Comparison of Two Rotational Alignment Methods for Astigmatism Correction in SMILE Surgery

Comparison of Astigmatic Correction Outcomes Following SMILE With OcuLign-Assisted Cyclotorsion Control and Manual Limbal Marking: A Prospective Randomized Contralateral-Eye Noninferiority Study

Small incision lenticule extraction (SMILE) is a commonly used corneal refractive procedure for correcting myopia and myopic astigmatism. During astigmatism correction, eye rotation between the upright examination position and the supine surgical position may affect the alignment of the astigmatic treatment axis and may contribute to residual astigmatism after surgery.

Manual limbal marking is a commonly used method to guide cyclotorsion adjustment during refractive surgery. OcuLign is an assisted cyclotorsion control function of the VISUMAX 800 platform that helps identify ocular rotation and guide axis alignment during SMILE. However, direct clinical evidence comparing OcuLign-assisted cyclotorsion control with manual limbal marking during SMILE is limited.

This study is a single-center, prospective, randomized, masked, contralateral-eye non-inferiority trial. Adults aged 18 to 40 years with stable myopia and astigmatism who plan to undergo bilateral SMILE surgery will be enrolled. In each participant, one eye will receive SMILE with OcuLign-assisted cyclotorsion control, and the fellow eye will receive SMILE with manual limbal marking-guided cyclotorsion adjustment. The treatment assigned to the right eye will be determined by randomization.

The primary objective is to compare residual refractive astigmatism at 3 months after surgery between the two methods. Secondary outcomes include visual acuity, refractive predictability and stability, astigmatism vector analysis, higher-order aberrations, contrast sensitivity, patient-reported quality of vision, overall satisfaction, and safety outcomes. Participants will be followed for approximately 6 months after surgery.

Study Overview

• Status: Not yet recruiting
• Conditions: Myopia; Refractive Ametropia
• Intervention / Treatment: Procedure: Device-assisted cyclotorsion control during SMILE; Procedure: Manual limbal marking-guided cyclotorsion adjustment during SMILE

Detailed Description

Accurate alignment of the astigmatic treatment axis is an important factor in the correction of myopic astigmatism during small incision lenticule extraction (SMILE). Cyclotorsion may occur when a patient changes from the upright preoperative examination position to the supine surgical position, and may also be influenced by fixation, head position, and suction during surgery. Inadequate compensation for ocular rotation may reduce astigmatic correction accuracy and contribute to postoperative residual astigmatism.

Manual limbal marking is a commonly used method for cyclotorsion adjustment in corneal refractive surgery. This method is clinically feasible and widely used, but it depends on preoperative marking and intraoperative manual judgment. Marking clarity, ocular surface conditions, patient cooperation, and surgeon experience may affect the accuracy and reproducibility of the adjustment. OcuLign is an assisted cyclotorsion control function of the VISUMAX 800 platform that helps identify ocular rotation and guide axis alignment during SMILE. This study is designed to compare OcuLign-assisted cyclotorsion control with manual limbal marking-guided cyclotorsion adjustment during SMILE.

This trial uses a prospective, randomized, contralateral-eye non-inferiority design. Each participant will undergo bilateral SMILE surgery. One eye will be assigned to OcuLign-assisted cyclotorsion control, and the fellow eye will be assigned to manual limbal marking-guided cyclotorsion adjustment, according to a prespecified randomization sequence. This paired-eye design is intended to reduce inter-individual variability in refractive characteristics, healing response, and subjective visual perception. Apart from the method of cyclotorsion adjustment, surgical parameters, lenticule design, suction procedure, postoperative medication, and follow-up schedule will be kept consistent between the two eyes.

Participants and postoperative outcome assessors will be masked to the eye-level treatment assignment whenever feasible. The operating surgeon cannot be masked because the assigned cyclotorsion adjustment method must be performed during surgery. Postoperative assessments will be conducted at predefined follow-up visits through approximately 6 months after surgery.

The primary comparison will evaluate whether OcuLign-assisted cyclotorsion control is non-inferior to manual limbal marking-guided adjustment in terms of residual refractive astigmatism at 3 months after surgery. Secondary assessments will evaluate visual acuity, refractive predictability and stability, astigmatism vector parameters, higher-order aberrations, contrast sensitivity, patient-reported quality of vision, satisfaction, and safety. Safety monitoring will include loss of corrected distance visual acuity and postoperative adverse events.

