This prospective interventional study aims to evaluate the long-term refractive and visual quality outcomes of SMILE PRO surgery in patients with myopia and high astigmatism. Eligible participants undergo small incision lenticule extraction using the VisuMax 800 femtosecond laser. Postoperative assessments include uncorrected and corrected distance visual acuity, manifest refraction, astigmatic vector analysis, contrast sensitivity, and higher-order aberrations. Participants are followed for up to 12 months to assess refractive accuracy, stability, safety, and visual quality after surgery.
This is a single-center, prospective interventional clinical study conducted to assess the long-term refractive and visual quality outcomes of SMILE PRO surgery for the correction of myopia with high astigmatism. The study is performed at Hong Son Eye Hospital, Vietnam, following approval from the Institutional Review Board of Hanoi Medical University. All participants provide written informed consent prior to enrollment. Patients aged 18 to 40 years with stable myopic refractive error and high astigmatism are eligible for inclusion. All eyes undergo small incision lenticule extraction using the VisuMax 800 femtosecond laser according to a standardized surgical protocol. Manifest refraction, corneal topography, and ocular imaging are performed by experienced refractive technicians using standardized measurement protocols. All patients are examined preoperatively and postoperatively by an ophthalmologist, who reviews clinical findings and surgical eligibility. All SMILE PRO procedures are performed by the same ophthalmic surgeon to minimize variability related to surgical technique. Outcome measures include uncorrected and corrected distance visual acuity, spherical equivalent refraction, residual refractive astigmatism, and astigmatic vector analysis based on the Alpins method. Visual quality outcomes are further evaluated using contrast sensitivity testing and wavefront aberrometry to assess higher-order aberrations. Intraoperative parameters, including centration and cyclotorsion, are recorded and analyzed for their potential association with postoperative refractive outcomes. Postoperative examinations are performed at 1 week, 1 month, 3 months, 6 months, and 12 months after surgery. The primary objective of this study is to evaluate the long-term refractive accuracy, stability, and safety of SMILE PRO surgery in eyes with high astigmatism. Secondary objectives include the assessment of preoperative and intraoperative factors influencing postoperative visual and refractive outcomes.
Study Type
INTERVENTIONAL
Small incision lenticule extraction surgery performed using the VisuMax 800 femtosecond laser (SMILE PRO) for the correction of myopia with high astigmatism. The procedure is performed by a single experienced ophthalmic surgeon following a standardized surgical protocol.
Hong Son Eye Hospital
Hanoi, Hanoi, Vietnam
Residual Refractive Astigmatism
Residual refractive astigmatism was measured using manifest refraction and analyzed with astigmatic vector analysis based on the Alpins method.
Time frame: 12 months postoperatively
Refractive Accuracy (Spherical Equivalent Error)
Refractive accuracy was assessed using manifest refraction spherical equivalent (SEQ) after SMILE PRO surgery.
Time frame: 12 months postoperatively
Refractive Stability Over Time (Spherical Equivalent)
Manifest refraction spherical equivalent (SEQ) was measured at each postoperative visit to evaluate refractive stability.
Time frame: 1 week, 1 month, 3 months, 6 months, and 12 months postoperatively
Refractive Cylinder Over Time
Manifest refractive cylinder was measured using subjective refraction and expressed in diopters (D) at scheduled postoperative visits following SMILE Pro surgery. This outcome evaluates the magnitude and stability of residual astigmatism during the 12-month follow-up period.
Time frame: 1 week, 1 month, 3 months, 6 months, and 12 months postoperatively
Uncorrected Distance Visual Acuity (UDVA)
Uncorrected distance visual acuity was measured using standardized logMAR charts.
Time frame: 1 week, 1 month, 3 months, 6 months, and 12 months postoperatively
Corrected Distance Visual Acuity (CDVA)
Corrected distance visual acuity was assessed to evaluate visual safety after surgery.
Time frame: 1 month, 3 months, 6 months, and 12 months postoperatively
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Allocation
NA
Purpose
TREATMENT
Masking
NONE
Enrollment
113
Surgically Induced Astigmatism (SIA)
Surgically induced astigmatism, expressed in diopters (D), represents the vector magnitude of astigmatic change produced by surgery. It was calculated using the Alpins vector analysis method by comparing preoperative and postoperative refractive cylinder magnitude and axis.
Time frame: 3 months and 12 months postoperatively
Target Induced Astigmatism (TIA)
Target induced astigmatism, expressed in diopters (D), represents the vector magnitude of astigmatic correction intended by the surgical plan. It was calculated using the Alpins vector analysis method based on the preoperative refractive cylinder magnitude and the planned axis of correction.
Time frame: 3 months and 12 months postoperatively
Difference Vector (DV)
Difference vector (DV), expressed in diopters (D), represents the vector magnitude of residual astigmatism that would need to be corrected to achieve the intended target. It was calculated using the Alpins vector analysis method based on postoperative refractive cylinder magnitude and axis relative to the planned correction.
Time frame: 3 months and 12 months postoperatively
Correction Index (CI)
Correction index, expressed as a unitless ratio, represents the ratio of surgically induced astigmatism to target induced astigmatism. It was calculated using the Alpins vector analysis method to quantify the accuracy of astigmatic correction. A value of 1.0 indicates exact correction, values greater than 1.0 indicate overcorrection, and values less than 1.0 indicate undercorrection.
Time frame: 3 months and 12 months postoperatively
Angle of Error (AE)
Angle of error, expressed in degrees (°), represents the angular difference between the achieved astigmatic correction and the intended target axis. It was calculated using the Alpins vector analysis method based on the deviation between the axis of surgically induced astigmatism and the planned treatment axis. Positive and negative values indicate counterclockwise and clockwise deviations from the intended axis, respectively.
Time frame: 3 months and 12 months postoperatively
Higher-Order Aberrations
Ocular higher-order aberrations were measured using wavefront aberrometry to assess postoperative visual quality.
Time frame: 1 week, 1 month, 3 months, 6 months, and 12 months postoperatively.
Contrast Sensitivity
Contrast sensitivity was evaluated under photopic conditions to assess functional visual quality.
Time frame: 1 week, 1 month, 3 months, 6 months, and 12 months postoperatively
Lenticule Decentration
Lenticule decentration is defined as the linear displacement between the intended lenticule center and the corneal vertex during SMILE PRO surgery. This parameter is automatically recorded intraoperatively by the CentraLign software integrated into the VisuMax 800 femtosecond laser system, based on real-time centration alignment guidance. Decentration is quantified as a continuous variable and expressed in millimeters (mm). For descriptive analysis, decentration values are categorized as \< 0.1 mm, 0.1-0.19 mm, and ≥ 0.2 mm. For regression analyses, the continuous decentration value (mm) is used.
Time frame: Intraoperative
Intraoperative Cyclotorsion
Intraoperative cyclotorsion is defined as the rotational misalignment (in degrees) between the preoperative reference axis obtained from iris registration and the intraoperative axis detected during docking using the OcuLign and CentraLign systems integrated into the VisuMax 800 platform. Cyclotorsion is recorded automatically by the system in degrees (°). Negative values indicate clockwise rotation and positive values indicate counterclockwise rotation. The magnitude of cyclotorsion is analyzed in relation to postoperative refractive outcomes.
Time frame: Intraoperative