Journal of Refractive Surgery

Original Article Supplemental Data

Effect of Cyclotorsion Compensation With a Novel Technique in Small Incision Lenticule Extraction Surgery for the Correction of Myopic Astigmatism

Jiping Xu, MD; Fang Liu, MD; Manli Liu, MD, PhD; Xiaonan Yang, MD, PhD; Shengbei Weng, MD; Limian Lin, MD; Haiqin Lin, MD; Yi Xie, MD; Quan Liu, MD, PhD

Abstract

PURPOSE:

To comparatively investigate the clinical outcomes of small incision lenticule extraction (SMILE) surgery with or without cyclotorsion compensation for the correction of myopic astigmatism.

METHODS:

This prospective, double-blinded, randomized controlled trial included patients who underwent SMILE surgery with bilateral myopic astigmatism. Two eyes of a single patient were randomly divided into the static cyclotorsion compensation (SCC) group and the control group. In the SCC group, the intraoperative cyclotorsion was manually compensated with a novel technique. In the control group, the cyclotorsion was not compensated. Visual acuity, manifest refraction, aberrations, objective visual quality, and contrast sensitivity were measured preoperatively and postoperatively.

RESULTS:

A total of 132 eyes from 66 patients were analyzed at the 3-month follow-up. The mean preoperative cylinder values in the SCC and control groups were −1.52 ± 0.81 and −1.57 ± 0.82 diopters (D), respectively. The mean cyclotorsion during surgery was 0.60° ± 0.63° (range: 0° to 3.2°) in the SCC group and 3.21° ± 2.33° (range: 0.1° to 10.8°) in the control group (P < .001). Both groups showed favorable results in the correction of myopic astigmatism. No statistically significant difference was found between the two groups in visual and refractive outcomes, vector parameters, entire eye aberrations, objective visual quality, or contrast sensitivity. No significant benefit was gained from cyclotorsion compensation, even in the high astigmatism subgroup.

CONCLUSIONS:

The cyclotorsion compensation technique used in this study helped minimize the alignment error but was not compulsory because the ocular rotation in SMILE surgery using a well-controlled position was too small to affect the astigmatic outcomes or postoperative visual quality.

[J Refract Surg. 2019;35(5):301–308.]

Abstract

PURPOSE:

To comparatively investigate the clinical outcomes of small incision lenticule extraction (SMILE) surgery with or without cyclotorsion compensation for the correction of myopic astigmatism.

METHODS:

This prospective, double-blinded, randomized controlled trial included patients who underwent SMILE surgery with bilateral myopic astigmatism. Two eyes of a single patient were randomly divided into the static cyclotorsion compensation (SCC) group and the control group. In the SCC group, the intraoperative cyclotorsion was manually compensated with a novel technique. In the control group, the cyclotorsion was not compensated. Visual acuity, manifest refraction, aberrations, objective visual quality, and contrast sensitivity were measured preoperatively and postoperatively.

RESULTS:

A total of 132 eyes from 66 patients were analyzed at the 3-month follow-up. The mean preoperative cylinder values in the SCC and control groups were −1.52 ± 0.81 and −1.57 ± 0.82 diopters (D), respectively. The mean cyclotorsion during surgery was 0.60° ± 0.63° (range: 0° to 3.2°) in the SCC group and 3.21° ± 2.33° (range: 0.1° to 10.8°) in the control group (P < .001). Both groups showed favorable results in the correction of myopic astigmatism. No statistically significant difference was found between the two groups in visual and refractive outcomes, vector parameters, entire eye aberrations, objective visual quality, or contrast sensitivity. No significant benefit was gained from cyclotorsion compensation, even in the high astigmatism subgroup.

CONCLUSIONS:

The cyclotorsion compensation technique used in this study helped minimize the alignment error but was not compulsory because the ocular rotation in SMILE surgery using a well-controlled position was too small to affect the astigmatic outcomes or postoperative visual quality.

[J Refract Surg. 2019;35(5):301–308.]

