Effects of Laser In Situ Keratomileusis and Small-Incision Lenticule Extraction on Corneal Biomechanical Behavior: A Finite Element Analysis

Corneal Epithelial Remodeling in a 6-Month Follow-up Period in Myopic Corneal Refractive Surgeries

PURPOSE

To investigate corneal epithelial thickness changes during a 6-month follow-up period after transepithelial photorefractive keratectomy (tPRK), femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK), and small incision lenticule extraction (SMILE).

METHODS

This prospective study included 76 eyes of 76 participants who underwent myopic refractive surgery (23 FS-LASIK, 22 SMILE, and 31 tPRK). Epithelial thickness and anterior curvature were averaged over 4 regions (subdivided into 25 areas) and measured by spectral-domain optical coherence tomography and Scheimpflug tomography before the operation (pre) and at 1 or 3 days (pos1-3d), 1 week (pos1w), and 1 month (pos1m), 3 months (pos3m), and 6 months (pos6m) postoperatively.

RESULTS

The epithelial thickness of the three groups was similar in both the pre and pos6m (all P > .05), but the tPRK group fluctuated the most during the follow-up period. The largest increase was in the inferior-temporal paracentral area (7.25 ± 2.58 μm for FS-LASIK; 5.79 ± 2.41 μm for SMILE; 4.88 ± 5.84 μm for tPRK; all P < .001). Only the epithelial thickness of tPRK increased from pos3m to pos6m (P < .05), whereas all changes for FS-LASIK and SMILE were not significant (P > .05). A positive correlation of thickness changes with curvature gradient in the paracentral region of tPRK was found (r = 0.549, P = .018), but not in other regions in all groups.

CONCLUSIONS

Epithelial remodeling followed different trends after different surgeries from the early postoperative stage onward, but exhibited similar values at pos6m. Although remodeling after FS-LASIK and SMILE stabilized by pos3m, it remained unstable at pos6m after tPRK. These changes may affect corneal profile and lead to deviation from the intended surgical outcome. [J Refract Surg. 2023;39(3):187-196.].

Predictive models for IOPs measured with NCT, GAT, and ORA among patients undergoing SMILE

Purpose: To develop predictive models for the intraocular pressure (IOP) of patients undergoing small incision lenticule extraction (SMILE) procedures, measured with a noncontact tonometer (NCT), Goldmann applanation tonometry (GAT), and an ocular response analyzer (ORA). Methods: In this prospective study, a total of 104 eyes (-6.23 ± 2.06 diopters) of 52 patients (24.38 ± 4.76 years) undergoing SMILE procedures were included. The intraocular pressure was measured (IOPNCT with NCT, IOPGAT with GAT, and IOPcc and IOPg with ORA) before surgery and at postoperative 6 months. Information on age, preoperative and attempted spherical equivalent (SE), ablation depth, preoperative values and postoperative changes in central corneal thickness (CCT), K1, K2, Km, corneal hysteresis (CH) and corneal resistance factor (CRF) values was collected in order to predict IOPs. Results: All surgeries were uneventful. At postoperative 6 months, the efficacy and safety index were 1.04 ± 0.15 and 1.08 ± 0.18, respectively. Significant decreases were detected in postoperative IOPNCT, IOPGAT, IOPcc, and IOPg compared to preoperative values (all p < 0.001). No relationship was found between any IOP and ablation depth, attempted SE, and preoperative SE, as well as CCTdifference (all p > 0.05). Predictive models for IOPs were constructed to predict preoperative values, and R 2 values were 67.5% (IOPNCT), 64.5% (IOPGAT), 78.7% (IOPcc), and 82.0% (IOPg). The prediction band of IOPNCT and IOPGAT was 7.4-15.1 mmHg and 8-16 mmHg, respectively. Conclusion: Predictive models for IOP measurements after SMILE procedures can be helpful in clinical practice.

Comparison of the biomechanical differences in the occlusal movement of wild-type and BMP9 knockout mice with apical periodontitis

Apical periodontitis is a common clinical disease caused by bacteria; bacterial metabolites can cause an imbalance in bone homeostasis, bone mass reduction, and tooth loss. Bone resorption in apical periodontitis causes a concentration of stress in the tooth and periodontal tissues during occlusion, which aggravates the disease. Emerging evidence indicates that bone morphogenetic protein 9 (BMP9), also known as growth differentiation factor 2(Gdf2), may play an important role in tooth and dentoalveolar development. Herein, we investigated the role of BMP9 in the development of apical periodontitis and its effects on the biomechanics of dentoalveolar bone. Apical periodontitis models were established in five BMP9 knockout (KO) mice and five C57BL/6 WT (wild-type) mice. At baseline and 14, 28, and 42 days after modeling, in vivo micro-computed tomography analysis and three-dimensional (3D) reconstruction were performed to evaluate the apical lesion in each mouse, and confirm that the animal models were successfully established. Finite element analysis (FEA) was performed to study the stress and strain at the alveolar fossa of each mouse under the same vertical and lateral stress. FEA revealed that the stress and strain at the alveolar fossa of each mouse gradually concentrated on the tooth cervix. The stress and strain at the tooth cervix gradually increased with time but were decreased at day 42. Under the same lingual loading, the maximum differences of the stress and strain at the tooth root in KO mice were greater than those in WT mice. Thus, these findings demonstrate that BMP9 could affect the biomechanical response of the alveolar fossa at the tooth root in mice with apical periodontitis. Moreover, the effects of BMP9 on the biomechanical response of the alveolar bone may be site-dependent. Overall, this work contributes to an improved understanding of the pathogenesis of apical periodontitis and may inform the development of new treatment strategies for apical periodontitis.