NCT07512115

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

• Status: Not Yet Recruiting
• Phase: N/A
• Study type: Interventional
• Enrollment: 224 (estimated)
• Sponsor: Zhongshan Ophthalmic Center, Sun Yat-sen University · Academic / Other
• Sex: All
• Age: 18 Years – 40 Years
• Healthy volunteers: Not accepted

Summary

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

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.

Conditions

• Myopia
• Refractive Ametropia

Interventions

Type	Name	Description
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.
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.

Timeline

• Start date: 2026-04-01
• Primary completion: 2027-05-30
• Completion: 2027-05-30
• First posted: 2026-04-06
• Last updated: 2026-04-06