Small incision lenticule extraction (SMILE) is a femtosecond laser–assisted and flap-free refractive surgery technique that has shown high efficacy, safety, predictability, and stability in the correction of myopia with or without astigmatism.1–3 However, it has a tendency toward astigmatic under-correction, especially for the treatment of high astigmatism, and counterclockwise rotation of the cylindrical axis.4–7 The lenticule for astigmatic correction has an oval posterior surface with a steep and flat axis instead of a concentric one.2 Hence, rotation of this oval lenticule could potentially result in undesired astigmatic outcomes. Cyclotorsion of the eye from the upright to supine position and cursory alignment of the head or body, monocular fixation, the force from eye speculum, and the docking procedure may be the common factors that cause axial misalignment when correcting astigmatism in SMILE.8–10

Compared with excimer laser–based procedures that have active eye tracking systems, SMILE results in a larger angle of error and less favorable astigmatic correction outcomes.11–15 Previous studies suggest that even several degrees of rotational error may theoretically lead to significant undercorrection of astigmatism in refractive surgeries.16,17 Hence, most authors suggest that uncompensated cyclotorsion error due to the lack of active rotational tracking software in the VisuMax femtosecond laser system (Carl Zeiss Meditec, Jena, Germany) is a possible explanation for these results. However, the exact effect of this cyclotorsion error in SMILE on the accuracy of astigmatic correction remains unknown.

Cyclotorsion compensation assisted by manual limbal marking under the slit lamp has been widely used in cataract and refractive surgeries to improve the axial accuracy of astigmatic correction.16,18–21 This technique is commonly performed in SMILE surgery, especially when the target induced astigmatism is greater than 0.75 diopters (D).15,22 However, it is reported that this conventional manual limbal marking procedure still leaves a mean absolute error of 2.8° and could internally cause variance, with a range from 3.8° to 6°.20,21 This magnitude of personal error is prominent because the mean cyclotorsion in SMILE is reported to be only 5.65°.23 Static cyclotorsion compensation (SCC) of the AMARIS system (SCHWIND eye-tech-solutions, Kleinostheim, Germany) is an automated eye tracking technology that has shown improved accuracy of astigmatic correction in femtosecond laser–assisted laser in situ keratomileusis surgery.10,24 This system can compare both the iris and the scleral features from the upright to supine position with a mean repeatability value of 0.5° ± 0.5° (range: 0.1° to 1.3°).25 Thus, if we combine this technique with limbal marking, the personal error of cyclotorsion compensation in SMILE could be reduced to the minimum.

To our knowledge, no randomized controlled clinical studies have been performed to demonstrate the effect of cyclotorsion compensation on astigmatic outcomes in SMILE. The current study investigated the additional benefits obtained from cyclotorsion compensation in SMILE for astigmatic correction, using a novel technique that combines the SCC of the AMARIS system with manual limbal marking. To further study the impact of cyclotorsion on visual quality after surgery, entire eye aberrations, objective visual quality, and contrast sensitivity were also observed.

Patients and Methods

Patients

This prospective, double-blinded, randomized controlled clinical study was approved by the Ethics Committee of Zhongshan Ophthalmic Center of Sun Yat-sen University, and complied with the tenets of the Declaration of Helsinki. An informed consent was signed by all patients before the surgery. This research was registered in the Chinese Clinical Trial Registry (registration ID: ChiCTR1800014796).

This was a contralateral eye study, so cases included were those that had bilateral myopic astigmatism and underwent SMILE surgery for both eyes. Other inclusion criteria were age between 18 and 40 years, change of myopic diopter less than 1.00 D for the past 2 years, corrected distance visual acuity (CDVA) of 20/25 or better, thickness of the residual cornea matrix bed greater than 270 um in prediction, normal morphology in corneal topography, and no keratoconus. Exclusion criteria were other ocular abnormity or systemic diseases that may affect the recovery of surgery.

One eye from each patient was assigned to the SCC group and one eye to the control group using the random number table method. All cases were subcategorized for further analysis depending on the preoperative cylindrical power (low astigmatism group = −0.25 to −1.00 D, moderate astigmatism group = −1.25 to −2.00 D, high astigmatism group = < −2.00 D).

