Changes in Intraocular Pressure and Factors that Influence such Changes after FS-LASIK and SMILE

Purpose: We compared the intraocular pressure (IOP) changes and the relationships thereof with corneal biomechanics after small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK). Methods: A total of 234 eyes of 117 patients who underwent FS-LASIK surgery and 244 eyes of 122 patients who underwent SMILE surgery were included in this retrospective study. Data were collected preoperatively, and at 1, 3, and 6 months post-operatively, including IOP measured via non-contract tonometry, central corneal thickness (CCT), and mean keratometry (Km), flat keratometry (Kf), and steep keratometry (Ks) data obtained using a dual Scheimpflug analyzer. Between-group differences were compared. Simple linear regression analysis was used to determine the relationship between changes in the IOP and the various parameters. Results: The IOP changes were 5.41 +/- 2.28 mmHg in the FS-LASIK group and 4.77 +/- 2.38 mmHg in the SMILE group, thus significantly different (p = 0.004). The IOP did not change significantly from 1 to 6 months after FS-LASIK but increased significantly from 12.07 +/- 1.77 mmHg at 3 months postoperatively to 12.77 +/- 1.89 mmHg at 6 months postoperatively after SMILE (p = 0.002). All of the preoperative spherical equivalent and IOP, and changes in the Km, Kf, Ks, and CCT, were significantly associated with the IOP changes in both groups. The preoperative IOP evidenced the strongest relationship with the IOP changes in both groups (R-2 = 0.414 in the FS-LASIK group, R-2 = 0.292 in the SMILE group). Conclusions: The IOP fell significantly after FS-LASIK and SMILE surgery, significantly more so after FS-LASIK than SMILE. The preoperative IOP exhibited the greatest influence on the IOP decreases after both FS-LASIK and SMILE.