The cornea, iris, and lens in front of the eyeball are defined as the anterior segment by the ophthalmology community, and the vitreous body, retina, and choroid in the back are defined as the posterior segment. The bottom of the posterior segment is called the fundus. The fundus is composed of the retina, fundus blood vessels, optic nerve head, optic nerve fibers, the macula on the retina, and the choroid behind the retina. The lesions in these parts are collectively referred to as fundus diseases. The harm of fundus diseases to people is mainly to affect visual ability, and severe cases can cause blindness. Fundus diseases are a disease with many types, complex causes, and variable conditions. The early symptoms of fundus diseases around the fundus are often not discovered by patients. When patients feel that their vision is declining, the course of the disease may have been very serious. For the central part of the fundus, such as the macula, optic nerve, etc., once lesions occur, vision can be affected. Fundus diseases, like other human diseases, can be acute or chronic. The development process of some diseases can last for several years or even more than ten years, and for some acute diseases, if they are not rescued in time, they can cause blindness. For example: central retinal artery occlusion. There are also some fundus diseases that can heal without treatment, but they may recur, such as central serous chorioretinopathy. Many fundus diseases are related to systemic diseases, such as diabetes, kidney disease, hypertension, bacterial diseases, parasites, and brain diseases.