Myopia, Refractive Ametropia
Conditions
Keywords
myopia, SMILE, Refractive Surgery, Randomized Clinical Trial, Angle Kappa, VisuMax 800
Brief summary
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
Detailed description
Angle kappa refers to the offset between the visual axis and the pupil center and is an important factor influencing the centration of the treatment zone during corneal refractive surgery. In patients with relatively large offsets, pupil-centered treatment may lead to decentered lenticule extraction, which can induce higher-order aberrations, especially coma, and may reduce postoperative visual quality. Small incision lenticule extraction (SMILE) is a widely used corneal refractive procedure with good safety and predictability. The new-generation VisuMax 800 femtosecond laser system incorporates machine vision-assisted alignment, allowing the surgeon to adjust the treatment center according to the measured displacement between the corneal vertex and the pupil center. This enables intraoperative compensation based on the kappa-angle offset. Previous studies in excimer laser surgery have evaluated different proportions of kappa-angle compensation, but prospective randomized studies in SMILE are limited, particularly in patients with relatively large offsets. In addition, the optimal amount of compensation during SMILE has not been clearly determined. This study is a single-center, randomized, parallel-group clinical trial designed to compare two predefined compensation strategies during SMILE using the VisuMax 800 platform. Patients aged 18-40 years with stable myopia or myopic astigmatism and a kappa-related displacement of at least 0.20 mm will be enrolled and randomly assigned to one of two groups. Participants in the low-compensation group will undergo SMILE with the treatment center shifted by 50% of the measured offset coordinates, while participants in the high-compensation group will undergo SMILE with 100% compensation of the measured offset. All surgeries will be performed using the same surgical protocol, and postoperative management will be identical in both groups. Participants will undergo routine ophthalmic examinations before surgery and at scheduled follow-up visits after surgery. The primary evaluation will assess postoperative higher-order aberrations at 3 months. Secondary evaluations will include visual acuity, refractive outcomes, refractive stability, contrast sensitivity, patient-reported visual quality, optical zone centration, and safety outcomes. In addition, measurements obtained from different diagnostic devices will be compared to assess consistency. The results of this study will help determine the optimal intraoperative compensation strategy for SMILE in patients with large kappa-angle offsets and may contribute to improving postoperative visual quality and refractive accuracy.
Interventions
PROCEDUREApply high 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. 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.
PROCEDUREApply low 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. 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.
Sponsors
Zhongshan Ophthalmic Center, Sun Yat-sen University
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
TREATMENT
Masking
DOUBLE (Subject, Outcomes Assessor)
Eligibility
Sex/Gender
ALL
Age
18 Years to 40 Years
Healthy volunteers
No
Inclusion criteria
1. 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. 2. Normal corneal morphology and corneal thickness meeting the surgical requirements. 3. Best corrected visual acuity (CDVA) before surgery \>= 1.0. 4. 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. 5. Voluntary to undergo SMILE surgery on the VISUMAX800 platform, understanding the random grouping scheme and signing the informed consent form.
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.
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Coma aberration | 3 months after surgery | Coma aberration measured by wavefront aberrometry to evaluate the effect of intraoperative kappa-angle compensation on postoperative optical quality. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Higher-order aberrations | 1 month, 3 months, and 6 months after surgery | Total higher-order aberrations, spherical aberration, and trefoil aberration measured using wavefront aberrometry under standardized conditions to evaluate postoperative optical quality. |
| Optical zone decentration | 3 months after surgery | Decentration of the optical zone measured using corneal topography by determining the displacement between the optical zone center and the corneal vertex. |
| Visual Acuity | 1 month, 3 months, and 6 months after surgery | Binocular uncorrected distance visual acuity and corrected distance visual acuity measured using standardized visual acuity charts to evaluate visual performance and safety. |
| Manifest refraction | 1 month, 3 months, and 6 months after surgery | Postoperative sphere, cylinder, and spherical equivalent measured by manifest refraction. |
| Refractive accuracy | 1 month, 3 months, and 6 months after surgery | Proportion of eyes within predefined ranges of target refraction to evaluate refractive predictability. |
| Refractive stability | 1 month to 6 months after surgery | Refractive stability will be assessed as the change in manifest spherical equivalent refraction between postoperative visits. |
| Contrast sensitivity | 3 months after surgery | Contrast sensitivity will be measured using a standardized contrast sensitivity testing system (CSV-1000, VectorVision, USA) at multiple spatial frequencies. |
| Quality of Vision (QoV) score | 3 months after surgery | 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. |
| Patient satisfaction score | 3 months after surgery | Patient satisfaction will be assessed using a 5-point rating scale. Scores range from 1 to 5, with higher scores indicating greater satisfaction. |
| Adverse events | Up to 6 months after surgery | Incidence of intraoperative or postoperative complications, including loss of corrected distance visual acuity and other clinically significant events. |
Countries
China
Outcome results
None listed