Surgical Techniques

Anterior segment parameters of all patients were obtained from the Sirius tomographer and corneal topographer (software version 2.6.3; SCHWIND eye-tech-solutions) in an upright position, including important landmarks such as rainbow shape of the iris and scleral vessels. Then the diagnosis image and parameters were transferred to the AMARIS excimer laser platform. After adequate anesthesia for the ocular surface and disinfection of the periocular skin, the patient was positioned supinely on the AMARIS platform. An eye speculum was placed and the patient was instructed to look at the green flashing fixation light. The eye tracker image would be obtained again under the AMARIS system and compared to the anterior images taken in the upright position. The difference of alignment between these two images was considered as the static cyclotorsion. If the value of static cyclotorsion was −1° or less or 1° or greater, the head and body of the patient were moved counterclockwise or clockwise. Then a new measurement was taken until the absolute value of static cyclotorsion was less than 1°. In this final position, two tiny points were marked on the limbus extending 1.5 to 2 mm toward the center of the cornea, along the horizontal projection line of the AMARIS platform (Figure AA, available in the online version of this article) using a skin marker pen (GRI-Alleset, Floerty Branch, GA, or Med-Plus Inc., Edison, NJ).

(A) Two tiny points were marked on the limbus extending 1.5 mm toward the center of the cornea, along the horizontal projection line of the AMARIS platform (SCHWIND eye-tech-solutions, Kleinostheim, Germany), using a skin marker pen. (B) For some eyes in the static cyclotorsion compensation (SCC) group, the cone was gently rotated until the horizontal marks were parallel with the 0° to 180° axis of the reticule. (C) VisuMax (Carl Zeiss Meditec, Jena, Germany) screenshots of an eye in the SCC group. The two red dots represent the position of corneal markers before rotation of the cone and the two blue dots are corneal markers after rotation. The dotted arrows represent the trajectory of rotation. (D) VisuMax screenshots of an eye in the control group without any compensation.

Figure A.

(A) Two tiny points were marked on the limbus extending 1.5 mm toward the center of the cornea, along the horizontal projection line of the AMARIS platform (SCHWIND eye-tech-solutions, Kleinostheim, Germany), using a skin marker pen. (B) For some eyes in the static cyclotorsion compensation (SCC) group, the cone was gently rotated until the horizontal marks were parallel with the 0° to 180° axis of the reticule. (C) VisuMax (Carl Zeiss Meditec, Jena, Germany) screenshots of an eye in the SCC group. The two red dots represent the position of corneal markers before rotation of the cone and the two blue dots are corneal markers after rotation. The dotted arrows represent the trajectory of rotation. (D) VisuMax screenshots of an eye in the control group without any compensation.

The patient was moved to the operative bed of the 500-kHz VisuMax femtosecond laser platform (Carl Zeiss Meditec, Jena, Germany). To avoid the alignment of the SCC eye affecting the ocular rotation error of the control eye, the surgery was performed first on the control eye, then on the SCC eye. The patient's head position was carefully checked without a microscope to avoid potential cyclotorsion caused by head rotation. After that, the surgeon was not allowed to adjust the head position again according to the limbal markings on the control eye under the eyepiece. There was no cyclotorsion compensation for the eyes in the control group (Figure AD). When operating on the eyes in the SCC group, the head position could be adjusted again according to the limbal markings under the eyepiece. After suction was on, if there was any cyclotorsion determined by the corneal mark points unaligned with the eyepiece reticule, the cone was gently rotated until the horizontal marks paralleled with the 0° to 180° axis of the reticule (Figures AB–AC). Other procedures and parameters were the same between the eyes in the two groups.

All operations were performed by a single experienced surgeon (QL). In both groups, the sphere was overcorrected approximately 10% according to our experience to achieve emmetropia. The parameters used for all cases were as follows: cut energy of 110 to 120 nJ with a spot distance of 4.5 µm, optical zone of 5.8 to 7.2 mm with a transition zone of 0.1 mm, cap thickness of 110 to 120 µm with a diameter of 7.4 to 7.6 mm, and incision width of 2 mm with a position at 130°.

