Journal of Refractive Surgery

Original Article Supplemental Data

A Prospective Study to Compare Visual Outcomes Between Wavefront-optimized and Topography-guided Ablation Profiles in Contralateral Eyes With Myopia

Rohit Shetty, MD, FRCS, PhD; Rushad Shroff, MD; Kalyani Deshpande, MD; Roshan Gowda, MD; Sumeet Lahane, MD; Chaitra Jayadev, MD

Abstract

PURPOSE:

To analyze refractive outcomes of wavefront-optimized (WFO) ablation and topography-guided custom ablation (TCAT) profiles using the Allegretto Wave excimer laser platform (Alcon Laboratories, Inc., Fort Worth, TX) in the treatment of myopia.

METHODS:

Sixty eyes of 30 patients who underwent LASIK were included in this prospective interventional study. WFO ablation was performed in one eye (WFO group) and TCAT in the fellow eye (TCAT group). The WaveLight FS200 femtosecond laser (Alcon Laboratories, Inc.) was used to create the flap and Allegretto Wave excimer laser (Alcon Laboratories, Inc.) was used for photoablation. The Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) and Allegretto Topolyzer (Alcon Laboratories, Inc.) were used to measure the corneal aberrations. Refractive visual outcomes were also compared.

RESULTS:

Accuracy, safety, and efficacy were similar in the two groups. The total root mean square (RMS) and RMS of lower order aberrations were significantly better in eyes that underwent TCAT (P < .05). There was a decrease in individual higher order aberrations in the TCAT group, with a statistically significant difference in the spherical aberrations (P = .02). The corneal asphericity (Q value) was not significantly different between the WFO (0.6 ± 0.1) and TCAT (0.51 ± 0.09) groups. The postoperative total RMS of higher order aberrations was lower in the TCAT group, but this was not statistically significant (P > .05). There was a more positive change in Q value and spherical aberrations in the WFO group, but this was not statistically significant.

CONCLUSIONS:

TCAT and WFO ablation provided essentially equivalent outcomes after myopic LASIK, with induction of fewer lower order aberrations and higher order aberrations following TCAT ablation.

[J Refract Surg. 2017;33(1):6–10.]

Abstract

PURPOSE:

To analyze refractive outcomes of wavefront-optimized (WFO) ablation and topography-guided custom ablation (TCAT) profiles using the Allegretto Wave excimer laser platform (Alcon Laboratories, Inc., Fort Worth, TX) in the treatment of myopia.

METHODS:

Sixty eyes of 30 patients who underwent LASIK were included in this prospective interventional study. WFO ablation was performed in one eye (WFO group) and TCAT in the fellow eye (TCAT group). The WaveLight FS200 femtosecond laser (Alcon Laboratories, Inc.) was used to create the flap and Allegretto Wave excimer laser (Alcon Laboratories, Inc.) was used for photoablation. The Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) and Allegretto Topolyzer (Alcon Laboratories, Inc.) were used to measure the corneal aberrations. Refractive visual outcomes were also compared.

RESULTS:

Accuracy, safety, and efficacy were similar in the two groups. The total root mean square (RMS) and RMS of lower order aberrations were significantly better in eyes that underwent TCAT (P < .05). There was a decrease in individual higher order aberrations in the TCAT group, with a statistically significant difference in the spherical aberrations (P = .02). The corneal asphericity (Q value) was not significantly different between the WFO (0.6 ± 0.1) and TCAT (0.51 ± 0.09) groups. The postoperative total RMS of higher order aberrations was lower in the TCAT group, but this was not statistically significant (P > .05). There was a more positive change in Q value and spherical aberrations in the WFO group, but this was not statistically significant.

CONCLUSIONS:

TCAT and WFO ablation provided essentially equivalent outcomes after myopic LASIK, with induction of fewer lower order aberrations and higher order aberrations following TCAT ablation.

[J Refract Surg. 2017;33(1):6–10.]