• Study Type: Interventional
• Enrollment (Estimated): 52
• Phase: Not Applicable

Contacts and Locations

Study Locations

• China
  • Guangdong
    • Guangzhou, Guangdong, China, 510060
      • Zhongshan Ophthalmic Center

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

1. Age range: 18 - 40 years old. Patients with myopic astigmatism and stable refractive status for >= 1 year.
2. Normal corneal morphology in both eyes, with corneal thickness and other ocular parameters meeting the requirements for SMILE surgery.
3. Preoperative corrected distance visual acuity (CDVA) >= 1.0 in both eyes.
4. Manifest refractive cylinder >= 0.75 D in both eyes, with an interocular difference in absolute cylinder power <= 1.00 D.
5. Both eyes can provide reliable preoperative upright-position image information required for astigmatic axis recognition, and are judged by the investigator to meet the requirements for OcuLign cyclotorsion recognition and axis alignment on the VISUMAX 800 platform.
6. Voluntary to undergo bilateral SMILE surgery on the VISUMAX 800 platform, understanding the random eye-assignment scheme and signing the informed consent form.

Exclusion Criteria:

1. History of prior ocular surgery, significant ocular trauma, or presence of ocular diseases that may affect the safety of refractive surgery or the interpretation of study outcomes.
2. Irregular astigmatism or poor repeatability of bilateral astigmatism measurements, making reliable astigmatic axis analysis impossible.
3. Presence of strabismus, nystagmus, significant binocular vision abnormality, or any condition that may affect fixation or cooperation during examinations.
4. Severe systemic diseases that may affect ocular healing or surgical safety.
5. Females who are pregnant or lactating.
6. Inability to complete the required postoperative follow-up visits or questionnaire assessments.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Double

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: OcuLign-Assisted Cyclotorsion Control; One eye of each participant will undergo SMILE using OcuLign-assisted cyclotorsion control on the VISUMAX 800 platform. OcuLign will be used intraoperatively to assist in identifying ocular rotation and guiding astigmatic axis alignment. Apart from the cyclotorsion adjustment method, the surgical parameters, lenticule design, suction procedure, postoperative medication, and follow-up schedule will be the same as those used for the fellow eye.	Procedure: Device-assisted cyclotorsion control during SMILE; One eye of each participant will undergo SMILE using device-assisted cyclotorsion control with the OcuLign function of the VISUMAX 800 platform. During surgery, OcuLign will assist in identifying ocular rotation and guiding astigmatic axis alignment. Apart from the cyclotorsion adjustment method, the surgical parameters, lenticule design, suction procedure, postoperative medication, and follow-up schedule will be the same as those used for the fellow eye.; Other Names: OcuLign-assisted cyclotorsion control; VISUMAX 800 OcuLign
Active Comparator: Manual Limbal Marking-Guided Adjustment; The fellow eye of each participant will undergo SMILE using manual limbal marking-guided cyclotorsion adjustment. Limbal reference marks will be made in the upright preoperative position, and intraoperative axis alignment will be manually adjusted according to the marks and the surgical reference direction. Apart from the cyclotorsion adjustment method, the surgical parameters, surgical procedure, postoperative medication, and follow-up schedule will be the same as those used for the contralateral eye.	Procedure: Manual limbal marking-guided cyclotorsion adjustment during SMILE; The fellow eye of each participant will undergo SMILE using manual limbal marking-guided cyclotorsion adjustment. Limbal reference marks will be made in the upright preoperative position, and intraoperative axis alignment will be manually adjusted according to the limbal marks and the surgical reference direction. Apart from the cyclotorsion adjustment method, the surgical parameters, surgical procedure, postoperative medication, and follow-up schedule will be the same as those used for the contralateral eye.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Residual refractive astigmatism	Residual refractive astigmatism will be measured as the absolute manifest cylinder power in diopters at 3 months after SMILE. The primary analysis will compare residual refractive astigmatism between eyes treated with OcuLign-assisted cyclotorsion control and eyes treated with manual limbal marking-guided cyclotorsion adjustment to evaluate non-inferiority.	3 months after surgery