Preoperative and Postoperative Evaluations

All patients had a detailed ophthalmic assessment before surgery to rule out the contraindications for SMILE. They were asked to follow up at 1 day, 1 week, 1 month, and 3 months after the operation. Uncorrected distance visual acuity (UDVA), manifest refraction through a phoropter using the cross-cylinder technique for cylinder refinement, CDVA, aberrometry (iTrace; Tracey Technologies, Houston, TX), objective visual quality (OQAS; Visiometrics SL, Barcelona, Spain), and contrast sensitivity (CSV-1000; Vector Vision, Greenville, OH) were assessed preoperatively and 3 months postoperatively.

The final ocular rotation error was the absolute value of the static cyclotorsion degree acquired from the AMARIS system plus the deflection degree captured on the screen of the VisuMax system (Figures AC–AD) and measured by angulometer in Adobe Photoshop CS6 (Adobe Inc., San Jose, CA). A clockwise angle of deflection was recorded as a negative degree and a counterclockwise deflection was recorded as a positive degree.

Vector Analysis of Astigmatism

Astigmatic outcomes in the current study were reported according to the Journal of Refractive Surgery standard.26 The vector analysis method of Alpins was used.17,27 Manifest refraction with a vertex distance of 12 mm was converted from spectacle plane to corneal plane. Cylinder axes of left eyes were inverted vertically to avoid the data from left and right eyes canceling out when averaging the data.

Statistical Analysis

The SPSS software (version 20; IBM Corporation, Armonk, NY) was used for statistical analysis. For normally distributed variables (evaluated by the Kolmogorov–Smirnov normality test), the independent samples t test was used for intergroup comparison and the paired t test was performed for the comparison of preoperative and postoperative visits in each group. The Wilcoxon signed-rank test and Mann–Whitney U test were used to compare non-normally distributed variables. Linear scatter plots and the Pearson correlation analysis (or Spearman rank correlation analysis) were applied to assess the association between variables. All values were described as mean ± standard deviation. A P value less than .05 was considered statistically significant.

Results

Basic Characteristics

A total of 142 eyes from 71 patients with bilateral myopic astigmatism who underwent SMILE surgery in Zhongshan Ophthalmic Center of Sun Yat-sen University were included between December 2017 and March 2018. Severe complications occurred in no cases during or after surgery. At 3 months after surgery, 66 patients (93%) with a mean age of 26 years (range: 19 to 39 years) were still available for follow-up. Among them, 45 patients were women and the other 21 were men. Sixty-six eyes in the SCC group and 66 eyes in the control group were available for analysis. There was no significant difference in baseline characteristics, including UDVA, CDVA, sphere, cylinder, and spherical equivalent, between the two groups (Table 1).

Preoperative and Postoperative Visual and Refractive Dataa

Table 1:

Preoperative and Postoperative Visual and Refractive Data

Ocular Cyclotorsion

The average ocular cyclotorsion was 0.60° ± 0.63° (range: 0° to 3.2°) in the SCC group and 3.21° ± 2.33° (range: 0.1° to 10.8°) in the control group (P < .001). Ocular cyclotorsion was 5° or less in 66 eyes (100%) in the SCC group and 53 eyes (77.3%) in the control group.

Visual and Refractive Outcomes

UDVA and CDVA both showed significant improvement in the two groups postoperatively (P < .001). The cylinder and spherical equivalent decreased significantly in both groups after surgery (P < .001). However, as shown in Table 1, there was no statistically significant difference between the two groups in UDVA, CDVA, sphere, cylinder, or spherical equivalent postoperatively.

The efficacy index was 1.05 in the SCC group and 1.07 in the control group (Figures 1A–1B). The safety index was 1.13 in the SCC group and 1.15 in the control group (Figure 1C). Predictability is shown in Figures 1D–1E. A total of 52 eyes (79%) in the SCC group and 57 eyes (86%) in the control group were within ±0.50 D of the targeted refractive astigmatism (Figure 1F).

