| Retinal vein occlusion (RVO) is a common retinal ischemic disease in ophthalmology. But its pathogenesis has not been known thoroughly at all. If left untreated it can develop capillary nonperfusion and retinal neovascularization, which often cause vitreous hemorrhage, traction retinal detachment and neovascular glaucoma, and result in severe visual loss. Vascular endothelia growth factor (VEGF) is an angiogenic factor that also a potent mediator of increased vascular permeability. It is upregulated by hypoxia. The recent study demonstrated that level of VEGF was increased in the retina and vitreous body of patients and animals with ischemic retinopathies. To study further the effect of VEGF on RVO, this study adopted rabbit model of RVO, observed retinal vessels by funds f luorescein angiography, and compared VEGF expression between the RVO model group and the normal control group. The purpose was to find out the relationship of VEGF expression in the developmental process of retinal vein occlusion and the VEGF function on angiogenesis.Materials and Methods1. Animals and groups: The Matural and healthy pigment rabbits were chosenand randomly divided into normal control, retinal vein occlusion ltbweek, 2thweek and 4thweek groups. Each group consisted of 4 eyes.2. RVO model: RVO was established with intraocular electrocoagulation to retinal vein next to the disc. The length is 2/3PD and 6~8% power was used until the vein occluded completely. In normol control group, the vitreous body which 2mm far from the corresponding retinal vessels was electrocoagulated. The same length and same power were performed.3. Fundus examinataion: The retina and retinal vessels of the eyes were observed by ophthalmoscope, fundus color photography and fundus fluorescein angiography at each time spot.4. Histopathology examination: At the experimental ends of each group, the rabbits were air- embolized and their eyeballs were extracted. After fixation, the tissues were selected at 1pd or 4pd far from the optic disc and embedded in paraffin. 4um sections were prepared for hematoxylin and eosin and immunohistochemistry. An eye was chosen randomly in 2thweek group. The tissues were selected at 3pd far from the optic disc for transmission electron microscopy and the rest tissues were performed with the other eyes.5. Iramunohistochemical analysis: VEGF protein expression was detection by the Envision two-step immunohistochemical techniques.6. Morphologic quantity: The positive cell numbers on VEGF staining section were observed with light microscopy under 400 visula field. Two sites were selected randomly. Immunohistochemical quantity, which based on intensity and the percentage of positive vessels, was used to analyse the results with double mask. The mean was used as the parameter of this specimen.7. Statistical analysis: All data were managed with SPSS 11. 0 for window.The Least-significant difference , Dunnett ANOVA analysis and Paired-samples T test were used.Results1. Immediately after intraocular electro-coagulation, vein was occluded completely. Venous dilation, engorgement were the ophthalmoscopic changes. In the period of 2-3 day after occlusion, flame-shaped haemorrhages along with the veins and severe edema in the posterior pole could be seen. Venous collaterals were observed at 1 week after RVO which appeared collateral brush. The vascular channels always connected an occluded with a patent vein, and arose from the pre-exsiting capillary bed. Funds fluorescein angiography appeared microaneurysm and capillary nonperfusion. Under light microscopic examinations, HE stained sections showed cell structure disturbed, blood vessels congested, vascular endothelial cells detached from basement membrane and the nerve fiber layer appeared vacuole. By 2 weeks after RVO, recanalization of occluded vessels was observed or the early collateral formation was evident. Microvascular changes regressed gradually and regional capillary nonperfusion became small. Observation with electron micros...
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