A small eye above the anus may be the external opening of an anal fistula, which consists of an internal opening, a fistula tube and an external opening. The anal fistula comes from an infection of the internal sinus, which breaks down to form an internal opening, and the internal opening produces inflammatory exudate that continuously erodes the perianal tissue and gradually breaks down outside the anus. The fistula is a small eye in the perianal skin, and the middle tube is the fistula, which is constantly overflowing with pus, sometimes closed, sometimes broken, and recurrent. The main symptoms of anal fistula are pus flowing around the anus, pain when the external opening is closed, itching and eczema when the pus stimulates the perianal skin, etc. The only treatment for anal fistula is surgery.