A small eye at the back of the anus may be formed due to heredity or may be caused by an anal fistula. During the growth and development of fetuses and newborns, a pit similar to a small eye may form 1-2㎝ behind the anus due to abnormal development of the end of the tailbone, but it has no effect on the normal function of the anus. As long as there is no organic damage to the skin or mucus leakage, no treatment is needed, and the pit will gradually recover after the development becomes normal. If the fistula is typical, feces and mucus will flow out of the small eye and the patient will have symptoms such as swelling and pain, and itching will occur due to long-term stimulation of mucus and feces. It is recommended to distinguish the symptoms and performance carefully and seek medical attention in time.