Overview

Laser in situ keratomileusis (LASIK), a refractive surgery procedure, has been in vogue for over 2 decades for the correction of refractive error. The refractive error correction is achieved by the ablation of the required amount of corneal stromal tissue by an excimer laser.

TheWaveLight®EX500 excimer laser system is the most recent Alcon excimerlaser. Treatment planning for LASIK is done with the refractive error correction data and with orwithout other patient specific pre-surgical data. Wavefront guided or Wavefront optimized has been the main method of laser refractive correction. In recent years interest in Topography Guided LASIK has developed as a modality of treatment and has been used primarily for the treatment of irregular ordiseased corneas that either had never been treated or had been previously treated

More recently, Topography Guided LASIK is being used as a primary treatment for regular corneas. A study by Stultinget. al showed thatTopography Guided LASIK as a primary treatment for myopia with or without astigmatismwas safe and effective in subjects who had regular corneas (Stulting 2016). The advantage that a topography guided treatment has over wavefront treatment is that it has more static and reproducible data with collection of more data points from the peripheral cornea thereby enabling the creation of a smoother and more customized ablation profile.

Small incision lenticular extraction (SMILE) is the newest refractive surgery procedure thatis being used for the correction of myopia with or without astigmatism. The Zeiss VisuMaxsurgical laser, a femtosecond laser, is the only marketed laser for the SMILE procedure. The VisuMax creates a lenticule of corneal tissue and a small (<4mm)channel through which the lenticule is removed. The removal of the lenticule results incorrection of the refractive error.

Fundamental difference between the EX500 and VisuMax are that the EX500 provides centration and cyclotorsion control, and the VisuMax does not. Centration and cyclotorsioncontrol allow for better correction of astigmatism. Additionally, use of the topography datafor treatment planning of Topography Guided data should allow for better correction ofastigmatism compared to SMILE for which topography data is not used for treatmentplanning.

HYPOTHESIS

This study is designed to test the differences in astigmatism treatment between TopographyGuided LASIK and SMILE. The difference in astigmatism treatment between the two refractive surgeries is hypothesized to be related to the differences in the lasers and treatment planning.

With Topography Guided LASIK, the cyclotorsion control and the centrationfeatures of the EX500 laser and the use of topography data for treatment planning should enhance the accuracy of astigmatism treatment. In contrast, with SMILE, the VisuMaxLaserkeratome does not have cyclotorsion control or centration nor is topography data used for treatment planning.

This contralateral eye study performed in eyes with astigmatism >1D would enable an effective comparison of the efficacy of the two techniques in correction of astigmatism. 

Purpose: The purpose of the study is to compare the visual outcomes of Topoguided Lasik with SMILE performed in contralateral eyes with Myopic astigmatism.

Material & Methods:

Eyes which meet the inclusion criteria to undergo baseline screening procedures including cycloplegicrefracton, Pentacam Tomography, Aberrometry, Pupillometry, Dry Eye Work up & Axial length measurements, Corneal Biomechanics measurements using Corvis  within a period of 1 month from the procedure.

The patients will be randomized to undergo topoguided LASIK in one eye & SMILE in the contralateral eye. All patients will undergo bilateral treatment for contralateral eye comparison.

Follow up visits: Day 1, 1 week, 1 month, 3 months & 1 year.

Outcome Parameters:

1.Primary: Percentage of eyes with residual cylinder >0.5D at 3 months.

Secondary:

1.Percentage of eyes with atleast 1 line gain in BCVA at 3 months

2.Percentage of eyes with UCVA of 20/20 or better at 3 months

3. To evaluate Induction of Higher Order Aberrations post procedure

4. To assess Quality of Vision & Vision related Quality of life through Questionnaire post procedure