| Background and ObjectiveSince the first ruby laser was utilized in patient treatment, there have been more than ten kinds of laser used in ophthalmology. Because its superiority process and certain effect, laser treatment has taken important position in ophthalmiatrics, especially in retina diseases. The laser photocoagulation has been used for treatment of retinal vascular diseases, such as diabetic retinopathy, retinal vein occlusions, and retinopathy of prematurity; for sealing of retina holes; for photocoagulation of the trabecular meshwork, iris, and ciliary body in the treatment of glaucoma; and for the treatment of intraocular turners. It is one of the most effective therapy for the retinal ischemia disease.Despite its widespread clinical use and excellent therapeutic efficacy, the exact mechanism of photocoagulation have not been determined. Presently, there are several presumptions: First, Part of the retina has been destroyed after photocoagulation, the area of the retina decreases, so result in the improvement of nutritional status of the remnant retina. Second, The retina atrophies and thinningzs after photocoagulation, so the diffusion of oxygen from the choriod into the inner retina becomes easier. Accordingly, the hypoxia of the retina is changed. Third, The neovascularization factor decreases because of the destruction of partial retina. Fourth, The damage of the extra-barrier after photocoagulation promotes the diffusion of neovascularization factor from the retina into the choroid.The normal tissue is also subjected when laser photocoagulation, so complications following the treatment is hard to avoid, such as hemorrahge, epiretina membrane, retina holes, choroidal neovascularization and macular edema. There is now increasing interest in how to minimizing unnecessary retina damage while obtaining therapeutical effect.The main site of energy absorption in laser photocoagulation is the melanin pigment in the retinal pigment epithelial (RPE) cells and the choroid. Physiologically, RPE cells produces kinds of cytokines and growth factors. Laser photocoagulation can cause RPE cells to change their shape and growth pattern, in addition, the profile of growth factor and cytokine production. Vascular endothelial growth factor (VEGF) and pigment epithelium derived factor (PEDF) working as the primary angiogenic growth factor and angiogenin inhibitor play much important part of the physiological and pathological angiopoiesis, and which is also the focus of recent years research.This study is to establish the retinal laser photocoagulation model in pigment rabbits. Subsequently, observe the histopathological change of the retina and the reparative process of RPE, and detect expression of PEDF and VEGF in the retina before or after photocoagulation. Accordingly, to approach the therapeutic mechanisms of retina laser photocoagulation.Materials and Methods15 normal pigmental rabbits were used and devided into two groups randomly: experiment group and control group, which included 12 rabbits (24 eyes) and 3 rabbits (6 eyes) seperately. The experiment group was devided into four subsets depended on different times: 1d, 3d, 7d, 28d. And each group contained 3 rabbits (6 eyes). Laser photocoagulation was performed (75mW, 200μm, 0.1s) on the both eyes of the experiment rabbits, and the irradiated site located at posterior pole retina, 2PD distanced from the optic disc. The rabbits were killed at intervals, one eye was prepared for RPE whole mounts, and the fellow eye was used for pathological section. The damage and repairation of the RPE was determined in RPE whole mounts; Histopathological effects of the retina and choroid were observed through light microscope; The expression changes of PEDF and VEGF were detected by histochemical stain.The data were analyzed with statistical software SPSS12.0. Numerical data were expressed with x|-±s. Several groups were compared by simple factor analysis of variance, and every two groups were compared by q test. Results were considered significant at a=0.05.Results1. Fundus image: The fundus of nomal pigmental rabbit looked clearing and thin. The pigmentary layer and choroidal vessels could be seen clearly. Retinal edema appeared after photocoagulation, with white color laser spot. Then the retinal edema decreased gradually. The color of laser spot became gray, and there was confluent tendency among the laser spots.2. RPE whole mounts: RPE was a monolayer tissue. The size and shape of the cells were fairly uniform, which looked like sexangle slabstone lined up in order. After photocoagulation, cells around the laser spot became heterogeneous in size, shape and pigmentation. Cellular necrosis, atrophia and absence could be detected in the laser spot. Then the damage was recovered by the proliferation and aversion of RPE cells around the laser spot.3. Histopathological examinations: laser photocoagulation caused disorganization of outer retina, cell necrosis, nuclear fragmentation and disintegration, inflammatory cell could be found, Subsequently the proliferous RPE and fibroblast repaired the destroyed areas of retina.4. Immunohistochemistry: The expression of PEDF and VEGF of the control group could be detected in photoceptor layer, internal granular layer and ganglion cell layer. PEDF protein levels significantly increased after laser photocoagulation. PEDF concentrations were maximum at day 3, and stayed elevated until day 28. Expression of VEGF was increased 1 day after photocoagulation, which declined to the control levels at day 3 and below the control levels statisticly at day 28. Conclusions1. Disorganization and cell loss in the outer retina could be detected after laser photocoagulation. Subsequently, the proliferous RPE and fibroblast repaired the destroyed areas of retina.2. Laser phtocoagulation induced the proliferation of RPE, which play an important parts in the RPE reparative process.3. Laser photocoagulation induced upregulation of PEDF and downregulation of VEGF, which caused new balance between angiogenesis factor and inhibition factor, so inhibit the neovascularization. |
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