SMILE Applicable Even in High Myopic Astigmatism

Small-incision lenticule extraction (SMILE) surgery is effective, safe, and predictable for myopic astigmatism of 2.00 D or more, according to research published in BMC Ophthalmology.

Although there have been concerns about SMILE’s effectiveness in correcting astigmatism, a few studies have indicated that the surgery can be successful. The researchers decided to investigate the safety, effectiveness, predictability, and influencing factors of SMILE for high myopic astigmatism.

Thirty-seven adult patients (55 eyes) underwent SMILE surgery for correcting myopia (sphere measurement of <10.00 D) and myopic astigmatism (cylinder measurement of ≥2.00 D) between April 2017 and May 2019 in China. Astigmatism correction was evaluated based on Alpins formulas and definitions. 

The sphere was overcorrected by approximately 10%, and the cylinder was precisely corrected. Patients were prescribed levofloxacin eye drops 3 days preoperatively and hormone eye drops postoperatively.

The surgery was successful for correcting myopia and myopia astigmatism in all eyes, without intraoperative or postoperative complications. Uncorrected visual acuity (UCVA) improved postoperatively in all patients; at 3 months after surgery, 48 eyes had UCVA of 20/20 or better and spherical equivalent (SE) within approximately 0.50 D. All eyes at 3 months after surgery had UCVA of 20/25 or better. The median efficacy index at 2 days, 1 month, and 3 months after surgery was 0.67, 0.80, and 0.83, respectively.

In terms of predictability, the mean SE was -0.14 D (SD 0.35 D range, -0.75 D to +0.50 D) and -0.15 (SD 0.36 D, range, -0.75 D to +0.50 D) at 1 and 3 months after surgery, respectively. The mean cylinder was -0.15 (SD, 0.33 D, range, -1.00 D to +0.50 D) at 1 month postoperatively and -0.14 (SD 0.31 D, range, -1.00 D to +0.75 D) at 3 months postoperatively, respectively. Target-induced astigmatism (|TIA|) and surgically induced astigmatism vector (|SIA|) had significant association at 1 month and 3 months after surgery (r=0.947 and 0.914, respectively).

At 3 months postoperatively, the correction index (CI) was 0.98 (± 0.07), the index of success (IOS) was 0.08 (± 0.13), the flattening index (FI) was 0.97 (± 0.07), mean astigmatism vector was -0.09 D × 6.34°, angle of error (AofE) was limited to within approximately 10°, and magnitude of error was limited to within approximately 1.0 D. 

All eyes also had both SE and postoperative cylinder of approximately 1.0 D at 3 months. Total higher order aberration (T-HOA), spherical aberrations, vertical coma aberration, and trefoil 30° had significantly increased compared with preoperative measurements (P <.05).

The increase in HOA was closely related to preoperative astigmatism. Significant positive correlations were found between IOS and |AofE|, while negative correlations were found between FI and AofE (P for each comparison =.000).

The researchers recommended surgeons accurately center the visual axis when using SMILE to correct high myopic astigmatism and adjust nomograms or use manual compensation for rotation errors.

Limitations of the study included the relatively short observation and the likelihood that variance between eyes of bilaterally treated patients may result in an increased risk of type 1 error.

Reference

Hou X, Du K, Wen D, et al. Early visual quality outcomes after small-incision lenticule extraction surgery for correcting high myopic astigmatism. BMC Ophthalmol. Published online January 19, 2021. doi:10.1186/s12886-021-01807-8