The Impact of 'A Miss Is as Good as a Mile': Is Compensation Necessary for Minimal Ocular Deviation in Myopic Laser Surgery?

Effect of Centration Compensation on Visual Quality in VisuMax 800 SMILE for Small Kappa Angles: A Randomized Trial

The goal of this clinical trial is to evaluate the effect of intraoperative kappa-angle compensation on postoperative visual quality in patients undergoing small incision lenticule extraction (SMILE) using the VisuMax 800 platform. The study will enroll patients with myopia and a kappa-angle offset < 0.2 mm.

The main questions it aims to answer are:

Does intraoperative kappa-angle compensation reduce postoperative higher-order aberrations after SMILE? Does kappa-angle compensation improve postoperative visual quality and refractive outcomes compared with no compensation?

Researchers will compare SMILE with intraoperative kappa-angle compensation to SMILE without compensation to determine whether compensation leads to better optical quality and visual performance.

Participants will:

Undergo SMILE surgery with or without intraoperative kappa-angle compensation Complete scheduled postoperative examinations at 1 week, 1 month, 3 months, and 6 months after surgery Receive measurements of visual acuity, refraction, higher-order aberrations, contrast sensitivity, and safety outcomes

Study Overview

• Status: Not yet recruiting
• Conditions: Myopia; Refractive Ametropia
• Intervention / Treatment: Procedure: Apply no compensation to the Kappa angle; Procedure: Apply compensation to the Kappa angle.

Detailed Description

Angle kappa refers to the offset between the visual axis and the pupil center and may influence the centration of the treatment zone during corneal refractive surgery. Inaccurate centration can lead to decentered ablation and may affect postoperative visual quality, especially higher-order aberrations. With the development of femtosecond laser technology, more precise intraoperative alignment has become possible.

Small incision lenticule extraction (SMILE) is a commonly used corneal refractive procedure with good safety and predictability. The VisuMax 800 system incorporates machine vision-assisted centration guidance, which allows intraoperative adjustment of the treatment center according to the relative position of the corneal vertex and the pupil center. This provides the possibility of performing intraoperative compensation based on the kappa-angle offset.

Previous studies have mainly evaluated centration adjustment in eyes with relatively large kappa-angle offsets and suggested that compensation may improve postoperative optical quality. However, for patients with small offsets, the necessity of intraoperative compensation remains unclear, and prospective randomized clinical trials are limited.

The purpose of this study is to compare the visual outcomes and optical quality after SMILE with or without intraoperative kappa-angle compensation in patients with small kappa-angle offsets.

This study is a single-center, randomized, parallel-group clinical trial. Participants who are suitable for SMILE surgery and have a kappa-angle offset less than 0.2 mm will be enrolled and randomly assigned to receive SMILE with compensation or SMILE without compensation using the VisuMax 800 platform.

All surgeries will be performed by experienced surgeons using standard SMILE procedures. Participants will undergo routine ophthalmic examinations before surgery and will be followed after surgery at scheduled visits.

The main evaluation will assess postoperative visual quality and refractive outcomes. Additional assessments will include visual acuity, refractive accuracy, higher-order aberrations, contrast sensitivity, and safety outcomes.

• Study Type: Interventional
• Enrollment (Estimated): 224
• Phase: Not Applicable

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

1. Patients aged 18 to 40 years with myopia or myopic astigmatism and stable refraction for >=1 year, whose refractive errors fall within the treatable range of and meet the indications for SMILE surgery.
2. Normal corneal morphology and corneal thickness meeting surgical requirements.
3. Preoperative corrected distance visual acuity (CDVA) >= 1.0.
4. Preoperative synthetic Kappa angle offset measured >= 0.10 mm and < 0.20 mm.
5. Voluntarily agree to undergo SMILE surgery on the VISUMAX 800 platform, understand the randomization scheme, and provide signed informed consent.

Exclusion Criteria:

1. History of prior ocular surgery, significant ocular trauma, or presence of corneal or ocular diseases that may affect the safety of refractive surgery.
2. Severe systemic diseases that may affect ocular healing or surgical safety.
3. Females who are pregnant or lactating.
4. Inability to cooperate as required to complete the procedure or follow-up visits.

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
Active Comparator: Non-compensation group; Subjects underwent SMILE surgery on the VisuMax 800 platform. Preoperative offset coordinates (x, y) were measured; however, while preserving the directional sign, no kappa-angle-based laser centration compensation was applied intraoperatively, and the treatment center was set according to the system's default centration method. Except for the difference in compensation strategy, all other surgical procedures and postoperative management were identical to those in the compensation group.	Procedure: Apply no compensation to the Kappa angle; SMILE PRO is an upgraded version/procedural designation of SMILE (Small Incision Lenticule Extraction) performed on the ZEISS VisuMax 800 femtosecond laser platform and remains, in essence, an all-femtosecond corneal refractive procedure. Its basic principle is to use a femtosecond laser to create a lenticule within the corneal stroma together with a small incision, and then remove the lenticule through that incision, thereby reshaping the corneal curvature to correct myopia and astigmatism. In the non-compensation group, no kappa-angle-based laser centration compensation was applied intraoperatively, and the treatment center was set according to the system's default centration method.
Experimental: Compensation group; Subjects underwent SMILE surgery on the VisuMax 800 platform. Preoperative offset coordinates (x, y) were measured, and, while preserving the directional sign, a fixed intraoperative laser centration compensation of 0.1 mm was uniformly applied to all eligible study eyes to achieve a quantitative adjustment of the treatment center toward the visual axis. Except for the difference in compensation strategy, all other surgical procedures and postoperative management were identical to those in the non-compensation group.	Procedure: Apply compensation to the Kappa angle.; SMILE PRO is an upgraded version/procedural designation of SMILE (Small Incision Lenticule Extraction) performed on the ZEISS VisuMax 800 femtosecond laser platform and remains, in essence, an all-femtosecond corneal refractive procedure. Its basic principle is to use a femtosecond laser to create a lenticule within the corneal stroma together with a small incision, and then remove the lenticule through that incision, thereby reshaping the corneal curvature to correct myopia and astigmatism. In the compensation group, during preoperative parameter input, a fixed intraoperative laser centration compensation of 0.1 mm was uniformly applied to all study eyes meeting the inclusion criteria to achieve a quantitative adjustment of the treatment center toward the visual axis.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Coma aberration	Coma aberration measured by wavefront aberrometry to evaluate the effect of intraoperative kappa-angle compensation on postoperative optical quality.	3 months after surgery