In an attempt to enhance functional outcomes and reduce spherical aberration after surgery, various ablation profiles have been designed. Wavefront-optimized (WFO) ablation uses a precalculated spherical aberration treatment to create an aspherical ablation profile.1,2 Wavefront-guided ablation uses aberrometers to measure higher order aberrations (HOAs), following which a customized ablation pattern is used to treat the total HOAs of the eye.3 Topography-guided custom ablation (TCAT) attempts to maintain the aspheric shape of the cornea and neutralize corneal irregularities. TCAT has been shown to be effective in highly aberrated and irregular corneas where aberrometry is not reliable.4 Studies have shown that this method is safe and effective in the management of irregular corneal astigmatism and myopia secondary to previous corneal surgeries or disease.4,5 However, outcomes in terms of aberrations, changes in asphericity, and refractive results have not been reported in detail.6

The relative lack of contralateral studies that have compared WFO ablation and TCAT treatments and the need for refined refractive outcome measures and aberration data analysis prompted this study. The aim of the study was to compare the refractive outcomes of WFO ablation and TCAT using the Allegretto Wave excimer laser platform (EX500 WaveLight; Alcon Laboratories, Inc., Fort Worth, TX) in the treatment of myopic patients with and without astigmatism.7

Patients and Methods

Sixty eyes of 30 consecutive patients (14 male and 16 female) undergoing femtosecond laser-assisted LASIK were included in this prospective, interventional study. The study was conducted in accordance with the tenets of the Declaration of Helsinki and was approved by the institutional research and ethics committee of Narayana Nethralaya Eye Hospital. A written informed consent was obtained from all patients before the procedure.

Study Population

Patients between 18 and 50 years of age with stable myopia for a minimum period of 1 year (a change of 0.25 diopters [D] or less), a corrected distance visual acuity (CDVA) of 20/25 or better, a spherical equivalent refraction less than 10.00 D, and a refractive astigmatism less than 3.00 D were included in the study. Exclusion criteria included a central corneal thickness less than 480 µm, a calculated residual stromal bed thickness of less than 250 µm after the surgery, patients with a history of keratoconus, diabetes, collagen vascular disease, pregnancy, breastfeeding, and any prior ocular surgery. Patients with an anisometropia of more than 1.00 D of spherical or 0.50 D of cylindrical refractive error were excluded.

Study Design

Eligible patients underwent a detailed ocular examination, which included visual acuity and manifest refraction assessment and funduscopy. Aberration measurements and corneal topography were performed using the Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany). Corneal topography data for TCAT and Q value (asphericity) calculation were obtained from the Placido-based Allegretto Topolyzer (version 1.59; Alcon Laboratories, Inc.) prior to and 6 months after LASIK. The Q value was calculated in the four main hemi-meridians at radial distances of 10°, 15°, 20°, 25°, and 30° from the corneal apex. An average of two opposite hemi-meridians was used as the Q value in the main axes for treatment. Preoperative and postoperative Q values were obtained as averages of all four hemi-meridians. Postoperative target Q value was −0.4 to obtain a prolate cornea.8,9

Study Treatments and Procedures

All surgeries were performed by a single experienced surgeon (RShetty) under aseptic precautions and topical anesthesia after instilling 0.5% proparacaine hydrochloride (Paracain; Sunways Pvt. Ltd., Mumbai, India). One eye of each patient was randomly assigned to the WFO group and the fellow eye to the TCAT group. Topography-guided treatment was planned for both eyes prior to surgery and during the surgery one eye was selected for TCAT using a random digit table. The other eye was treated using the WFO ablation profile.

The WaveLight FS200 femtosecond laser (Alcon Laboratories, Inc.) was used to create a flap thickness of 110 µm and a flap diameter of 9 mm with a 70° angled side cut. The optical diameter was 6 mm. Spot and line separations were 8 and 8 µm for the bed cut and 5 and 3 µm for the side cut, respectively. The hinge was placed superiorly at an angle of 55°. After drying the stromal bed, excimer laser ablation was performed (EX500 WaveLight). The bed was thoroughly irrigated with saline and the flap repositioned on the stromal bed. In both groups, a tapering dose of topical prednisolone acetate 1% (Allergan Inc., Irvine, CA) three times a day for 3 days, two times a day for the next 3 days, and once a day for the last 2 days was administered after surgery. A topical antibiotic drop (Vigamox; Alcon Laboratories, Inc.) was administered four times a day for 1 week. Lubricating eye drops (Systane; Alcon Laboratories, Inc.) were administered six to eight times a day for 3 months.