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Astigmatic correction predictability	Astigmatic correction predictability will be assessed as the proportion of eyes with postoperative residual manifest cylinder within predefined thresholds, including ≤0.25 D, ≤0.50 D, and ≤1.00 D.	1 month, 3 months, and 6 months after surgery
Astigmatism vector analysis parameters	Astigmatism correction will be evaluated using vector analysis based on the Alpins method. Parameters will include target-induced astigmatism, surgically induced astigmatism, difference vector, angle of error, magnitude error, correction index, and index of success.	3 months after surgery
Visual acuity	Uncorrected distance visual acuity and corrected distance visual acuity will be measured using standardized visual acuity charts and recorded as logMAR visual acuity. Visual acuity-derived performance will also be summarized using the safety index and efficacy index, calculated from the same visual acuity measurements. The safety index is defined as postoperative corrected distance visual acuity divided by preoperative corrected distance visual acuity, and the efficacy index is defined as postoperative uncorrected distance visual acuity divided by preoperative corrected distance visual acuity.	1 month, 3 months, and 6 months after surgery
Manifest refraction	Postoperative manifest refraction will include sphere, cylinder, and spherical equivalent measured by standard manifest refraction.	1 month, 3 months, and 6 months after surgery
Refractive accuracy	Refractive accuracy will be assessed as the proportion of eyes with postoperative spherical equivalent within predefined ranges of the target refraction, including within ±0.25 D, ±0.50 D, and ±1.00 D.	1 month, 3 months, and 6 months after surgery
Refractive stability	Refractive stability will be assessed as the change in manifest spherical equivalent refraction between postoperative follow-up visits.	1 month to 6 months after surgery
Higher-order aberrations	Higher-order aberrations will be measured using wavefront aberrometry under standardized conditions. Parameters will include total higher-order aberrations, coma aberration, spherical aberration, and trefoil aberration.	1 month, 3 months, and 6 months after surgery
Contrast sensitivity	Contrast sensitivity will be measured under standardized conditions using the CSV-1000 contrast sensitivity testing system at multiple spatial frequencies, including 3, 6, 12, and 18 cycles per degree. The area under the log contrast sensitivity function may be calculated as a summary measure when appropriate.	3 months after surgery
Quality of Vision score	Subjective visual symptoms will be assessed using the Quality of Vision questionnaire, which evaluates the frequency, severity, and bothersome nature of visual disturbances such as glare, halos, and double vision. Higher scores indicate worse subjective visual quality.	3 months after surgery
Overall visual satisfaction score	Overall visual satisfaction will be assessed using a 5-point Likert rating scale. Scores range from 1 to 5, with higher scores indicating greater satisfaction.	3 months after surgery

Collaborators and Investigators

• Sponsor: Zhongshan Ophthalmic Center, Sun Yat-sen University

Publications and helpful links

General Publications

• Chen P, Ye Y, Yu N, Zhang X, He J, Zheng H, Wei H, Zhuang J, Yu K. Comparison of Small Incision Lenticule Extraction Surgery With and Without Cyclotorsion Error Correction for Patients With Astigmatism. Cornea. 2019 Jun;38(6):723-729. doi: 10.1097/ICO.0000000000001937.
• Wang B, Wang Y, Zhang J. Comparison of astigmatic correction with and without limbal marking during small-incision lenticule extraction. J Cataract Refract Surg. 2022 Aug 1;48(8):924-928. doi: 10.1097/j.jcrs.0000000000000889.
• Yang X, Liu Y, Xiao K, Song Q, Xu Y, Li J, Zhou Y. Effect of Cyclotorsion Compensation in Small Incision Lenticule Extraction Surgery for the Correction of Myopic Astigmatism: A Systematic Review and Meta-Analysis. Ophthalmol Ther. 2024 May;13(5):1271-1288. doi: 10.1007/s40123-024-00921-2. Epub 2024 Mar 18.

Study record dates

Study Major Dates

• Study Start (Estimated): July 13, 2026
• Primary Completion (Estimated): June 30, 2027
• Study Completion (Estimated): June 30, 2027

Study Registration Dates

• First Submitted: July 6, 2026
• First Submitted That Met QC Criteria: July 6, 2026
• First Posted (Actual): July 10, 2026

Study Record Updates

• Last Update Posted (Actual): July 10, 2026
• Last Update Submitted That Met QC Criteria: July 6, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: SMILE; myopia; Cyclotorsion; VisuMax 800
• Additional Relevant MeSH Terms: Eye Diseases; Refractive Errors; Myopia
• Other Study ID Numbers: IIT2026071

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No