Journal of Refractive Surgery

Original Article Supplemental Data

Results of Intraoperative Manual Cyclotorsion Compensation for Myopic Astigmatism in Patients Undergoing Small Incision Lenticule Extraction (SMILE)

Sri Ganesh, MS, DNB; Sheetal Brar, MS, DNB; Archana Pawar, MS

Abstract

PURPOSE:

To study the safety, efficacy, and outcomes of manual cyclotorsion compensation in small incision lenticule extraction (SMILE) for myopic astigmatism.

METHODS:

Eligible patients with myopia from −1.00 to −10.00 diopters (D) spherical equivalent with a minimum astigmatism of 0.75 D undergoing SMILE were included. Intraoperative cyclotorsion compensation was performed by gently rotating the cone and aligning the 0° to 180° limbal marks with the horizontal axis of the reticule of the right eye piece of the microscope of the femtosecond laser after activating the suction.

RESULTS:

In this study, 81 left eyes from 81 patients were analyzed for vector analysis of astigmatism. The mean cyclotorsion was 5.64° ± 2.55° (range: 2° to 12°). No significant differences were found for surgically induced astigmatism, difference vector, angle of error (AE), correction index, magnitude of error, index of success (IOS), and flattening index between 2 weeks and 3 months postoperatively (P > .05). The eyes were categorized into low (≤ 1.50 D, n = 37) and high (> 1.50 D, n = 44) cylinder groups. At 3 months, intergroup analysis showed a comparable correction index of 0.97 for the low and 0.93 for the high cylinder groups, suggesting a slight undercorrection of 3% and 7%, respectively (P = .14). However, the AE and IOS were significantly lower in the high compared to the low cylinder group (P = .032 and .024 for AE and IOS, respectively), suggesting better alignment of the treatment in the high cylinder group. However, the mean uncorrected distance visual acuity of both groups was comparable (P = .21), suggesting good visual outcomes in the low cylinder group despite a less favorable IOS.

CONCLUSIONS:

Manual compensation may be a safe, feasible, and effective approach to refine the results of astigmatism with SMILE, especially in higher degrees of cylinders.

[J Refract Surg. 2017;33(8):506–512.]

Abstract

PURPOSE:

To study the safety, efficacy, and outcomes of manual cyclotorsion compensation in small incision lenticule extraction (SMILE) for myopic astigmatism.

METHODS:

Eligible patients with myopia from −1.00 to −10.00 diopters (D) spherical equivalent with a minimum astigmatism of 0.75 D undergoing SMILE were included. Intraoperative cyclotorsion compensation was performed by gently rotating the cone and aligning the 0° to 180° limbal marks with the horizontal axis of the reticule of the right eye piece of the microscope of the femtosecond laser after activating the suction.

RESULTS:

In this study, 81 left eyes from 81 patients were analyzed for vector analysis of astigmatism. The mean cyclotorsion was 5.64° ± 2.55° (range: 2° to 12°). No significant differences were found for surgically induced astigmatism, difference vector, angle of error (AE), correction index, magnitude of error, index of success (IOS), and flattening index between 2 weeks and 3 months postoperatively (P > .05). The eyes were categorized into low (≤ 1.50 D, n = 37) and high (> 1.50 D, n = 44) cylinder groups. At 3 months, intergroup analysis showed a comparable correction index of 0.97 for the low and 0.93 for the high cylinder groups, suggesting a slight undercorrection of 3% and 7%, respectively (P = .14). However, the AE and IOS were significantly lower in the high compared to the low cylinder group (P = .032 and .024 for AE and IOS, respectively), suggesting better alignment of the treatment in the high cylinder group. However, the mean uncorrected distance visual acuity of both groups was comparable (P = .21), suggesting good visual outcomes in the low cylinder group despite a less favorable IOS.

CONCLUSIONS:

Manual compensation may be a safe, feasible, and effective approach to refine the results of astigmatism with SMILE, especially in higher degrees of cylinders.

[J Refract Surg. 2017;33(8):506–512.]

