Intraocular Pressure Changes and Relationship With Corneal Biomechanics After SMILE and FS-LASIK.

PURPOSE: The purpose of this article was to evaluate intraocular pressure (IOP) changes and investigate the relationship with corneal biomechanics after small-incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK).

METHODS: A total of 193 eyes of 193 patients who underwent SMILE and FS-LASIK procedures were included in this retrospective study. Data were collected preoperatively and postoperatively, including Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF) by ocular response analyzer, noncontact intraocular pressure (IOPNCT) by noncontact tonometer, and Ehlers, Shah, Dresden, Kohlhaas, Orssengo/Pye by the Pentacam corrected system. Changes in both groups and differences between groups were evaluated. Multiple linear regression models were constructed to explore factors influencing IOP changes.

RESULTS: In SMILE, the IOPg, IOPcc, IOPNCT, and Kohlhaas decreased significantly at 1 month postoperatively (P < 0.01), whereas with the Ehlers formula they significantly increased (P < 0.01). IOPs decreased at 3 and 6 months compared with all preoperative values except Ehlers values (P < 0.01), but there was no significant difference between 3 and 6 months (P > 0.05). In FS-LASIK, the IOPg, IOPcc, and IOPNCT decreased significantly at 1 month (P < 0.01), whereas in the Ehlers and Shah formulas they significantly increased (P < 0.01). Compared with preoperative values, the IOPs decreased at 3 and 6 months except in the Ehlers and Shah formulas (P < 0.01). Only IOPg and IOPcc differed between 3 and 6 months (P < 0.05). The Ehlers and Shah formulas were closer to the preoperative IOP for both groups, with variation approximately 1 mm Hg at 6 months postoperatively. Preoperative IOP, postoperative corneal resistance factor, corneal hysteresis, and flat keratometry were enrolled into the regression equations.

CONCLUSIONS: IOP underestimation after SMILE or FS-LASIK was related to corneal biomechanics as well as preoperative IOP and flat keratometry. IOP after SMILE seem to remain more stable. Accordingly, the Ehlers and Shah formulas were closer to the preoperative IOP. It may be useful to estimate future IOP with the best-fit models after surgery.