Histochemical and ultrastructural evaluation of myopic corneal lenticules based on refractive error

This study aimed to investigate cell degeneration, apoptosis, and ultrastructural differences in refractive lenticules (RL) obtained using small incision lenticule extraction (SMILE) compared with spherical equivalence (SE) refraction values.

This study included 84 eyes from 42 patients. Patients were divided into two groups according to the SE values: those with values below 4 diopters (D) (Group 1) and above 4 diopters (D) (Group 2). Patients who did not belong to the same SE group were excluded from the study. One RL obtained from each patient was separated for light microscopy and immunohistochemical examinations, and another for transmission electron microscopy (TEM) examinations. Caspase-3 for apoptosis and alpha-smooth muscle actin (α-SMA) for cell degeneration were evaluated using immunohistochemical examinations.

Histological analyses showed that the density of collagen fibres was greater in Group 1 than in Group 2. Glycoaminoglycan and glycoprotein staining intensities were also higher in Group 1. TEM observations showed that Group 1 had intact cell and nuclear membranes, peripheral heterochromatin, and large nuclei, while Group 2 showed heterochromatin condensation and fragmentation, increased intracellular vacuoles, and loss of cytoplasm. Immunohistochemical analyses revealed that α-SMA and caspase-3 were significantly higher in Group 2 than in Group 1 (p < 0.001 and p < 0.001, respectively).

Cell degeneration and apoptosis were significantly more common in the RLs with high SE values after SMILE surgery. The tissue response induced by surgery was more severe in the RLs with high SE values. This should be considered when reusing RLs.