Diabetes mellitus is a common disease that seriously affects people’s health and life, and is second only to cardiovascular disease, cerebrovascular disease and cancer in terms of disability and death rate, accounting for the first three; clinically there are two common types, insulin-dependent or type L diabetes and non-insulin-dependent or type II diabetes. Type II diabetes is much more common than type I, accounting for more than 90% of all diabetics, and is most common in adults over the age of 40. About 70% of diabetic patients develop systemic small vessel and microangiopathy. Diabetic retinopathy is the most important manifestation of diabetic microangiopathy, and is one of the serious complications of diabetes. The most common complaints of diabetic patients are flashing sensation and loss of vision. In both non-proliferative and proliferative diabetic retinopathy, light scattering due to retinal edema often causes the patient to feel a flash of light. In non-proliferative lesions, macular edema, ischemia, or hard exudate invading the central sulcus is a common cause of vision loss, while large capillaries outside the macula are not perfused and do not cause conscious symptoms. In the proliferative phase, vitreous hemorrhage, proliferative vitreoretinopathy and retinal detachment can cause severe vision loss. The fundus manifestations of diabetic retinopathy include microangiomas, hemorrhagic spots, hard exudates, cotton wool spots, retinal vasculopathy, macular lesions, vitreous and optic neuropathy, etc. The important clinicopathological processes are the formation of microangiomas, retinal capillary and small artery atresia, neovascularization and fibrous tissue proliferation, intravitreal fibrovascular tissue contraction and complicating retinal detachment. The disease can be divided into non-proliferative diabetic retinopathy and proliferative diabetic retinopathy. The fundus manifestations of non-proliferative diabetic retinopathy include microangiomas, hemorrhagic spots, hard exudates, cotton wool spots, and vascular lesions. (1) Microangioma Retinal microangioma refers to a spherical or ovoid lateral bulge located in the small pre-capillary arteries, capillaries and small post-capillary veins of the retina, or, occasionally, in the retinal veins. Therefore, they are called microangiomas rather than microaneurysms. Microangiomas are the earliest diabetic retinopathy visible on fundoscopy and appear as well-defined red or dark red spots, usually less than 125 um in diameter, with clear, smooth borders, distinguishable from hemorrhages. Retinal microangiomas usually exist for a long time, but they can also become pink or have white edges due to thickening of the canal wall, vitreous degeneration, and natural obstruction of the capsule lumen, and finally form small round white spots. Microangiomas are often more numerous on fundus fluorescence angiography (fluoroscopy) than on fundoscopy. Small microangiomas are difficult to detect on fundoscopy, but can be seen on fluoroscopy. Microangiomas are often located on the capillaries surrounding the capillary atresia, suggesting that their occurrence is related to local tissue hypoxia, cystic dilatation of the capillary wall, and/or capillary endothelial proliferation. The formation of microangiomas is an important step in diabetic retinopathy. Leakage of microangiomas is an important cause of retinal edema, and their number and changes can reflect the severity, progression, or regression of retinopathy. Retinal microangiomas are not unique to diabetes mellitus, but can occur in many ocular diseases such as retinal vein obstruction, retinal perivasculitis, chronic uveitis, and some systemic diseases such as hypertension, nephropathy, anemia, and even in normal people. In addition, microangiomas can also be found in the conjunctiva and heart muscle of diabetic patients. (2) Hemorrhagic spots In the early course of the disease, the hemorrhages are usually small dots or circles, mostly located in the deep retina. The hemorrhage can be gradually absorbed, but new hemorrhage can appear nearby, as if the fundus had not changed. As the disease progresses, there may be superficial strip or flame hemorrhages, or even large subretinal or preretinal hemorrhages. (3) Hard exudate Hard exudate: a yellowish-white waxy spot with clear borders. They may appear in several or in piles. Sometimes they are arranged in a circular pattern around one or several microangiomas, and may also fuse with each other to form large patches. After the disease improves, it takes a long time to be gradually absorbed. (4) Cotton wool spots (soft exudate) Cotton wool spots: grayish white spots with unclear borders, mostly appearing near arteries or at the bifurcation of arteries in the early stage, generally about 1/4 to 1/3 of the diameter of the optic disc (DD), and occasionally as large as 1/2 DD. Hemorrhagic spots, microangiomas, and occasionally condensed and dilated capillaries can be seen on the margins, and some are surrounded by hard exudative rings. The cotton wool spots are usually slow to fade and can persist for months, with the old ones being pale and thin and flat with clear borders. After fading, it shows mild pigment disorder, and some of them have a bunch of hard exudate spots. In the same fundus, cotton wool spots of different ages can appear at the same time. When cotton wool spots appear in the fundus, it indicates that the diabetic retinopathy has been more serious, and if a large number of them appear, it means that the lesion is very active and may have entered the pre-proliferative stage. (5) Retinal vasculopathy 2. Diabetic retinal vasculopathy includes retinal arteries, veins and capillaries. (1) Retinal arteries In diabetic patients, there are two common changes in retinal arteries: ① Small artery occlusion: In most advanced and early stage patients, the small branches of retinal arteries are thin and narrow, and some of the small branches are almost thin lines, and the color is light and not easily recognizable. In severe cases, the larger branches may also appear as white lines or have white sheaths. In the areas with white-lined arteries, the retina is severely ischemic and hypoxic, with marked edema. In rapidly progressive fundus, this arterial white-linear change may develop from small branches to larger branches within 1 to 2 weeks, and in a few weeks, neovascularization from the veins may be seen extending into the area, with the white-linear artery often obscured by the neovascularization. On fluoroscopy, the diameter of the artery is irregular, the proximal end of the small branch is partially narrowed or even completely occluded, the distal end is slightly dilated, the wall is stained and leaking, and there are large areas without perfusion. Small arteriosclerosis: In diabetic patients of middle age or above with long duration of disease, retinal arteries show changes similar to hypertensive retinal arteriosclerosis; there are arteriovenous crossover signs, and the light reflection of the arterial wall is widened, even like copper wire. Some of these patients do not have a history of hypertension, and their blood pressure has been measured several times and is normal. Retinal arteriosclerosis is more severe in patients with hypertension combined with diabetes than in patients without diabetes in the same age group. (2) Retinal veins In the early stage of diabetic retinopathy, it is common to see the veins filled and dilated with dark red color, which is obvious in the temporal veins. In advanced cases, when the arteries have been altered, the veins may undergo a series of special changes: uneven diameter, shuttle-shaped, bead-shaped or globular dilatation, twisting and tripping, and limited diameter narrowing with white sheath or even partial or total occlusion. (3) Retinal capillaries In the early stage of diabetes mellitus, the fundus may be normal, but the capillaries may have pathological changes of basement membrane thickening. Later, the pericytes of the capillary wall gradually disappear, the endothelial cells proliferate, the lumen is gradually occluded, and cotton wool spots appear in the fundus, and the capillaries near them compensate for the dilation. Fluorescence imaging can clearly show capillary occlusion and dilation as well as microvascular abnormalities in the retina. More microangiomas can be seen in the periphery of capillary occlusion.