD (µm), median1.081.04.341
RMSh (µm), median0.380.38.848
AST RMS (µm), median1.020.97.305
Coma RMS (µm), median0.200.20.452
SA RMS (µm), mean ± SD0.20 ± 0.070.20 ± 0.08.490
SR, median0.110.12.119

Comparison of Refractive Outcomes 1 and 6 Months Postoperatively (Mean ± Standard Deviation)

Parameter1 Month6 Months


TCAT GroupWFO GroupPTCAT GroupWFO GroupP
Sphere (D)0.27 ± 0.370.10 ± 0.35< .0010.11 ± 0.23−0.04 ± 0.27< .001
Cylinder (D)−0.29 ± 0.31−0.22 ± 0.27.011−0.29 ± 0.26−0.20 ± 0.21.016
MRSE (D)0.13 ± 0.35−0.01 ± 0.35< .001−0.04 ± 0.23−0.14 ± 0.26< .001

Comparison of Corneal Aberrations and Visual Quality at 1 and 6 Months Postoperatively

Parameter1 Montha6 Monthsb


TCAT GroupWFO GroupPTCAT GroupWFO GroupP
OPD (µm)0.710.93< .0010.87 ± 0.350.96 ± 0.27.003
RMSh (µm)0.620.70.0020.660.78.046
AST RMS (µm)0.300.49< .0010.330.41.060
Coma RMS (µm)0.320.37< .0010.38 ± 0.240.45 ± 0.25.015
SA RMS (µm)0.400.45.0610.440.47.989
SR0.180.15< .0010.18 ± 0.050.16 ± 0.05.081
Authors

From the Department of Ophthalmology, Peking University Third Hospital, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Beijing, China.

Supported by Capital's Funds for Health Improvement and Research (Grant No. 2018-2-4092).

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (YC); data collection (YZ, YC); analysis and interpretation of data (YZ); writing the manuscript (YZ); critical revision of the manuscript (YC)

Correspondence: Yueguo Chen, MD, 49 North Huayuan Road, Haidian District, Beijing 100191, China. E-mail: chenyueguo@263.net

Received: May 16, 2019
Accepted: August 19, 2019

10.3928/1081597X-20190819-01

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