Visual and refractive outcomes at 3 months after surgery. (A) Cumulative uncorrected distance visual acuity (UDVA) 3 months postoperatively and corrected distance visual acuity (CDVA) preoperatively. (B) Changes in Snellen lines of postoperative UDVA vs preoperative CDVA. (C) Changes in Snellen lines of CDVA postoperatively. (D) Attempted versus achieved spherical equivalent refraction at 3 months postoperatively. (E) Accuracy of spherical equivalent refraction. (F) Comparative amplitude of preoperative and 3-month postoperative astigmatism. (G) Target induced astigmatism vs surgically induced astigmatism vectors 3 months postoperatively. (H) Distribution of refractive astigmatism angle of error at 3 months postoperatively. SCC group = static cyclotorsion compensation; D = diopters

Figure 1.

Visual and refractive outcomes at 3 months after surgery. (A) Cumulative uncorrected distance visual acuity (UDVA) 3 months postoperatively and corrected distance visual acuity (CDVA) preoperatively. (B) Changes in Snellen lines of postoperative UDVA vs preoperative CDVA. (C) Changes in Snellen lines of CDVA postoperatively. (D) Attempted versus achieved spherical equivalent refraction at 3 months postoperatively. (E) Accuracy of spherical equivalent refraction. (F) Comparative amplitude of preoperative and 3-month postoperative astigmatism. (G) Target induced astigmatism vs surgically induced astigmatism vectors 3 months postoperatively. (H) Distribution of refractive astigmatism angle of error at 3 months postoperatively. SCC group = static cyclotorsion compensation; D = diopters

Vector Analysis

The vector analysis of astigmatism is shown in Table 2 using refractive data at 3 months after surgery. No statistically significant difference was found between the two groups in target induced astigmatism (TIA), surgically induced astigmatism (SIA), difference vector, correction index, index of success, angle of error, or magnitude of error. There was a slight undercorrection of astigmatism in the SCC group with the mean correction index less than 1 (correction index = 0.96), and a slight overcorrection of astigmatism in the control group with the mean correction index greater than 1 (correction index = 1.03). There was a slight under-correction of astigmatism in both groups when the TIA was high, with the TIA exceeding the SIA at 3 months (Figure 1G). The angle of error was within ±15° in 60 eyes (91%) in the SCC group and 58 eyes (88%) in the control group (Figure 1H).

Vector Analysis of Astigmatism at 3 Months After Surgerya

Table 2:

Vector Analysis of Astigmatism at 3 Months After Surgery

Aberration Outcomes

The preoperative and postoperative entire eye aberrations were demonstrated as individual Zernike coefficients (Table 3). Limited by pupil size, only values obtained from a 3-mm scan diameter were used. The Zernike polynomials were reported as root mean square values (in micrometers), including astigmatism (C3,C5), defocus (C4), trefoil aberration (C6,C9), coma (C7,C8), and spherical aberration (C12). There were no statistically significant differences between the two groups in the entire eye aberrations preoperatively, except a slightly higher horizontal coma (C8) in the SCC group. However, no significant difference was found in any aberrations between the SCC and control groups 3 months after surgery.

Zernike Coefficients of Preoperative and Postoperative Entire Eye Aberrations in iTrace (Scan Diameter = 3 mm)a

Table 3:

Zernike Coefficients of Preoperative and Postoperative Entire Eye Aberrations in iTrace (Scan Diameter = 3 mm)

Objective Visual Quality Outcomes

The objective visual quality data preoperatively and 3 months postoperatively are shown in Table 4. There was a slight decline in all parameters at 3 months after surgery. However, there was no statistically significant difference between the two groups postoperatively in Objective Scatter Index (P = .803), Strehl ratio (P = .972), and modulation transfer function cut-off (P = .980).