The refractive outcome of astigmatism correction has been shown to depend on the accuracy of the axis treatment. Any rotational movement of the eye (cyclotorsion) during treatment may cause a shift in the treatment axis, leading to undesirable results such as undercorrection and induction of aberrations.1–3 Most of the currently available excimer laser platforms have the ability to detect and compensate for the static and dynamic cyclotorsion due to positional changes and treatment by advanced software and eye tracking.1,4

Active cyclotorsion error correction in LASIK improved the accuracy of cylinder correction.4–6 Although there are numerous studies on cyclotorsion and its compensation in LASIK, significant data do not exist for the small incision lenticule extraction (SMILE) procedure. Studies on femtosecond lenticule extraction and SMILE have shown significant undercorrection of astigmatism over time.7–9 The probable explanation of these results could be the unavailability of an active eye tracking software in the VisuMax femtosecond laser system (Carl Zeiss Meditec, Jena, Germany) used to perform these procedures. Because no definite method of cyclotorsion compensation exists for SMILE, this may also be considered a potential limitation of this procedure.

Previous studies on LASIK suggested that manual markings were equally safe and effective as the automated dynamic eye trackers for cyclotorsion compensation during surgery.10 Based on these observations, we attempted to investigate the feasibility of manual compensation for the intraoperative torsional error by using limbal markings as a guide in patients undergoing SMILE for myopic astigmatism.

We describe a simple and practical method for the manual compensation of cyclotorsion during SMILE in patients with significant myopic astigmatism (> 0.75 diopters [D]). We evaluated the safety, efficacy, and reliability of this technique in terms of cylindrical correction and postoperative refractive outcomes in a prospective, interventional study with 3-month follow-up.

Patients and Methods

This prospective, nonrandomized study was approved by our institutional ethics committee and adhered to the tenets of the Declaration of Helsinki. Written informed consent was obtained from all patients participating in the study.

Inclusion criteria were age between 21 and 40 years, myopic astigmatism with up to −10.00 D spherical equivalent (SE) with a minimum astigmatism of 0.75 D, stable refraction (< 0.50 D change in the past 12 months), corrected distance visual acuity (CDVA) of 20/30 or better, healthy ocular surface, absence of corneal ectatic diseases, corneal scars, absence of any retinal pathology likely to affect visual outcomes, and ensured follow-up visits. Eyes with thin corneas (central corneal thickness < 480 µm), diagnosed or suspicious cases of corneal ectatic conditions, severe dry eyes, and contact lens–induced allergy, patients taking systemic steroids, immunosuppressants, oral contraceptives, or antidepressants, and pregnant females were excluded from the study.

Preoperative Evaluation

All patients underwent a thorough preoperative evaluation including anterior and posterior segment examination, cycloplegic and subjective refraction, assessment of uncorrected distance visual acuity (UDVA) and CDVA, corneal topography using the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) and Orbscan II (Bausch & Lomb, Rochester, NY), contrast sensitivity using the Functional Acuity Contrast Test (F.A.C.T. Stereo Optical Co., Inc., Chicago, IL), aberrometry (Hoya iTrace Surgical Workstation; Hoya Surgical Optics, Tokyo, Japan), specular microscopy (Tomey, Nagoya, Japan), and dry eye evaluation (Schirmer 1 and tear film break-up time).

Patients using soft or rigid contact lenses were instructed to discontinue their lenses at least 1 and 3 weeks, respectively, prior to the topographic evaluation.

Treatment Planning

Regardless of the degree of myopia, a 10% overcorrection nomogram was applied to both the spherical and cylindrical components of the refractive error for all eyes.

Surgical Technique

All surgeries were performed by a single experienced refractive surgeon (SG) under topical anesthesia using the VisuMax femtosecond laser, with a pulse repetition rate of 500 kHz, cut energy of 160 nJ with a spot separation of 4.5 µm, 6.5- to 7-mm optical zone, cap thickness of 120 µm, and 2-mm superior incision. The treatment was centered on the visual axis. Mean optical zone used was 6.50 ± 0.23 mm.

