Hydroxyproline Concentration and Associated Factors of Preserved Small Incision Lenticule Extraction–Derived Corneal Stromal Lenticules

Purpose: To evaluate changes of hydroxyproline concentration and its influencing factors of small incision lenticule extraction (SMILE)-derived corneal stromal lenticules with different preservation methods. Methods: A total of 390 corneal stromal lenticules of 195 patients were derived from SMILE surgeries. Thirty of the lenticules were classified as the fresh (control) group, and the rest were randomly and evenly divided and stored in anhydrous glycerol, silicone oil, Optisol, and cryopreservation for 1 day, 1 week, or 1 month. A hydroxyproline assay kit (ab222941, Abcam) was used to measure the hydroxyproline concentration in each preservation method. Concentrations of MMP-2, TIMP-2, TNFα, TGFβ2, and reactive oxygen species were also evaluated. Results: In the anhydrous glycerol group, the concentration of hydroxyproline decreased within 1 week (fresh: 1 dΔ = 0.229, P < 0.001*; 1 d − 1 wΔ = 0.055, P < 0.001*) while that in the silicone oil group remained stable in 1 week (1 d − 1 wΔ = −0.005, P = 0.929) and decreased significantly in 1 m (1 m − 1 wΔ = −0.041, P = 0.003*). The sequence of hydroxyproline concentration in the Optisol group was 1 m > 1 day > 1 week. Hydroxyproline concentration in the cryopreservation group decreased within 1 m. Hydroxyproline concentration was highest in the Optisol group and lowest in the anhydrous glycerol group under the same preservation time. Hydroxyproline concentration was negatively correlated with MMP-2 (r = −0.16, P = 0.421) and TIMP-2 (r = −0.56, P = 0.002*) while MMP-2 and TNFα (r = 0.17, P = 0.242), TIMP-2 and TGFβ2 (r = 0.21, P = 0.207), and TNFα and reactive oxygen species (r = 0.52, P = 0.007*) were positively correlated. Conclusions: More collagen was retained in SMILE lenticules preserved in Optisol under the same preservation time. The mechanism of the changes of collagen in preserved SMILE-derived lenticules and oxidative stress requires additional investigation.