[The structure and viability analysis of corneal epithelial flap in the rabbit cornea after Epi-LASIK]

To evaluate the changes of ultrastructure and viability in the rabbit corneal epithelial flap after Epi-LASIK (epiploic laser in-situ keratomileusis) surgery and its effect on keratocyte apoptosis and proliferation of peripheral corneal epithelium (out of corneal epithelial flap).

Fifty-eighty eyes of 29 New Zealand rabbits were used, Epi-LASIK was performed in 28 eyes and Photorefractive keratectomy (PRK) was carried out in 24 eyes. treated-eyes were randomly divided into four groups and were sacrificed at 1, 3, 5, 7 days after surgery, six eyes without treatment were served as blank controls. Histological structure from The specimens of Epi-LASIK and controls eyes were assessed by light, transmission electron microscopy; epithelial cells viability were assessed by enzyme-histochemistry and Immunohistochemistry staining (proliferating cell nuclear antigen, PCNA) were performed to detect proliferation of peripheral corneal epithelial cells. Apoptotic cells were detected by TUNEL assay (TdT-mediated dUTP nick-end labeling) from the specimens of Epi-LASIK and PRK.

The study from Transmission electron microscopy demonstrated that epithelial flap separated by KM5000D type epikeratome retained its typical stratification and integrity and the basement membrane including lamina densa and lamina lucida were compaginated with stroma. The expression of ATP enzyme, G-6-P enzyme from epithelial flap to peripheral epithelium of Epi-LASIK-treated eyes were (79%, 58%, 69%, 86%), (79%, 63%, 77%, 97%) at 1, 3, 5, 7 days after surgery respectively. There was no statistically significant difference in the cell Viability and the number of PCNA in peripheral epithelial cells among four Epi-LASIK groups and control group. At 1 day after surgery, no difference in TUNEL positive cells were seen between specimens of Epi-LASIK (3.429 +/- 1.693) and PRK (3.796 +/- 1.998); At 3, 5, 7 days, there was a significant difference in the number of keratocyte apoptosis in PRK compared to Epi-LASIK specimens.

Epithelial flap separated by KM5000D type epikeratome retained its typical stratification and integrity. The flap keeps high viability and no peripheral epithelial cell proliferation and therefore it may play a role in the inhibition of keratocyte apoptosis.