Preoperatively, the limbus was marked in the 0° to 180° axis with a dye permitting the transmission of infrared radiation (Viscot surgical skin marker 1436; Viscot Medical, East Hanover, NJ) using either a marker pen or Ganesh bubble marker (Epsilon Surgical, Chino, CA) (Figure A, available in the online version of this article) in the upright position. The patient was then positioned under the VisuMax femtosecond laser and instructed to look into the green flashing fixation light. Once proper centration was achieved, the eye was docked to the patient interface and suction was applied. The extent of cyclotorsion, if any, was determined using the reticule (present in the right eyepiece) and any cyclotorsion (incyclotorsion or excyclotorsion) was manually compensated for by gently rotating the contact glass to align the horizontal marks on the eye to the 0° to 180° axis of the reticule (Figure A and Video 1, available in the online version of this article). Once both were aligned, the active laser process was started to create the refractive lenticule. After lenticule creation by the femtosecond laser, the anterior and posterior lenticule planes were dissected using a blunt dissector, followed by lenticule extraction through the side cut. The interface was washed with balanced salt solution.

(A) Preoperative limbal marking with the Ganesh bubble marker (Epsilon Surgical, Chino, CA) under topical anesthesia in the upright position. This instrument uses three marks on the limbus at 0°, 90°, and 180°, extending 2 mm toward the center of the cornea, which are easy to visualize while the eye is being docked. (B) Method of manual cyclotorsion compensation by a gentle rotation of the cone while holding the same at the attachment of the tube to the cone. (C) Position of the limbal marks (red arrows) under suction ‘ON’ condition without cyclotorsion compensation before starting the laser, showing approximately 12° of cyclotorsion. (D) Final position of the limbal marks after manual compensation of the cyclotorsion error (alignment with the horizontal axis of the eyepiece reticule). Delivery of the laser follows this.

Figure A.

(A) Preoperative limbal marking with the Ganesh bubble marker (Epsilon Surgical, Chino, CA) under topical anesthesia in the upright position. This instrument uses three marks on the limbus at 0°, 90°, and 180°, extending 2 mm toward the center of the cornea, which are easy to visualize while the eye is being docked. (B) Method of manual cyclotorsion compensation by a gentle rotation of the cone while holding the same at the attachment of the tube to the cone. (C) Position of the limbal marks (red arrows) under suction ‘ON’ condition without cyclotorsion compensation before starting the laser, showing approximately 12° of cyclotorsion. (D) Final position of the limbal marks after manual compensation of the cyclotorsion error (alignment with the horizontal axis of the eyepiece reticule). Delivery of the laser follows this.

Postoperative medications included topical 0.3% ofloxacin (Exocin; Allergan, Irvine, CA) four times for 3 days, 0.1% prednisolone acetate eye drops (Pred Forte; Allergan) in tapering dosage for 4 weeks, and lubricants four times for 4 weeks or more.

All surgeries were uneventful and no complications such as suction loss, black spots, difficult dissection, or incomplete separation of lenticule due to the ink marks blocking the laser occurred in any of the eyes.

Patients were followed up at postoperative 1 day, 2 weeks, and 3 months. On all follow-up visits from 2 weeks on, assessment of UDVA, manifest refraction, CDVA, and topography were also performed.

Statistical Analysis

SPSS for Windows software (version 17.0.0; IBM Corporation, Armonk, NY) was used for statistical analysis. All values were expressed as mean ± standard deviation (SD). The independent samples t test was performed for intergroup comparison and the paired t test was used for intragroup comparison of means. A P value of .05 or less was considered statistically significant. Standard refractive graphs were generated using Datagraph-med 5.20 software ( http://www.datagraph.eu).

Vector Analysis of Astigmatism

Only the left eyes were included in the analysis. Astigmatism outcomes were reported according to the standardized format.11–13 Refractive astigmatism at the spectacle plane was converted to the corneal plane using a vertex distance of 12 mm. It was then analyzed with the vector analysis of Alpins using the Assort software (ASSORT Pty. Ltd., Victoria, Australia), with consideration of the change in the astigmatic axis, measuring three vectors and relationships among them. Target induced astigmatism vector (TIA) was defined as the astigmatic change that the surgery was intended to induce, surgically induced astigmatism vector (SIA) was defined as the astigmatic change that the surgery actually induced, and the difference vector (DV) was defined as the induced astigmatic change that would enable the initial surgery to achieve its intended target or the postoperative astigmatism. Magnitude of error (ME) is the arithmetic difference between the SIA and TIA. Angle of error (AE) is the angle between the axis of the SIA and TIA. The flattening index (FI) is a measure of the impact of an astigmatic treatment at off-axis orientation on the astigmatic change at its intended axis.

