Trachoma is cause by an infection with the bacteria chlamydia trachomatis. It is the worlds leading cause of preventable blindness. Trachoma causes blindness through trachomatous conjunctival scarring - severe scarring on the inside of the eyelid that cause it turn onwards, leading to the eyelashes rubbing against the eyeball and scarring of the cornea. The blindness caused by trachoma is irreversible.