The Ultrastructure and Apoptosis of Preserved SMILE-derived Corneal Stromal Lenticules Under Different Preservation Conditions

PURPOSE: To investigate the ultrastructure and apoptosis of small incision lenticule extraction (SMILE) lenticules under different preservation conditions. METHODS: A total of 104 corneal stromal lenticules of 52 patients (13 men and 39 women, age 28.85 ± 6.45 years, mean spherical error -4.27 ± 1.34 diopters [D]) were collected from small incision lenticule extraction (SMILE) surgeries, and were immediately preserved using glycerol, silicone oil, Optisol (Bausch & Lomb), and cryopreservation for 1 day, 1 week, and 1 month. Fresh lenticules were taken as control groups. Hematoxylin-eosin (HE) staining and transmission electron microscopy (TEM) were applied for evaluation of ultrastructure and terminal-deoxynucleoitidyl transferase mediated nick end labeling (TUNEL) for cell apoptosis ratio. Changes of quantity of collagen in TEM were evaluated in each group among all time points. RESULTS: HE staining showed that collagen in the fresh lenticules had an orderly arrangement with few vacuoles. In each preservation group, vacuoles and changes in arrangement of collagen were observed. TEM showed that the mean density of collagen was lowest at 1 month in the glycerol, silicone oil, and cryopreservation groups and highest at 1 month in the Optisol group. Quantities of collagen of lenticules preserved for 1 day and 1 week in the Optisol group were not statistically significantly different from those in the fresh group. At the same storage time, the mean density of collagen was the highest in the cryopreservation group at 1 day and the Optisol group at 1 month, and there was no statistically significant difference among the other groups. There was no statistically significant difference in apoptotic cell ratio among groups. CONCLUSIONS: SMILE lenticules preserved using glycerol, silicone oil, Optisol, and cryopreservation within 1 month maintain a similar cell viability level as fresh lenticules.