The results from this retrospective, non-blind, case-series clinical study demonstrated that all corneal refractive surgery produced excellent visual and refractive outcomes in terms of refractive efficacy and safety. Nonetheless, our results suggest that all corneal refractive procedures had similar visual outcomes after surgery. In the analysis of UDVA and CDVA changes, a preoperative CDVA of 20/20 or better was seen in 100%, 100%, and 90% of eyes in SMILE, T-PRK, and FS-LASIK, respectively. Moreover, in terms of the difference between postoperative UDVA and preoperative CDVA, 57% of the eyes showed no changes, 22% of the eyes showed a gain one or more lines, 18% of eyes showed a loss one line.
Previously, Tobaigy et al. [21] and Scerrati et al. [22] suggested that the visual and refractive outcomes were better in surface ablation than stromal ablation. However, Kim et al. [23] reported that corneal stromal ablation surgery was superior to corneal surface surgery for high myopia. A longitudinal follow-up study concluded that corneal surface and stromal ablation surgery had similar efficacies for moderate myopia within 2 years, with a significantly superior efficacy in corneal surface ablation surgery after 4 years postoperatively. Meanwhile, the corneal stromal ablation surgery showed greater myopic regression 5 years postoperatively [24]. According to the current short-term follow-up results, there were superior outcomes in the early stage of corneal stromal ablation surgery and corneal lenticule extraction procedures than corneal surface ablation technique. Moreover, there were no statistically significant difference in efficacies within all procedures.
For this retrospective clinical study, we used the AKP analysis method [20] to evaluate the astigmatism changes after surgery, and found that according to this algorithm, corneal ablation was not significantly different within all procedures during the 6-month postoperative period. However, there was a statistically significant difference in AKP(+ 0) preoperatively. It means that corneal refractive surgery corrects the refraction error with changes to the corneal biomechanical properties by using the bitoric LASIK technique with an aspheric profile to create a smooth transitional zone between the treated and untreated cornea [25–27]. This ablation technique was achieved by balancing the negative and positive cylinder ablations, creating a more aspheric optical zone. Moreover, the optimized centration in the SMILE procedures between the corneal vertex and optical zone center [28] were analyzed, and it was found that there was no significant difference in centration between SMILE and LASIK procedures [29].
There were also no major intraoperative or postoperative complications reported during the study period. Flumetholon was applied for the patients with minor postoperative symptoms such as visual fluctuation and dry eye which were temporary (resolved during 3 months postoperatively) and not significantly different in terms of their occurrence between all eyes included in this clinical study [30]. Of note, the efficacy, predictability, and safety outcomes of all procedures in the current case-series study after 6 months postoperatively were comparable with previously reported studies [17, 31].
We recognize that this retrospective clinical study has some limitations. This was a short-term follow-up study in which there was myopic regression after corneal refractive surgery for 10-year follow-up in a previous study [24]. Second, there was no evaluation of the visual quality (which may include increased occurrence of symptoms such as halos, glare, and starbursts) within groups. However, we noted that patients reported more uncomfortable symptom (such as fluctuation in vision) in SMILE or T-PRK treated eyes than in FS-LASIK-treated eyes at 1 and 3 months after surgery. However, these symptoms reportedly diminished, and there was no difference between the eyes by 6 months. These results are important when counseling patients before surgery and explaining what to expect after the procedure, factors that sometimes are more pertinent to the patient than scientific results. Finally, there were no statistically significant differences in refractive outcomes or efficacy after surgery in the early postsurgical period. On the contrary, the postoperative outcomes were significantly better for the corneal stromal ablation than the corneal surface ablation technique [23], and superior refractive outcomes were obtained in SMILE procedures which is a more surgeon-dependent surgical technique. Further understanding of the ablation algorithms of the femtosecond and excimer lasers with more advanced clinical trial studies to improve postoperative visual and refractive outcomes are needed.