Statistical Analysis

The Kolmogorov–Smirnov test was used for confirming normality of data. Because the data were normally distributed, parametric tests were employed and all continuous variables were represented as mean ± standard deviation. The Student's t test was used to compare the uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), spherical and cylindrical error, mean refractive spherical equivalent (MRSE), and aberrations with the Pentacam before and after the surgical procedure for each eye and between the surgical groups. Zernike coefficients were analyzed in a 6-mm zone with a maximum order limited to 8. A two-sided P value of less than .05 was considered statistically significant. Univariate regression was used to assess the change in Q value and spherical aberration with change in the refractive spherical equivalent. All statistical analyses were performed using MedCalc software (version 15.6.1; MedCalc Inc., Ostend, Belgium).

Results

The mean age of the patients was 27.2 ± 5.6 years (range: 18 to 35 years). The preoperative CDVA, UDVA, spherical and cylindrical refractive error, and MRSE were similar in both groups (Table 1). Six months following the procedure, there was no significant difference in the parameters mentioned above between the two groups. In the WFO group, 93% of eyes achieved a UDVA of 20/20 or better at 6 months. These percentages were not significantly different in the TCAT group (97%, P = .61). The CDVA remained stable in 83.3% and 90% of the eyes in the WFO and TCAT groups, respectively (P = .70, Figure 1). Figure 2 demonstrates that the percentage of eyes with a spherical equivalent less than +0.50 D was 80% in the WFO group and 83% in the TCAT group (P = .90). The coefficient of determination between the attempted and achieved MRSE was also similar (P = .89) between the WFO (R2 = 0.96) and TCAT (R2 = 0.97) groups.


Mean ± SD of Preoperative Parameters for WFO and TCAT Profiles

Table 1:

Mean ± SD of Preoperative Parameters for WFO and TCAT Profiles


Standard refractive graphs showing refractive outcomes 6 months after surgery in the wavefront-optimized (WFO) ablation and topography-guided custom ablation (TCAT) groups. Percentage of eyes that achieved uncorrected visual acuity of 20/20 in the (A) TCAT and (B) WFO groups. The number of lines lost and gained in the (C) TCAT and (D) WFO groups. CDVA = corrected distance visual acuity; UDVA = uncorrected distance visual acuity

Figure 1.

Standard refractive graphs showing refractive outcomes 6 months after surgery in the wavefront-optimized (WFO) ablation and topography-guided custom ablation (TCAT) groups. Percentage of eyes that achieved uncorrected visual acuity of 20/20 in the (A) TCAT and (B) WFO groups. The number of lines lost and gained in the (C) TCAT and (D) WFO groups. CDVA = corrected distance visual acuity; UDVA = uncorrected distance visual acuity


Standard refractive graphs showing refractive outcomes 6 months after surgery in the wavefront-optimized (WFO) ablation and topography-guided custom ablation (TCAT) groups. Attempted versus achieved spherical equivalent (SEQ) in the form of a scatter plot in the (A) TCAT and (B) WFO groups. Spherical equivalent refractive accuracy in terms of number of eyes that were within ±0.50 diopters (D) of the attempted correction in the (C) TCAT and (D) WFO groups.

Figure 2.

Standard refractive graphs showing refractive outcomes 6 months after surgery in the wavefront-optimized (WFO) ablation and topography-guided custom ablation (TCAT) groups. Attempted versus achieved spherical equivalent (SEQ) in the form of a scatter plot in the (A) TCAT and (B) WFO groups. Spherical equivalent refractive accuracy in terms of number of eyes that were within ±0.50 diopters (D) of the attempted correction in the (C) TCAT and (D) WFO groups.

As shown in Table A (available in the online version of this article), the total RMS of the anterior surface of the cornea was higher (P = .04) in the WFO group (2.04 ± 0.72) than in the TCAT group (1.73 ± 0.61) 6 months after surgery. The total RMS of the entire cornea was also higher (P = .04) in the WFO group (1.94 ± 0.78) than the TCAT group (1.60 ± 0.63). The RMS of lower order aberrations for the anterior surface (P = .04) and entire cornea (P = .03) was significantly greater in the WFO group.