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Higher-order aberrations	Total higher-order aberrations, spherical aberration, and trefoil aberration measured using wavefront aberrometry under standardized conditions to evaluate postoperative optical quality.	1 month, 3 months, and 6 months after surgery
Optical zone decentration	Decentration of the optical zone measured using corneal topography by determining the displacement between the optical zone center and the corneal vertex.	3 months after surgery
Visual acuity	Binocular uncorrected distance visual acuity and corrected distance visual acuity measured using standardized visual acuity charts to evaluate visual performance and safety.	1 month, 3 months, and 6 months after surgery
Manifest refraction	Postoperative sphere, cylinder, and spherical equivalent measured by manifest refraction.	1 month, 3 months, and 6 months after surgery
Refractive accuracy	Proportion of eyes within predefined ranges of target refraction to evaluate refractive predictability.	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 visits.	1 month to 6 months after surgery
Contrast sensitivity	Contrast sensitivity will be measured using a standardized contrast sensitivity testing system (CSV-1000, VectorVision, USA) at multiple spatial frequencies.	3 months after surgery
Quality of Vision (QoV) score	Visual symptoms will be assessed using the Quality of Vision (QoV) questionnaire, which evaluates the frequency, severity, and bothersome nature of visual disturbances. Scores are recorded on ordinal scales, with higher scores indicating worse visual quality.	3 months after surgery
Patient satisfaction score	Patient satisfaction will be assessed using a 5-point rating scale. Scores range from 1 to 5, with higher scores indicating greater satisfaction.	3 months after surgery
Adverse events	Incidence of intraoperative or postoperative complications, including loss of corrected distance visual acuity and other clinically significant events.	Up to 6 months after surgery

Collaborators and Investigators

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

Publications and helpful links

General Publications

• McAlinden C, Pesudovs K, Moore JE. The development of an instrument to measure quality of vision: the Quality of Vision (QoV) questionnaire. Invest Ophthalmol Vis Sci. 2010 Nov;51(11):5537-45. doi: 10.1167/iovs.10-5341. Epub 2010 May 26.
• Doostparast A, Ghandhari M, Rastegar M, Khosronejad AH, Ghandhari M, Eslampoor A. Distribution and inter-device agreement of chord mu/alpha lengths and axes between Pentacam HR, Sirius, and IOLMaster 700. Photodiagnosis Photodyn Ther. 2025 Dec;56:105275. doi: 10.1016/j.pdpdt.2025.105275. Epub 2025 Nov 6.
• Shao T, Wang Y, Ng ALK, Chan TCY, Hao W, Zhang J, Cheng GPM, Jhanji V. The Effect of Intraoperative Angle Kappa Adjustment on Higher-Order Aberrations Before and After Small Incision Lenticule Extraction. Cornea. 2020 May;39(5):609-614. doi: 10.1097/ICO.0000000000002274.
• Lai X, Liu X, Zeng T, Huang Y, Yang X. Comparison of visual outcomes and optical aberrations after SMILE with intraoperative Kappa angle adjustments between small and large Kappa angles. Sci Rep. 2024 Jun 24;14(1):14551. doi: 10.1038/s41598-024-65366-w.
• Deng M, Zhou D, Li M, Shi Y, Sun L, Zou J, Ma X. Evaluation of corneal asymmetry and higher-order aberrations after small incision lenticule extraction for moderate and high myopia. Int Ophthalmol. 2025 Jun 1;45(1):218. doi: 10.1007/s10792-025-03576-5.
• Vingopoulos F, Zisimopoulos A, Kanellopoulos AJ. Comparison of effective corneal refractive centration to the visual axis: LASIK vs SMILE, a contralateral eye digitized comparison of the postoperative result. J Cataract Refract Surg. 2021 Dec 1;47(12):1511-1518. doi: 10.1097/j.jcrs.0000000000000687.
• Chang JS, Law AK, Ng JC, Chan VK. Comparison of refractive and visual outcomes with centration points 80% and 100% from pupil center toward the coaxially sighted corneal light reflex. J Cataract Refract Surg. 2016 Mar;42(3):412-9. doi: 10.1016/j.jcrs.2015.09.030.

Study record dates

Study Major Dates

• Study Start (Estimated): April 1, 2026
• Primary Completion (Estimated): May 30, 2027
• Study Completion (Estimated): May 30, 2027

Study Registration Dates

• First Submitted: March 21, 2026
• First Submitted That Met QC Criteria: March 31, 2026
• First Posted (Actual): April 6, 2026

Study Record Updates

• Last Update Posted (Actual): April 6, 2026
• Last Update Submitted That Met QC Criteria: March 31, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: SMILE; Randomized Clinical Trial; myopia; Refractive Surgery; Angle Kappa; VisuMax 800
• Additional Relevant MeSH Terms: Eye Diseases; Refractive Errors; Myopia
• Other Study ID Numbers: IIT2025199

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