Experimental study on keratocyte apoptosis following Epi-LASIK and off-flap Epi-LASIK in rabbits

Background Epipolis laser in situ keratomileusis(Epi-LASIK)is a new surface ablation procedure that is proved to be a safe,efficient and predictable for the treatment of myopia.Epi-LASIK is a major advancement over PRK and LASEK.Some surgeons thought that the epithelial flap should be removed after excimer laser ablation to reduce the development of corneal haze and postoperative pain.The theoretical advantages of 'flap on' and 'flap off' techniques of Epi-LASIK have not yet been studied.ObjectiveThis study was to investigate the effects of Epi-LASIK and off-flap epipolis laser in situ keratomileusis(off-flap Epi-LASIK)on the keratocyte apoptosis.MethodsEpi-LASIK was performed in the lateral eyes and off-flap Epi-LASIK was performed in the fellow eyes in 40 New Zealand white rabbits,and 4 normal eyes of 2 rabbits were used as controls.The corneal specimen was prepared at 4 hours and 1 day,3,7 days after operation.Morphological change of the cornea was observed by transmission electron microscope.Apoptosis of cornea stromal cell was detected by terminal deoxyribonucleotidyl transferase-mediated deoxynuridine triphosphate nick end labeling(TUNEL)assay,and the expression of interleukin-1β(IL-1β)in the corneal stroma was assessed by immunocytochemistry.ResultsThe number of TUNEL-positive cells was higher in Epi-LASIK group than that in off-flap Epi-LASIK group,showing statistically significant differences between them(t=2.42,P0.05;t=4.04,P0.05).The expression level of IL-1β was enhanced in Epi-LASIK group in comparison with off-flap Epi-LASIK group at 1 day,3 and 7 days after surgery,and the differences presented the statistical significances(t=2.13,P0.05;t=3.71,P0.05;t=3.06,P0.05).Karyopyknosis,chromatin margination and apoptosis bodies were seen in corneal stroma after Epi-LASIK under the transmission microscope.Immunochemistry revealed that IL-1β expression in corneal stroma was stronger after Epi-LASIK in comparison with off-flap Epi-LASIK.ConclusionOff-flap Epi-LASIK has less damage to corneal stomal cells in comparison with Epi-LASIK,and therefore the repair process of corneal wound is more quickly.