Mean ± SD of Wavefront Aberrations in the WFO and TCAT Profiles

Table A:

Mean ± SD of Wavefront Aberrations in the WFO and TCAT Profiles

Six months after the procedure, the Q value was +0.60 in the WFO group and +0.51 in the TCAT group. The induced positive spherical aberration 6 months after the surgery was 0.42 ± 0.25 in the TCAT group and 0.57 ± 0.25 in the WFO group.

Regression analysis was used to study the change in Q value and spherical aberration for each diopter of myopic treatment in the WFO and TCAT groups. For each diopter of myopic treatment, there was a +0.20 increase in the Q value in the WFO group and a +0.17 increase in the TCAT group. Spherical aberration changed by 0.08 in the WFO group and 0.07 in the TCAT group for each diopter of myopic correction.

Discussion

The current study demonstrates that the percentage of patients with a UDVA of 20/20 or better was similar in the two groups. The refractive outcomes in terms of safety, accuracy, and efficacy were also statistically similar in the two groups following refractive surgery. Farooqui and Al-Muammar6 reported similar visual outcomes in a contralateral study comparing TCAT and conventional LASIK using the NIDEK EC-5000 Advanced Vision Excimer laser system.

Aberrations induced by refractive surgery have been correlated with halos, glare, and poor optical performance. Several studies have shown a significant increase in corneal and total aberrations after laser refractive correction.10,11 It is therefore imperative to understand and quantify aberrations induced by laser refractive surgery to formulate algorithms for customization of ablation profiles to improve outcomes.12 On studying aberrations, we found that the anterior surface and total RMS values were lower but not significantly different in eyes that were treated using the TCAT profile. The total RMS of higher order aberrations was lower in eyes that had undergone TCAT, but this was not statistically significant. To the best of our knowledge, this has not been demonstrated before in a contralateral eye study comparing WFO and TCAT ablation profiles. Furthermore, there was a difference in the value of induced spherical aberration and coma in the two groups. Farooqui and Al-Muammar showed lower values of induced spherical aberration and coma in eyes that underwent TCAT in their study comparing TCAT with conventional LASIK.6 WFO ablation has been reported to maintain corneal asphericity and induce fewer aberrations than conventional LASIK.2 Although we did not analyze conventional LASIK in this study, our findings suggest that TCAT may perform slightly better than the aspheric WFO ablation profile in terms of induced spherical aberration and coma.

We found a positive change in Q value in both groups, with a greater positive change in eyes that were treated using the WFO ablation profile. However, this difference was not statistically significant. The amount of change in Q value with each diopter of myopia treated was also greater but not significantly different in eyes that underwent WFO treatment.

In the current study, we compared multiple aberrations between the two groups. The large number of comparisons may have increased the chance of a type I error during hypothesis testing. Several methods have been proposed to potentially correct for multiple comparisons in the statistics literature, but there is no consensus on whether they should be routinely applied and what specific method should be employed.12–14 When we applied Bonferroni correction and reduced the type I error rate to 0.005, many of the differences between the groups lost statistical significance. It is important to emphasize that some of the differences detected in our study could also be specific to the sample used in our study. Therefore, investigations using different populations should be performed to further evaluate and validate differences in outcomes as detected in our study.

Refractive outcome in terms of lines lost or gained, spherical equivalent achieved, and percentage of eyes that obtained 20/20 vision was similar in both the WFO and TCAT groups. The current study also found less change in corneal asphericity and lower RMS values of lower order and higher order aberrations such as coma and spherical aberrations in eyes treated with TCAT. These findings suggest that although both WFO and topography-guided regimens are equally accurate, safe, and effective in correcting myopia and myopic astigmatism, TCAT may have a lesser effect on the corneal shape and aberrations.

References

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Mean ± SD of Preoperative Parameters for WFO and TCAT Profiles

ParameterBefore Surgery6 Months After Surgery


WFO (n = 30)TCAT (n = 30)PaWFO (n = 30)TCAT (n = 30)Pa
Sphere (D)−4.55 ± 2.39−4.39 ± 2.37.78−0.24 ± 0.56−0.16 ± 0.51.52
Cylinder (D)−1.10 ± 0.76−1.08 ± 0.71.93−0.53 ± 0.27−0.51 ± 0.23.77
MRSE (D)−5.08 ± 2.50−4.93 ± 2.47.78−0.50 ± 0.53−0.41 ± 0.49.45
CDVA (logMAR)0.019 ± 0.070.002 ± 0.04.219−0.01 ± 0.05−0.01 ± 0.04.78
UDVA (logMAR)1.28 ± 0.351.25 ± 0.34.662−0.00 ± 0.05−0.01 ± 0.043.33

