Effects of small incision lenticule extraction and femtosecond laser‑assisted <i>in situ</i> keratomileusis on choroidal thickness and blood flow density in patients with myopia

Corneal refractive surgery is often used to correct myopia, and after surgery attention is often focused on changes in vision and corneal response. However, studies on the posterior segment of the eye remain relatively scarce. The present study aimed to observe changes in choroidal thickness and blood flow density after small incision lenticule extraction (SMILE) and femtosecond laser-assisted <i>in situ</i> keratomileusis (FS-LASIK) using optical coherence tomography. Changes in spherical equivalent (SE), axial length (AL), choroidal thickness and choriocapillaris blood flow density were recorded before and after surgery in 35 patients (70 eyes) who underwent SMILE and 21 patients (42 eyes) who underwent FS-LASIK. Postoperative SE significantly improved in both groups (P<0.05), and AL was shorter than the baseline level (P<0.05). Choroidal thickness initially increased and subsequently decreased to preoperative levels at multiple measurement sites in both groups. No significant changes were observed in choriocapillaris blood flow density in the two groups postoperatively compared with preoperatively. In conclusion, the results indicated that SMILE and FS-LASIK exert minimal influence on the choroid. To the best of our knowledge, the current study presents one of the first comparative assessments of dynamic choroidal changes following SMILE and FS-LASIK, offering insights into structural alterations in the posterior segment post-surgery.