| PurposeThe excimer laser revolutionized the world of refractive surgery in the1990s. Laser in situ keratomileusis (LASIK) is that the excimer laser treatment is performed under a corneal flap. As in all surgery, there are risks and potential complications. Some problems can occur during the healing of LASIK flap.Collagen crosslinking was that inductor could be activated, and then reactive oxygen species (ROS) or free radicals were generated. The ROS or free radicals could increase formation of covalent bond between collagens, in order to add the optical density of covalent bond between collagens, increase the fiber diameter and tolerance to proteolytic enzyme and the mechanical stiffness of the collagen fiber. Experiments proved that collagen crosslinking induced by Riboflavin/UVA could increase the fiber diameter, improve the ductility of cornea collagen, add tolerance to proteolytic enzyme, promote healing of corneal wound.The method had been used in clinical treatment, especially for keratoconus.The purpose of this study was to investigate the effect of collagen cross linking on the promoting the healing of the corneal flap after LASIK. For this purpose, cornea flap tensile resistance, coneal transparency and inflammatory reaction were observed.Methods1. Creation of LASIK models of rabbitLASIK flaps were created in both eyes of24health New Zealand rabbit corneas. The right eyes were experimental groups which were induced cornea collagen cross linking while left ones were control groups. After the operation, both of eyes were given with levofloxacin eye drops (four times a day) for three days.2.Examination of anterior segment with slit lampThe edema and inflammation reaction of corneas were observed with slit lamp at different time points (1d,3d,7d after surgery) in the experimental groups and control groups.3. Confocal microscopy examination At different time points (1w,1mths,3mths after surgery), corneas were observed with confocal microscopy in the experimental groups and control groups4. Histopathological examination of corneasTo obtain the cornea of experimental animal at different time points (1w,1mth,3mths after surgery). Histopathological examination with HE stain was performed..To observe the difference of inflammatory cell infiltration and keratocyte distribution in corneas between experimental groups and control groups.5. Electron microscope examinationCorneal electron microscope examination was performed at different time points (1mth,3mths after surgery). The diameter of cornea collagen fiber of both of groups were measured.6.Corneal flap tensile resistance experimentThe adhesion of corneal flap and corneal stroma was detected through tensile resistance experiment at different time points (lm,3m after surgery).Result1. The slit-lamp examination showed that yellow-green riboflavin could be found in anterior chamber after20min, which suggested that riboflavin could penetrate the corneal stroma without divesting corneal epithelial cells.2.There was no difference about cornea edema and hyperemia between experimental group and control group at different time point (1d,3d and1w after surgery) with slit lamp.3.At different time after LASIK(lw,lmth,3mths), confocal microscopy observation showed there were more apparent active keratocytes in experimental groups.4.Pathology examination showed that there was no obvious infiltration of inflammatory cells in experimental groups and control groups. And there was "No cell zone"in both groups.5.In electron microscope examination, the mean collagen fiber diameter of experimental groups (36.51±3.29nm) was bigger than control groups (29.55±1.74nm),(P<0.01), and the difference had statistical significance.6.The adhesion of the corneal flap and the cornea stroma in experimental groups was stronger than control groups after one monthConclusionAnimal experiment with photodynamics cornea cross linking can promote the adhesion of LASIK flaps. Cross linking may be as a promising method to prevent the displacement of corneal flaps after LASIK. |
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