Central retinal vein occlusion is one of the most common clinical fundus diseases that can easily lead to vision loss. I. Etiology and pathogenesis The factors that produce retinal vein obstruction are complex, often a combination of factors, but for a particular patient, one of them may be the main pathogenic factor. In general, hypertension, hyperlipidemia, atherosclerosis. Inflammation, blood hyperviscosity and hemodynamics are all related to the development of retinal vein obstruction. 1, anatomical factors In anatomy, the epiretinal membrane at the intersection of the central retinal vein and artery is common. the site of RVO is closely related to the characteristics of its arteriovenous intersection point and the distance from the disc edge. In BRVO, the relationship of retinal arteriovenous crossings and the distance of the first crossed branch from the disc rim are the main risk factors for the development of BRVO. The branching of the retinal vein, the entry into the optic papilla, and the exit from the optic nerve are all at nearly right angles to the sieve plate and the optic dura, both of which predispose to obstruction formation. In addition, the short eye axis and the occurrence of RVO also have a certain relationship. 2, vascular sclerosis and endothelial hyperplasia In the scleral sieve plate, the central retinal artery and vein are adjacent to each other, with close anatomical relationship and surrounded by a common connective tissue sheath. When the surrounding connective tissue or and the central retinal artery sclerosis thickening, the vein is easily compressed; sclerosis evolution can also directly invade the vein, so that the vein wall itself sclerosis thickening, resulting in gradual irregular narrowing of the lumen of the vein, in the inner surface of the wall in one or more places in contact with each other, causing endothelial hyperplasia or secondary thrombosis and complete obstruction. The obstruction due to such causes is mostly in middle-aged patients, often with hypertension (70.9% a 99%), retinal atherosclerosis and diabetes mellitus and other systemic diseases. 3, vascular inflammation, thrombosis Any systemic and ocular local inflammation can invade the retinal vein, and retinal vein obstruction occurs. In case of influenza, septicemia, pneumonia, tuberculosis, dengue and orbital cellulitis, if pathogenic microorganisms infect the retinal veins or toxins from inflammation make the inner surface of the canal rough, then thrombosis can occur and the canal lumen can be closed. Cases of combined central or branch retinal vein obstruction in patients with peripapillary retinal veinitis are not uncommon in clinical practice. Retinal vein obstruction due to inflammation is mostly seen in young patients under 40 years of age. 4. Blood rheology abnormalities The vast majority (82%) of patients with retinal vein obstruction have hyperlipidemia. Plasma viscosity and whole blood viscosity are often higher in most patients than in controls. Some have increased erythrocyte pressure, fibrinogen and immunoglobulin compared to controls. In addition, erythrocytosis and macrohemoglobinemia increase blood viscosity, and the decrease of prothrombin factor III promotes blood clotting, which also facilitates thrombosis. The occurrence of retinal vein occlusion (RVO) is closely related to the systemic vascular changes caused by various causes; in recent years, it has been found that various hemodynamic factors play an important role in the occurrence of RVO. Patients with venous obstruction are often triggered by inadequate arterial blood supply. The decrease in blood flow rate and flow in the central retinal artery causes a decrease in retinal artery perfusion pressure, resulting in RVO. 6, other oral contraceptives, increased intraocular pressure and head trauma. Excessive fatigue, emotional excitement is also an obvious cause of this disease. The main symptom of central retinal vein obstruction is visual impairment, which often occurs suddenly, and the visual acuity can be reduced to several fingers or can only distinguish manual, and there are also those who have gradual vision loss within a few days; there can be a history of transient vision loss. The peripheral visual field is often normal or has irregular centripetal narrowing. The central visual field often has a central or paracentral dark spot. 2. Fundus: The optic papillae are congested and mildly swollen, red in color with blurred borders. The retinal veins are stagnant and purple in color. They are irregular in diameter, significantly dilated, and may be waxy or even nodular in shape. Retinal arteries may be narrowed due to reflex functional constriction or pre-existing atherosclerosis. The retina is edematous or even markedly elevated, and the retinal vessels are obscured in the hemorrhagic edematous tissue. The entire fundus is covered with retinal hemorrhagic spots of varying size. The hemorrhage is mainly in the superficial layer and is flame-like. The macula often has diffuse or cystoid edema and hemorrhage.