Preoperative and Postoperative Objective Visual Quality in OQASa

Table 4:

Preoperative and Postoperative Objective Visual Quality in OQAS

Contrast Sensitivity Outcomes

Figure 2 shows the preoperative and postoperative contrast sensitivity at spatial frequencies of 3, 6, 12, and 18 cycles per degree (cpd), under four different lighting conditions (photopic, photopic with glare, mesopic, and mesopic with glare lighting condition). The values were all transformed to log contrast sensitivity for calculation. No statistically significant difference was found in contrast sensitivity between the two groups preoperatively or postoperatively.

Contrast sensitivity (CS) at a spatial frequency of 3, 6, 12, and 18 cycles per degree (cpd) under photopic, photopic with glare, mesopic, and mesopic with glare lighting conditions preoperatively and postoperatively. SCC = static cyclotorsion compensation

Figure 2.

Contrast sensitivity (CS) at a spatial frequency of 3, 6, 12, and 18 cycles per degree (cpd) under photopic, photopic with glare, mesopic, and mesopic with glare lighting conditions preoperatively and postoperatively. SCC = static cyclotorsion compensation

Subgroup Analysis

There were a total of 45 eyes in the low astigmatism group, 53 eyes in the moderate astigmatism group, and 34 eyes in the high astigmatism group. In each subgroup, no statistically significant difference was found between the SCC and control groups in visual and refractive outcomes, vector parameters, entire eye aberrations, objective visual quality, or contrast sensitivity.

Discussion

Our study demonstrates that SMILE surgery with or without cyclotorsion compensation offered favorable results in myopic astigmatism correction. Based on the results 3 months postoperatively, we did not find any statistically significant differences between the SCC and control groups in visual and refractive outcomes, astigmatism parameters, entire eye aberrations, objective visual quality, or contrast sensitivity, even in subgroup analysis.

The cyclotorsion of eyes during refractive surgeries had been noticed for a long time. Several studies measured the magnitude of cyclotorsion in various refractive surgeries.16,28–31 Regarding SMILE surgery, the mean ocular cyclotorsion reported by Ganesh et al.23 was 5.64° ± 2.55° (range: 2° to 12°), with 20% of eyes rotated more than 5°. Comparably, the mean cyclotorsion in the control group in our study was 3.21° ± 2.33° (range: 0.1° to 10.8°). It was fairly small, and only 22.7% of eyes showed a cyclotorsion of greater than 5°

Bharti and Bains32 showed that active cyclotorsion error compensation would improve the accuracy of astigmatic correction in LASIK surgery. To the contrary, Lee et al.28 reported that the iris registration group showed no advantages over the non-iris registration group in astigmatism correction, with a compensated cyclotorsion error of 2.1° in wavefront-guided laser epithelial keratomileusis surgery. Analogously, according to our results about SMILE surgery, there was no difference in clinical outcomes between the eyes with or without cyclotorsion compensation. Furthermore, in our control group, no correlation was found between the cyclotorsion error and magnitude of error, angle of error, correction index, or index of success for astigmatic correction. Thus, it could be inferred that ocular cyclotorsion in SMILE surgery was too small to affect the astigmatic outcomes or visual quality.

Prickett et al.33 reported that, compared to postural misalignment, the ocular cyclotorsion was a small component contributing to the total torsional error in refractive surgeries. It was also shown that as long as the surgical position was well controlled, there would be no difference between the eyes with or without iris registration system in astigmatic outcomes.31 In our study, the mean cyclotorsion error in the control group was as small as 3.21°, the correction index of astigmatism was 1.03, and the absolute angle of error was only 6.83°, indicating high precision in astigmatic correction. This was probably owing to our meticulous checking of proper body and head position before the treatment. This may explain why cyclotorsion compensation in SMILE for astigmatic correction was not as advantageous as expected in our study.

In addition to cyclotorsion, several other factors should be emphasized that influence the accuracy of astigmatic correction. Subjective optical zone centration when docking in SMILE may reduce the precision of astigmatic correction. However, this needs further exploration because we did not measure decentration in the current study. The precision of astigmatic treatment with refractive surgery is highly dependent on the reliability of subjective refraction preoperatively. According to Rosenfield and Chiu,34 the mean ± standard deviation and the 95% limits of agreement of the astigmatism axis among five separate measurements was 8.72°and ± 17.1°, which was far greater than the cyclotorsion error during SMILE. In addition, in studies about astigmatic correction with SMILE, a general trend toward undercorrection was found increasing with the preoperative cylinder.4–6 Analogously, according to our subgroup analysis, the correction index of astigmatism was 1.04 in the low astigmatism group, 0.99 in the moderate astigmatism group, and 0.96 in the high astigmatism group. These data implied that the nomogram of SMILE should be optimized, taking the magnitude of preoperative cylinder into account.

