The goal of this clinical trial is to compare two intraoperative kappa-angle compensation strategies during small incision lenticule extraction (SMILE) using the VisuMax 800 platform in patients with relatively large kappa-angle offsets.
Angle kappa represents the difference between the visual axis and the pupil center. In patients with a large offset, pupil-centered treatment may lead to decentration of the optical zone, which can induce higher-order aberrations and affect postoperative visual quality. The VisuMax 800 system allows intraoperative adjustment of the treatment center based on the measured offset, making different compensation strategies possible.
The main questions this study aims to answer are:
Does low kappa-angle compensation (50%) result in lower postoperative higher-order aberrations than high compensation (100%)? Does the compensation strategy influence visual acuity, refractive outcomes, contrast sensitivity, and subjective visual quality after SMILE? Are the measurements obtained from different diagnostic devices consistent when evaluating kappa-related parameters?
Researchers will compare SMILE with low compensation to SMILE with high compensation to determine which strategy provides better optical quality and visual performance.
Participants will:
Undergo SMILE surgery using either low or high kappa-angle compensation Complete scheduled postoperative examinations at 1 month, 3 months, and 6 months Receive measurements of visual acuity, refraction, higher-order aberrations, contrast sensitivity, and patient-reported visual outcomes Be monitored for safety outcomes and adverse events during follow-up
Age range: 18 - 40 years old. Patients with stable refractive status for >= 1 year, having myopia or myopic astigmatism, with refractive power within the range of SMILE procedure.
Normal corneal morphology and corneal thickness meeting the surgical requirements.
Best corrected visual acuity (CDVA) before surgery >= 1.0.
The kappa angle-related offset coordinates (x, y) obtained before surgery, with the absolute value of either |x| or |yl| of any eye >= 0.20mm.
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.
Parallel
Apply high compensation to the Kappa angle.
Procedure/SurgerySMILE PRO is an upgraded version/procedural designation of SMILE (Small Incision Lenticule Extraction) performed on the ZEISS VisuMax 800 femtosecond laser platform. It 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 high-level compensation group, a high level of compensation for the kappa angle was applied during the preoperative parameter input.
Apply low compensation to the Kappa angle.
Procedure/SurgerySMILE PRO is an upgraded version/procedural designation of SMILE (Small Incision Lenticule Extraction) performed on the ZEISS VisuMax 800 femtosecond laser platform. It is essentially an all-femtosecond corneal refractive procedure. Its basic principle is to use a femtosecond laser to create a lenticule within the corneal stroma and a small incision, and then remove the lenticule through the incision, thereby reshaping the corneal curvature to correct myopia and astigmatism. In the low-level compensation group, a low level of kappa-angle compensation was applied during the preoperative parameter input.
Coma aberration
Coma aberration measured by wavefront aberrometry to evaluate the effect of intraoperative kappa-angle compensation on postoperative optical quality.
Higher-order aberrations
Total higher-order aberrations, spherical aberration, and trefoil aberration measured using wavefront aberrometry under standardized conditions to evaluate postoperative optical quality.
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.
Visual Acuity
Binocular uncorrected distance visual acuity and corrected distance visual acuity measured using standardized visual acuity charts to evaluate visual performance and safety.
Manifest refraction
Postoperative sphere, cylinder, and spherical equivalent measured by manifest refraction.
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