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

Official title

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

Overview

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.

Interventions

• 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
• 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

Primary outcome measures

• Coma aberration [Time frame: 3 months after surgery]

Secondary outcome measures (10)

• Higher-order aberrations [Time frame: 1 month, 3 months, and 6 months after surgery]
• Optical zone decentration [Time frame: 3 months after surgery]
• Visual acuity [Time frame: 1 month, 3 months, and 6 months after surgery]
• Manifest refraction [Time frame: 1 month, 3 months, and 6 months after surgery]
• Refractive accuracy [Time frame: 1 month, 3 months, and 6 months after surgery]
• Refractive stability [Time frame: 1 month to 6 months after surgery]
• Contrast sensitivity [Time frame: 3 months after surgery]
• Quality of Vision (QoV) score [Time frame: 3 months after surgery]
• Patient satisfaction score [Time frame: 3 months after surgery]
• Adverse events [Time frame: Up to 6 months after surgery]

Eligibility criteria

Inclusion criteria

• 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.
• Normal corneal morphology and corneal thickness meeting surgical requirements.
• Preoperative corrected distance visual acuity (CDVA) >= 1.0.
• Preoperative synthetic Kappa angle offset measured >= 0.10 mm and < 0.20 mm.
• Voluntarily agree to undergo SMILE surgery on the VISUMAX 800 platform, understand the randomization scheme, and provide signed informed consent.

Exclusion criteria

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

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: No

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Double blind

Primary purpose

Treatment

Study locations

China · 1 center

• Zhongshan Ophthalmic Center — Guangzhou

Publications

• 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. PMID 41205666
• 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. PMID 32040010
• 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. PMID 38914606
• 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. PMID 40451982
• 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. PMID 34074993
• 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. PMID 20505205
• 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. PMID 27063522

Identifiers

NCT: NCT07512115 · IIT2025199

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