Evaluation Of Angle Kappa In Patients Undergoing Smile For Myopia

The decentration of ablation zone in patients of large angle kappa undergoing laser refractive surgery can lead to under-correction and irregular astigmatism while in patients undergoing implantation of multifocal or trifocal intraocular lenses can lead to underwhelming visual outcomes and increased photic phenomenon. The angle kappa has been shown to change following LVC, though the effect has not been studied widely in patients undergoing SMILE. Orbscan IIz is a widely used corneal topographer in measurements during LVC. The topographer is also a reliable method to estimate angle kappa This study aims to evaluate the changes in angle kappa in patients of myopia undergoing SMILE utilizing Orbscan IIz.

A single centre prospective trial to observe changes following SMILE for a follow-up period of 3 months to study the changes in posterior corneal curvature in participants undergoing SMILE for myopia.

Minimum sample size was 225 eyes and with the institutional drop-out rate of follow-up taken into account, 280 eyes were recruited in the study. All the participants underwent preoperative evaluation and routine corneal topography with Orbscan IIz. A standard operative protocol for SMILE was maintained throughout the study period. The corneal topography with Orbscan IIz was done at 1-week, 1-month and 3-month follow-up. The changes in angle kappa were assessed. Shapiro-Wilk test for the normalcy of data while paired t-test for comparing preoperative and postoperative changes in angle kappa changes were employed.

In 131 eyes, the angle kappa increased significantly (4.75±1.1° to 5.24±1.2°) while in 117 eyes it decreased significantly (5.02±1.4° to 4.52±1.4°). The increase in angle kappa had a significant negative correlation with lenticule thickness (Coefficient= -0.308, p<0.01) and simulated keratometry readings (coefficient=-0.186, p=0.33). The decrease in angle kappa though showed a significant positive correlation with pachymetry (coefficient = 0.277, p=0.03).

The study indicates that angle kappa does change significantly following SMILE, and the effect of this change needs to be studied more robustly to provide a better visual outcome later in life, when the patients undergoing SMILE will need cataract surgery and IOL implantation.