Results

A total of 81 left eyes from 81 patients were analyzed. The eyes were categorized into low (≤ 1.50 D, n = 37) and high (> 1.50 D, n = 44) cylinder groups, based on the magnitude of preoperative astigmatism. The preoperative patient characteristics are given in Table 1.

Preoperative Baseline Characteristics of Patients (N = 81)a

Table 1:

Preoperative Baseline Characteristics of Patients (N = 81)

Incyclotorsion was more commonly observed (44% of eyes) compared to excyclotorsion (38% of eyes), whereas 18% of eyes did not show any cyclotorsion. However, for convenience of analysis, both incyclotorsion and excyclotorsion were considered broadly as “cyclotorsion” and separate results were not analyzed for incyclotorsion and excyclotorsion.

Overall, the average cyclotorsion observed was 5.64° ± 2.55° (range: 2° to 12°). The magnitude of cyclotorsion was 5° or less in 81%, between 6° and 10° in 17.6%, and 10° or greater in 1.2% of eyes. The mean cyclotorsion was comparable in both the low (5.73° ± 2.8°) and high (5.53° ± 2.29°) cylinder groups, with no statistically significant difference between their values (P = .822) (Table 1).

Visual Outcomes

The mean UDVA showed significant improvement in both groups from 2 weeks to 3 months postoperatively (P < .05 for both groups). However, there was no statistically significant improvement in CDVA in either group over time (Table A, available in the online version of this article).

Visual and Refractive Resultsa

Table A:

Visual and Refractive Results

Efficacy (Postoperative UDVA/Preoperative CDVA)

All eyes had UDVA of 20/32 or better at 3 months, with 84% eyes with UDVA of 20/20 or better (Figure 1). However, the percentage of eyes achieving UDVA of 20/20 or better was higher in the low (95%) versus the high (75%) cylinder group (Figures BC, available in the online version of this article).

Standard graphs for visual outcomes for total eyes. UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity; D = diopters; SEQ = spherical equivalent refraction

Figure 1.

Standard graphs for visual outcomes for total eyes. UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity; D = diopters; SEQ = spherical equivalent refraction

Standard graphs for visual outcomes for high cylinder eyes. UCVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity; D = diopters; SEQ = spherical equivalent refraction

Figure B.

Standard graphs for visual outcomes for high cylinder eyes. UCVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity; D = diopters; SEQ = spherical equivalent refraction

Standard graphs for visual outcomes for low cylinder eyes. UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity; D = diopters; SEQ = spherical equivalent refraction

Figure C.

Standard graphs for visual outcomes for low cylinder eyes. UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity; D = diopters; SEQ = spherical equivalent refraction

Safety (Postoperative CDVA/Preoperative CDVA)

Overall, 56% eyes gained one or more lines of CDVA at the end of the 3-month follow-up (Figure 1). In the high cylinder group, the gain in CDVA was greater (60%) compared to the low cylinder group (54%) (Figures BC). No eye in either group had loss of CDVA compared to preoperative corrected vision.

Refractive Outcomes

The mean SE reduced from −5.00 ± 2.18 D preoperatively to −0.20 ± 0.24 D at the end of the 3-month follow-up (P = .000). A total of 95% eyes were within ±0.50 D, whereas all eyes were within ±1.50 D of SE correction (Figure 2, Table A).

Predictability scatter (attempted vs achieved) of cylindrical refraction with small incision lenticule extraction (SMILE) at 3 months. Data for (A) total (N = 81 eyes), (B) low cylinder (n = 37 eyes), and (C) high cylinder (n = 44 eyes) groups. Above the white line in the middle is overcorrection and below is undercorrection. The red solid line indicates the outcome of linear regression analysis.

Figure 2.

