Dilated pupils on one side and narrowed pupils on the other side may be due to diseases of the eye or the central nervous system. 1. Eye diseases: If the eye is traumatized, damage to the motor nerve can cause the pupil to appear large or small. In addition, eye diseases such as glaucoma and iritis can also cause pupil size discrepancy when one eye is affected. 2. Central nervous system diseases: brain hernia, cerebral hemorrhage, brain tumor, cerebral infarction and other central nervous system diseases usually increase the pressure on the brain, which leads to the pupil on one side to become larger or smaller. The symptoms of dilated pupils on one side and narrowed pupils on the other side alone cannot accurately determine the disease, and it is necessary to combine the examination results and medical history to make an accurate judgment. It is recommended that when the patient finds that the pupils of both sides are not equal in size, he should go to the hospital in time to do further examination under the guidance of the doctor to clarify the cause of the disease in order to obtain the best treatment plan.