Mean ± SD of Wavefront Aberrations in the WFO and TCAT Profiles

ParameterBefore Surgery6 Months After Surgery


WFO (n = 30)TCAT (n = 30)PaWFO (n = 30)TCAT (n = 30)Pa
Front WFA RMS total1.77 ± 0.501.75 ± 0.50.862.04 ± 0.721.73 ± 0.61.049b
Front WFA RMS LOA1.74 ± 0.531.73 ± 0.55.931.86 ± 0.681.55 ± 0.58.035b
Front WFA RMS HOA0.36 ± 0.070.37 ± 0.08.680.81 ± 0.300.7571 ± 0.30.39
Front WFA N2 astigmatism 45−0.04 ± 0.550.32 ± 0.37.0015b−0.074 ± 0.32.03 ± 0.28.15
Front WFA N2 defocus0.88 ± 0.270.82 ± 0.29.420.89 ± 0.590.71 ± 0.56.17
Front WFA N2 astigmatism 0−0.92 ± 0.90−0.87 ± 0.95.80−0.61 ± 0.44−0.65 ± 0.40.66
Front WFA N3 coma 90−0.08 ± 0.16−0.08 ± 0.18.85−0.23 ± 0.38−0.10 ± 0.36.15
Front WFA N3 coma 00.02 ± 0.140.12 ± 0.11.002−0.036 ± 0.260.12 ± 0.21.01b
Total WFA RMS total1.53 ± 0.531.46 ± 0.55.581.94 ± 0.781.60 ± 0.63.041b
Total WFA RMS LOA1.47 ± 0.511.42 ± 0.54.641.73 ± 0.751.38 ± 0.59.03b
Total WFA RMS HOA0.36 ± 0.080.36 ± 0.08.890.85 ± 0.330.78 ± 0.33.37
Total WFA N2 astigmatism 45−0.03 ± 0.510.30 ± 0.35.002b−6.78 ± 5.200.007 ± 0.27.48
Total WFA N2 defocus0.55 ± 0.300.46 ± 0.31.180.57 ± 0.620.37 ± 0.63.14
Total WFA N2 astigmatism 0−0.81 ± 0.86−0.75 ± 0.90.78−0.39 ± 0.46−0.41 ± 0.42.81
Total WFA N3 coma 90−0.09 ± 0.16−0.09 ± 0.16.95−0.24 ± 0.42−0.14 ± 0.37.28
Total WFA N3 coma 00.01 ± 0.140.087 ± 0.12.01b−5.69 ± 4.340.11 ± 0.23.47
Front WFA SA0.24 ± 0.060.23 ± 0.06.960.58 ± 0.230.44 ± 0.21.02b
TOTAL WFA SA0.20 ± 0.080.19 ± 0.10.870.57 ± 0.250.42 ± 0.21.02b
Q value−0.34 ± 0.12−0.35 ± 0.13.800.60 ± 0.500.51 ± 0.40.50
Authors

From the Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India.

Dr. Shetty has received research funding from Allergan Inc., Irvine, California, and Carl Zeiss Meditec, Oberkochen, Germany. The remaining authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (RShetty, RShroff, RG, SL, CJ); data collection (RShetty, RShroff, KD, RG, SL); analysis and interpretation of data (RShetty, RShroff, KD); writing the manuscript (RShetty, RShroff, KD, RG, SL, CJ); critical revision of the manuscript (RShetty, KD, RG, SL, CJ); statistical expertise (RShetty, RShroff, KD, RG, SL, CJ); administrative, technical, or material support (RShetty); supervision (RShetty, KD, RG, SL, CJ)

Correspondence: Rushad Shroff, MD, Narayana Nethralaya, 121/C, West of Chord Road, Rajaji Nagar, 1st ‘R’ Block, Bangalore, Karnataka 560010, India. E-mail: rushad09@gmail.com

Received: June 13, 2016
Accepted: September 01, 2016

10.3928/1081597X-20161006-01

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