The limitations of the current study were its short follow-up period and small sample size for high astigmatism. A longer follow-up time and a larger sample size of high astigmatism (< −3.00 D) in future studies may make the benefits obtained from cyclotorsion compensation more noticeable. Manual limbal marking, which is prone to human error, was used in the current technique. We recommend the use of a totally automated cyclotorsion control system with an active eye tracker for SMILE surgery in cases with an extremely large cyclotorsion error and to evaluate the effect of cyclotorsion compensation more objectively.

This prospective randomized controlled study demonstrated that the ocular rotation in SMILE surgery was small and not sufficient to affect the astigmatic outcomes or postoperative visual quality. The cyclotorsion compensation technique used in this study could help minimize the alignment error, but was not compulsory in SMILE surgery for astigmatic correction as long as the position was well controlled. More attention should be paid to the influence of optical zone decentration, inaccuracy of subjective refraction, and unoptimized nomogram.

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Preoperative and Postoperative Visual and Refractive Dataa

ParameterPreoperativePostoperative (3 Month)


SCC GroupControl GroupPSCC GroupControl GroupP
UDVA (logMAR)1.12 ± 0.22 (0.70 to 1.52)1.11 ± 0.21 (0.70 to 1.52).835b−0.10 ± 0.07 (−0.18 to 0.10)−0.10 ± 0.07 (−0.18 to 0.10).908b
CDVA (logMAR)−0.08 ± 0.07 (−0.18 to 0.05)−0.07 ± 0.06 (−0.18 to 0.05).619b−0.13 ± 0.06 (−0.18 to 0)−0.14 ± 0.06 (−0.18 to 0).981b
Sphere (D)−5.23 ± 1.83 (−9.50 to −0.75)−5.26 ± 1.52 (−9.00 to −2.25).928c0.09 ± 0.38 (−0.75 to 1.25)0.10 ± 0.33 (−0.50 to 1.00).824b
Cylinder (D)−1.52 ± 0.81 (−3.75 to −0.25)−1.57 ± 0.82 (−3.50 to −0.25).689c−0.38 ± 0.28 (−1.00 to 0.00)−0.34 ± 0.30 (−1.25 to 0.00).231b
SE (D)−5.99 ± 1.89 (−11.00 to −2.00)−6.04 ± 1.61 (−10.50 to −3.13).858c−0.10 ± 0.37 (−1.00 to 0.88)−0.07 ± 0.34 (−1.00 to 0.88).582c

Vector Analysis of Astigmatism at 3 Months After Surgerya

ParameterSCC GroupControl GroupP
TIA (D)1.31 ± 0.69 (0.22 to 3.13)1.36 ± 0.69 (0.21 to 2.95).701b
SIA (D)1.26 ± 0.71 (0.17 to 3.13)1.34 ± 0.74 (0.16 to 3.85).514b
Difference vector (D)0.40 ± 0.28 (0.00 to 1.00)0.34 ± 0.30 (0.00 to 1.24).160c
Correction index0.96 ± 0.32 (0.28 to 2.01)1.03 ± 0.30 (0.24 to 1.81).193c
Index of success0.39 ± 0.35 (0.00 to 1.68)0.36 ± 0.51 (0.00 to 2.27).085c
Angle of error (degrees)−3.24 ± 13.55 (−68.00 to 42.00)−3.50 ± 13.47 (−52.00 to 52.00).861c
|Angle of error| (degrees)7.85 ± 11.47 (0.00 to 68.00)6.83 ± 12.10 (0.00 to 52.00).161c
Magnitude of error (degrees)0.05 ± 0.30 (−0.74 to 0.74)0.02 ± 0.33 (−1.24 to 0.73).513b

