| PerfaceWidely used in clinical practice with better predictability and stability, Photorefractive keratectomy (PRK) is one of the best methods to treat myopia. But a lot of researches confirmed that fluorine can cause the toxic reaction of the cornea. Studies in vitro also show that 193nm excimer laser, when working, may produce 295 ~ 320nm secondary laser which would reach such tissues as lens and retina. Beginning from animal experiments, we will study the effects of excimer laser on free radical reaction of ocular tissues.This research will provide us with theoretical foundation, whether PRK (especially for high myopia) or re - ablating for refractive recession , those can result in cornea and lens injury and bring about a seri-al of complications. Meanwhile, the study will offer us reference and guide clinical practice safer, more reasonable and more effective.Subjects and Methods1. Material and groups45 (90 eyes) white rabbits were randomly divided into three groups. The corneal epithelium was removed with a blunt spatula in group I , II and III. We performed 48 um corneal photoablation in group II (30 eyes) , and 86um corneal photoablation in group III (30eyes) after deepithelialisation. The three group of rabbits were sacrificed respectively after operation in the different time (12h,24h, 72h. 7d and 14d). Another 3(6 eyes) rabbits was the control group.2. Surgical TechniquesAll rabbits were treated by a Summit Apex Plus Laser system with the procedure of Single Zone Lasik with Pretreatment. After general anesthesia was done with 1 ml/kg of 10% solution injected into muscle , we measured the central depth of cornea, then we conducted PRK in double eyes of rabbit according to predicative corrected degrees. Guttae Chloromycetin was used after operation.3. Observing items and methods6 eyes of each group were taken at respectively after operation. Then we cut the central comeal tissues, extract the lens, and put them into dry and hard plastic tubes. Afterwards we detected the activities of superoxide dismutase ( SOD) and glutathione peroxidase ( GSH -PX).4. Statistical analysisT - test was done respectively between two groups and square a-nalysis was within one group.Result1. Dynamic changes of the activities of the corneal SOD,GSH -PX at different time'after operation.By t -test, SOD activities of each group at 12th , 24th hour andGSH - PX activities at 24th hour have significant differences comparedwith the control group ( p < 0. 01). SOD activities of group HI andI , II at 7th day and 14th day, GSH - PX activities at 7th day postoperation ( p <0.01) showed significant differences. Using square variance test, the SOD activities in the same group have significant differences between 14th day and other times( p <0. 01) .2. Dynamic changes of the activities of the lens SOD,GSH - PX at different time after operation.By t - test and square variance test, the SOD and GSH - PX activities in different group and at different time have no significant difference ( p > 0.05 ).DiscussionThe dominant pathological changes after PRK are as follows: there are the neutrophil infiltration beneath ablating surface at 24th hour after operation, which still exist at 4th day despite of obvious decreases, with a few macrophages there. We didnt see the neutrophil infiltration at 7th day, but we see a few distributed stromal cells. By phagocytosis and when activated by soluble materials, neutrophil can produce respiration burst, which result in the quantities of free radi-cal.Although organisms are damaged by free radical to some extent, they also develop some certain defensive functions against free radical, by the way of producing successively the subject to defence free radical, including the antioxidant enzyme and the antioxidants. The an-tioxidant enzyme are mainly composed of SOD , GSH - PX and CAT, which can eliminate the free radical effectively.In our experiment, the SOD凣SH - PX activities in cornea and lens are all different at d... |
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