The appearance of trachoma is one of the symptoms of trachoma. Trachoma is a chronic infectious conjunctival keratitis caused by Chlamydia and is one of the most blinding eye diseases. Trachoma is named after the rough and uneven appearance of the conjunctival surface, which resembles sand grains. In the early stages of the disease process, there is infiltration of the conjunctiva, such as papillae and follicular hyperplasia, and corneal vascular opacification; in the late stages, scarring of the affected lid conjunctiva leads to inversion of the eyelid, which aggravates the damage to the cornea and can seriously affect vision and even cause blindness. What causes the trachoma appearance of the lid conjunctiva? In 1907, Halbestaedter and Prowazek used light microscopy and Giemsa staining to find inclusion bodies in the epithelial cells of the trachoma conjunctiva, i.e., epithelial cells with aggregations of red-blue proto- and dark-blue initiating particles, which have a matrix, rather like an outer coat, and were mistakenly called chlamydospores ( chlamydozoa). Since then, a number of studies have been conducted successively. However, the pathogen of trachoma was not isolated for the first time until 1955 by Fei-Fan Tang and Xiaolou Zhang in China using the chicken embryo culture method. Since this pathogen can pass through bacterial filters, parasitize in cells and form inclusion bodies, it was considered a virus at that time. It was also called an atypical or large virus because its size and morphology were different from those of general viruses, similar to the large viruses of parrot fever and lymphogranuloma. Since then, scholars from various countries have further studied its molecular biology and metabolic functions, and proved that it has RNA, DNA and certain enzymes, reproduces by bifurcation, has a cell membrane and wall, and is sensitive to bacteria, etc. These are not consistent with the nature of a virus, but have many similarities with Gram-negative bacteria. Therefore, the Bergey Manual of Bacterial Identification, published in 1974, created a separate category of this group of microorganisms called Chlamydia. Chlamydia trachomatis is one of them. Chlamydia trachomatis can be classified antigenically into 12 types, including A, B, C, Ba, D, E, F, G, H, I, J, and K. Trachoma in endemic areas is caused by types A, B, C and Ba, while the other types cause genitourinary infections and inclusion body conjunctivitis. Some authors refer to the former types as the epidemic Chlamydia trachomatis group and the latter types as the ocular and genitourinary Chlamydia groups. Chlamydia trachomatis has 2 biological phases in its life cycle, i.e., the primary body and the initial body. The elementarybody is the infectious phase, about 0.3micro;m in size, has a cell wall, and can survive outside the cell. The initialbody, also called reticulatebody, is the reproductive phase and is larger, about 0.8 micro;m, and is not infectious. After the protozoa invade the host cell, they develop and transform into the initiating body in the cytoplasm, and form the daughter protozoa by bifurcation. When the cytoplasm is full, it ruptures and releases the protozoa, and the free protozoa then invade the normal epithelial cells and start a new cycle. Each cycle lasts about 48 h. The incubation period is 5 to 14 days, and the disease is bilateral, occurring mostly in children or at a young age. In mild cases, trachoma can be completely free of conscious symptoms or only have mild itching, foreign body sensation and small amount of discharge. In severe cases, due to sequelae and complications involving the cornea, there are irritating symptoms such as photophobia, lacrimation, pain and self-conscious loss of vision.