Clinical Outcomes of Small-incision Lenticule Extraction (SMILE) Using Vector Planning Method.
Condition: Myopic Astigmatism
MeSH terms: Astigmatism
Study type: Interventional

Summary: 
      In the past two decades, the femtosecond laser (FSL) technology has been introduced in the
      corneal refractive surgery filed, and brought a remarkable innovation. It can make tissue
      dissection through photodisruption and plasma cavitation. Initially, the FSL was used
      predominantly to make a corneal flap when performing laser in situ keratomileusis (LASIK),
      which is followed by stromal ablation using excimer laser. A new surgical technique called
      femtosecond lenticule extraction (FLEx) has been developed that uses only FSL to dissect two
      interfaces to create refractive lenticule and then remove it, which is very similar with
      LASIK. Small incision lenticule extraction (SMILE) which is the advanced form of all-in-one
      FSL refractive technique does not make a corneal flap rather make small incision where the
      separated refractive lenticule is removed through, and the upper part of the corneal tissue
      is called cap. Since the clinical outcomes of SMILE were firstly published in 2011, SMILE has
      been widely used for correction of myopia or myopic astigmatism worldwide. SMILE provides
      excellent visual outcomes and has advantages including a lesser decrease in corneal
      sensitivity and absence of flap related complications compared to LASIK.

      The vector planning method is newly developed astigmatism correction method, which combines
      refraction astigmatism in 60 % emphasis and corneal astigmatism in 40 % emphasis. The
      vectorial difference between corneal astigmatism and refractive cylinder at the corneal plane
      is ocular residual astigmatism (ORA). In normal eyes treated for myopic astigmatism, the ORA
      typically ranges from 0.73 to 0.81 D. The eyes with high ORA resulted in inferior clinical
      outcomes after corneal refractive surgery including LASIK, LASEK, and SMILE. The vector
      planning method was effective in LASIK according to previous study. Therefore we try to
      confirm the efficacy of vector planning method in SMILE.
    

Detailed description: 
      Enrollment period : 6 months after IRB approval Participants : The subjects over 20 years
      old, who visited Severance hospital and Eyereum eye clinic for SMILE surgery with myopic
      astigmatism. The participants who satisfies criteria, and who can be monitored at all times
      during each period of observation after surgery are included in the study.

      Methods: The subjects are randomly divided into two groups. One group underwent SMILE surgery
      using manifest refraction based planning, and the other group underwent SMILE surgery using
      vector planning. Before surgery, all patients underwent a detailed ophthalmological
      examination that included evaluation of logarithm of the minimum angle of resolution (logMAR)
      uncorrected-distance visual acuity (UDVA) and CDVA, manifest refraction, slit-lamp
      examination (Haag-Streit, Köniz, Switzerland), keratometry, and Scheimpflug-based corneal
      topography (Pentacam HR, Oculus). Dynamic corneal response (DCR) parameters were examined
      using Corvis ST. Corneal wavefront aberrations were measured using Keratron Scout (Optikon
      2000, Rome, Italy). All examinations were repeated at 1, 3, and 6 months after surgery.
    

Intervention name(s): SMILE using manifest refraction planning; SMILE using vector planning
Intervention type(s): Procedure; Procedure
Intervention description(s): The treatments of astigmatism were planned using either the manifest refraction (manifest refraction group) or the vector planning method (vector planning group). The surgery was performed with standardized techniques with triple centration technique using the 500-KHz VisuMax system (Carl Zeiss Meditec AG, Jena, Germany). The superior cap depth was set as 120 µm, and the length of the side cut was set to 2 mm. Once the anterior (upper) and posterior (lower) planes of the lenticule were defined, the anterior and posterior interfaces were dissected using a microspatula with a blunt circular tip and extracted with microforceps. The integrity of the lenticule was assessed subsequently. The treatment plan for the vector planning group involved a combination of refractive astigmatism with 60 % emphasis and corneal astigmatism with 40 % emphasis.; The treatments of astigmatism were planned using either the manifest refraction (manifest refraction group) or the vector planning method (vector planning group). The surgery was performed with standardized techniques with triple centration technique using the 500-KHz VisuMax system (Carl Zeiss Meditec AG, Jena, Germany). The superior cap depth was set as 120 µm, and the length of the side cut was set to 2 mm. Once the anterior (upper) and posterior (lower) planes of the lenticule were defined, the anterior and posterior interfaces were dissected using a microspatula with a blunt circular tip and extracted with microforceps. The integrity of the lenticule was assessed subsequently. The treatment plan for the vector planning group involved a combination of refractive astigmatism with 60 % emphasis and corneal astigmatism with 40 % emphasis.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Small incision lenticule extraction; astigmatism; vector planning