Predictability scatter (attempted vs achieved) of cylindrical refraction with small incision lenticule extraction (SMILE) at 3 months. Data for (A) total (N = 81 eyes), (B) low cylinder (n = 37 eyes), and (C) high cylinder (n = 44 eyes) groups. Above the white line in the middle is overcorrection and below is undercorrection. The red solid line indicates the outcome of linear regression analysis.

Overall, the predictability of cylinder correction was excellent, with all eyes within ±1.00 D of astigmatism correction at 3 months (Figure 2). However, the predictability was slightly better in the low (average deviation: −0.04 D) versus the high (average deviation: −0.21 D) cylinder group, indicating more undercorrection of astigmatism treatment in the latter group (Figure 2).

The postoperative SE and cylinder remained fairly stable, with no significant difference between 2 weeks and 3 months (P > .05) (Figure 1, Figures BC).

Vector Analysis

The vector analysis results of the 81 eyes using 2-week and 3-month refractive data are shown in Tables BC (available in the online version of this article). No significant differences were found for SIA, DV, AE, correction index (CI), ME, IOS, and FI between 2 weeks and 3 months (P > .05).

Vector Analysis of Total (N = 81) Eyes Undergoing SMILE With Manual Cyclotorsion Compensation Postoperatively

Table B:

Vector Analysis of Total (N = 81) Eyes Undergoing SMILE With Manual Cyclotorsion Compensation Postoperatively

Subgroup Analysis of Astigmatic Correction Based on Degree of Target-Induced Astigmatism After SMILE

Table C:

Subgroup Analysis of Astigmatic Correction Based on Degree of Target-Induced Astigmatism After SMILE

Intergroup analysis at 3 months showed that there was no significant difference between the low and high cylinder groups in terms of the DV, CI, ME, and FI. However, the absolute AE and IOS was significantly higher in the low cylinder compared to the high cylinder group (P = .032 and .024 for AE and IOS, respectively) (Figure 3). On the other hand, the ME was higher in the high cylinder compared to the low cylinder group (P = .032) (Tables BC).

Index of success (IOS) for (A) low cylinder and (B) high cylinder groups at 3 months.

Figure 3.

Index of success (IOS) for (A) low cylinder and (B) high cylinder groups at 3 months.

Discussion

Previous studies evaluating astigmatism correction showed superior results with femtosecond laser–assisted LASIK compared to SMILE.14,15 Chan et al.14 showed that the alignment of treatment was more variable in SMILE, leading to a lower efficacy compared to LASIK at 3 months in eyes with low to moderate myopic astigmatism.

Ivarsen et al.16 demonstrated a significant undercorrection of astigmatism and an increased error of treatment with higher attempted cylinder correction. The reported undercorrection was 13% per diopter of attempted cylinder correction in low astigmatic and 16% per diopter in highly astigmatic eyes. This was mainly attributed to noncompensation of errors of cyclotorsion and nonapplication of nomograms during the procedure.

However, in contrast to the study by Ivarsen et al., improved results for astigmatism treatment were achieved in the current study with SMILE. Because we attempted the compensation of cyclotorsion manually and also applied a 10% nomogram (based on the postoperative results of our initial cases of SMILE, which showed undercorrection of up to 1.00 D), the accuracy of astigmatism correction observed was far better compared to the results reported in previous studies.14–16 This was indicated by the high CIs of 0.97 and 0.93 for the low and high cylinder groups, respectively, suggesting an undercorrection of 3% and 7%, respectively, which is approximately 0.25 D, at 3 months. One reason for more undercorrection in the high cylinder group may be a lower mean age compared to the low cylinder group; hence patients in this group were younger with different corneal biomechanics and epithelial healing patterns, which could have given rise to the undercorrection.17 Also, higher degrees of cylinders were shown to have a tendency for greater undercorrection over time.16 However, from a clinical point of view, slight undercorrection would be preferred to overcorrection because a change in the direction of the cylinder axis would probably be poorly accepted by patients.

