chronic inflammatory disease of the eye (eye disease) caused by Chlamydia trachomatis, a bacterium-like microorganism that grows only within tissue cells of the infected host. The conjunctiva becomes thickened and roughened, and deformation may result. Extension of inflammation to the cornea occurs in varying degree; resultant scarring can lead to corneal opacity and blindness. Transmission occurs by personal contact with infective ocular secretions or indirectly by common use of a towel.

Trachoma occurs especially under conditions of poverty, overpopulation, or poor sanitation and is often complicated by other eye infections of bacterial origin. One of the oldest diseases known to man, trachoma is present in most areas of the world and is especially prevalent in Asia and North Africa. In the United States after about mid-20th century, most cases were limited to a few localities, particularly among native Indian populations. A conjunctival infection of newborns (inclusion conjunctivitis) is caused by a similar disease agent found in the birth canal of the mother. Beginning in 1957 with the discovery that the trachoma microorganism could be grown in the laboratory, fundamental studies on the disease agent, as well as development of experimental vaccines, became possible.

The sulfonamide drugs, as well as some of the antibiotics, are curative.