Zernike Coefficients of Preoperative and Postoperative Entire Eye Aberrations in iTrace (Scan Diameter = 3 mm)a

ParameterPreoperativePostoperative (3 Months)


SCC GroupControl GroupPSCC GroupControl GroupP
C3 (Z2−2)0.15 ± 0.12 (0.00 to 0.52)0.13 ± 0.10 (0.00 to 0.45).284b0.08 ± 0.06 (0.00 to 0.25)0.07 ± 0.07 (0.00 to 0.28).533b
C4 (Z20)2.03 ± 0.54 (0.76 to 3.35)2.04 ± 0.45 (1.16 to 3.23).937b0.25 ± 0.23 (0.00 to 1.38)0.25 ± 0.27 (0.00 to 1.72).646c
C5 (Z22)0.32 ± 0.19 (0.00 to 0.79)0.34 ± 0.20 (0.02 to 0. 81).676b0.12 ± 0.08 (0.00 to 0.35)0.11 ± 0.07 (0.00 to 0.30).418b
C6 (Z3−3)0.04 ± 0.03 (0.00 to 0.12)0.03 ± 0.03 (0.00 to 0.16).453c0.03 ± 0.02 (0.00 to 0.09)0.04 ± 0.03 (0.00 to 0.12).421b
C7 (Z3−1)0.05 ± 0.03 (0.00 to 0.15)0.05 ± 0.04 (0.00 to 0.20).890b0.05 ± 0.04 (0.00 to 0.21)0.04 ± 0.03 (0.00 to 0.13).774b
C8 (Z31)0.03 ± 0.02 (0.00 to 0.09)0.02 ± 0.01 (0.00 to 0.07).021c,d0.03 ± 0.02 (0.00 to 0.10)0.03 ± 0.03 (0.00 to 0.18).465c
C9 (Z33)0.03 ± 0.02 (0.00 to 0.12)0.03 ± 0.03 (0.00 to 0.23).794c0.03 ± 0.02 (0.00 to 0.07)0.02 ± 0.02 (0.00 to 0.07).280b
C12 (Z40)0.02 ± 0.01 (0.00 to 0.06)0.02 ± 0.01 (0.00 to 0.06).232c0.02 ± 0.01 (0.00 to 0.05)0.01 ± 0.01 (0.00 to 0.04).280b

Preoperative and Postoperative Objective Visual Quality in OQASa

ParameterPreoperativePostoperative (3 Months)


SCC GroupControl GroupPSCC GroupControl GroupP
OSI0.50 ± 0.29 (0.10 to 1.80)0.54 ± 0.38 (0.10 to 2.20).772b0.62 ± 0.42 (0.10 to 3.00)0.66 ± 0.44 (0.20 to 2.60).803b
SR0.26 ± 0.07 (0.11 to 0.43)0.26 ± 0.08 (0.09 to 0.49).811c0.22 ± 0.06 (0.10 to 0.40)0.22 ± 0.06 (0.10 to 0.36).972c
MTF cut-off45.14 ± 9.04 (13.86 to 56.35)43.63 ± 9.18 (12.23 to 57.92).344c41.11 ± 8.64 (18.84 to 56.49)41.08 ± 9.00 (20.47 to 56.82).980c
Authors

From Zhongshan Ophthalmic Center, State Key Laboratory of Ophthalmology, Sun Yat-sen University, Guangzhou, China.

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

AUTHOR CONTRIBUTIONS

Study concept and design (JX, FL, ML, XY, LL, QL); data collection (JX, SW, HL, YX); analysis and interpretation of data (JX); writing the manuscript (JX, LL, YX); critical revision of the manuscript (JX, FL, ML, XY, SW, HL, QL)

Correspondence: Quan Liu, MD, PhD, No. 54, Xianlie Road (South), Guangzhou, Guangdong, China. E-mail: drliuquan@163.com

Received: October 31, 2018
Accepted: March 04, 2019

10.3928/1081597X-20190402-01

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