Although the CI was close to 1 (0.97), the IOS had a higher and thus less favorable numerical value than the high cylinder group, indicating greater misalignment in the low cylinder group. Although the absolute AE and IOS were significantly higher in the low cylinder group compared to the high cylinder group, indicating a suboptimal correction of astigmatism, the visual outcomes in terms of UDVA were similar in both groups at 3 months. This may suggest that it may not be compulsory to manually correct for cyclotorsion in lower degrees of astigmatism in SMILE. The accuracy of treatment of lower degrees of astigmatism would depend on various factors, such as the reliability of preoperative measurement of the magnitude and axis of the cylinder and manual marking, and also assessment of the extent of intraoperative cyclotorsion. Therefore, the advantages of manual compensation in low cylinders may not be ascertained, especially if the intraoperative cyclotorsion is less (< 5°). However, it may have a definite advantage in moderate to high degrees of astigmatism because even minimal meridional errors may have significant negative refractive consequences.18

In this study, the magnitude of intraoperative cyclotorsion was 5° or less in most eyes (81.6%). However, rotation of greater than 5° was found in 18.4% of eyes and 10° or greater in 1.2% of eyes. Studies have shown that rotation of 5° or greater can induce significant undercorrection of the astigmatic component of the refraction and that undercorrection is more noticeable as the degree of astigmatism increases.19,20 Hence, based on the results of this study, we recommend manual compensation of cyclotorsion error for all eyes with high astigmatism (> 1.50 D) with any degree of cyclotorsion and low astigmatism (≤ 1.50 D) with 5° or greater, using the technique described.

In terms of flattening effect achieved, our study showed better FI (0.93) at 3 months compared to the study by Kobashi et al.,21 which showed insufficient flattening with both femtosecond lenticule extraction and SMILE (median flattening indices of 0.79 to 0.80).

There were two potential limitations to this study. First, we did not compare our results with a control group without cyclotorsion compensation. This was done on ethical grounds because we had observed some cases with suboptimal outcomes with high cylinders, and after using this technique our outcomes with astigmatism improved significantly. Second, we determined the postoperative astigmatism at 3 months, when the corneal shape was considered to have been stabilized, taking into account the wound healing responses of the cornea. However, a longer follow-up may be desirable to evaluate the long-term stability of the results obtained with this technique. Also, we did not study the corneal aberrations and their relationship with cylinder undercorrection. The main purpose of the study was to report the outcomes with the technique of manual compensation for cyclotorsion in SMILE because, to the authors' knowledge, this has not been reported earlier. In addition, we wanted to analyze the results of vector analysis of astigmatism with this technique for low cylinder (≤ 1.50 D) and high cylinder (> 1.50 D) eyes, and provide future recommendations for using this technique based on our experience.

Nevertheless, to the best of our knowledge, this is the first preliminary report on the outcomes of astigmatism correction in SMILE using manual compensation. In our experience, gentle rotation of the cone does not lead to loss of suction and no complications occur due to limbal marking. Hence, it may be a safe, simple, and effective approach to improve results of astigmatism with SMILE in the absence of an active eye tracker in the current version of the VisuMax femtosecond laser. However, prospective randomized controlled studies with a longer follow-up may be necessary to confirm the validity of our results.

References

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Preoperative Baseline Characteristics of Patients (N = 81)a

CharacteristicTotal (N = 81)Low Cylinder (n = 37)High Cylinder (n = 44)P
Age (y)27.01 ± 5.8128.37 ± 6.3425.86 ± 5.11.057
SE (D)−5.00 ± 2.18−4.73 ± 1.94−5.23 ± 2.36.299
Cylinder (D)−1.85 ± 0.86−1.11 ± 0.28−2.48 ± 0.66.000
UDVA (logMAR)0.76 ± 0.220.73 ± 0.160.78 ± 0.26.265
CDVA (logMAR)0.017 ± 0.070.016 ± 0.060.018 ± 0.07.905
Intraoperative cyclotorsion
  ≤ 5º81.6%75.67%86.36%
  6° to 9º17.2%21.62%13.63%
  ≥ 10º1.2%2.7%0%
  Mean ± SD5.64 ± 2.555.73 ± 2.85.53 ± 2.29.822
  Range2° to 12°2° to 12°2° to 10°

