Ultrastructural and Immunohistochemical Characteristics of Corneal Lenticule Extracted during Correction of Residual Myopia in the Long-Term Period after SMILE

Purpose: To evaluate ultrastructural characteristics of lenticule surface extracted during correction of residual myopia in patients after small-incision lenticule extraction (SMILE). Methods and material: This study had a prospective, consecutive, comparative design. Sixteen patients (16 eyes) underwent additional intervention for residual myopia correction after SMILE. 16 specimens of removed lenticules underwent morphological examination. Markers and reagents were used to determine actin microfilaments, neutral fats and cell nuclei. The tissue was analyzed in layers in 2D slices form, volumetric Z-stacks, or selected areas were formed in orthogonal projections. The surface of the extracted lenticule was analyzed using scanning electron microscopy. Patients’ refractive outcomes were measured postoperatively (1 day;1 and 3 months). Results: Postoperatively uncorrected distance visual acuity (20/20 or better) was in 100% cases 3 months after surgery. Ultrastructural studies have shown the difference in surfaces of the newly formed lenticule. Structural changes of the posterior lenticule surface were characterized by ruptures of collagen fibers on its surface, degenerative changes in keratocytes with signs of colliquation necrosis, cell apoptosis and F-actin in cell cytoplasm. Conclusion: Collagen fibers are immersed in the stroma on the anterior surface of the lenticule. There is no complete structure restoration of collagen fibers explaining the lack of tight adhesion of anterior and posterior surfaces of the intrastromal space even in the long-term postoperative period. There are no degenerative changes of keratocytes on the anterior lenticule surface, that is, their changes in SMILE are reversible in most cases.