Visual and Refractive Resultsa

GroupPreoperative2 Weeks Postoperative3 Months Postoperative
Total (N = 81)
  UDVA (logMAR)0.76 ±0.220.00 ± 0.08−0.014 ± 0.08
   Pb.000.001
  CDVA (logMAR)0.017 ± 0.07−0.048 ± 0.06−0.058 ± 0.07
   Pb.000.02
  SE (D)−5.00 ± 2.18−0.20 ±0.35−0.20 ± 0.24
  Range−9.50 to 1.25−1.50 to 0.88−1.25 to 0.50
   Pb.000.922
  Cylinder (D)−1.85 ± 0.86−0.28 ± 0.33−0.28 ± 0.30
  Range−5.00 to −0.75−1.00 to 0.50−1.00 to 0.50
   Pb.0001.00
Low cylinder (n = 37)
  UDVA (logMAR)0.73 ± 0.16−0.016 ± 0.07−0.027 ± 0.07
   Pb.000.044
  CDVA (logMAR)0.016 ± 0.06−0.045 ± 0.08−0.062 ± 0.08
   Pb.000.057
  SE (D)−4.73 ± 1.94−0.17 ± 0.39−0.19 ± 0.25
  Range−9.50 to −1.90−0.88 to 0.88−0.75 to 0.50
   Pb−.000.723
  Cylinder (D)−1.11 ± 0.28−0.20 ± 0.36−0.24 ± 0.30
  Range−1.50 to −0.75−1.00 to 0.50−0.75 to 0.50
   Pb.000.536
High cylinder (n = 44)
  UDVA (logMAR)0.78 ± 0.260.013 ± 0.09−0.004 ± 0.08
   Pb.000.010
  CDVA (logMAR)0.018 ± 0.07−0.050 ± 0.05−0.054 ± 0.06
   Pb.000.160
  SE (D)−5.23 ± 2.36−0.23 ± 0.32−0.21 ± 0.24
  Range−9.38 to −1.25−1.50 to 0.50−1.25 to 0.00
   Pb.000.532
  Cylinder (D)−2.48 ± 0.66−0.34 ± 0.29−0.31 ± 0.31
  Range−5.00 to −1.75−1.00 to 0.00−1.00 to 0.00
   Pb.000.280
High/low cylinder
  UDVA (P)c.120.215
  CDVA (P)c.800.664

Vector Analysis of Total (N = 81) Eyes Undergoing SMILE With Manual Cyclotorsion Compensation Postoperatively

Parameter2 Weeks Postoperative3 Months PostoperativeP
SIA1.53 ± 0.741.55 ± 0.78.364
DV0.33 ± 0.280.29 ± 0.28.071
CI0.95 ± 0.240.96 ± 0.21.683
AE (absolute)4.09 ± 6.053.66 ± 5.88.383
ME−0.108 ± 0.31−0.08 ± 0.29.368
IOS0.24 ± 0.250.20 ± 0.23.071
FI0.92 ± 0.240.93 ± 0.21.460

Subgroup Analysis of Astigmatic Correction Based on Degree of Target-Induced Astigmatism After SMILE

ParameterLow Cylinder (n = 37)High Cylinder (n = 44)P
TIA (preoperative)0.99 ± 0.252.19 ± 0.65.000
SIA0.98 ± 0.302.04 ± 0.72.000
DV0.25 ± 0.250.33 ± 0.30.201
CI0.97 ± 0.260.93 ± 0.15.148
AE (absolute)5.27 ± 7.362.31 ± 3.85.032
ME−0.012 ± 0.23−0.149 ± 0.32.032
IOS0.27 ± 0.290.14 ± 0.15.024
FI0.96 ± 0.260.92 ± 0.16.421
Authors

From Nethradhama Superspeciality Eye Hospital, Bengaluru, Karnataka, India.

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

AUTHOR CONTRIBUTIONS

Study concept and design (SG); data collection (AP); analysis and interpretation of data (SB, AP); writing the manuscript (SB, AP); critical revision of the manuscript (SG, SB); administrative, technical, or material support (SG)

Correspondence: Sheetal Brar, MS, DNB, Nethradhama Superspeciality Eye Hospital, 256/14, Kanakapura Main Road, 7th Block, Jayanagar, Bengaluru, Karnataka 560070, India. E-mail: brar_sheetal@yahoo.co.in

Received: July 27, 2016
Accepted: February 03, 2017

10.3928/1081597X-20170328-01

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