Pupil dilatation means that the diameter of the patient’s pupil becomes larger, and the patient can usually experience discomfort such as photophobia and blurred vision. The pupil is located in the center of the iris in the eye, and is the channel through which light enters the eye. The diameter of a normal pupil is generally around 2~4 mm, and is sensitive to normal light reflexes. When the pupil is dilated, the diameter of the patient’s pupil becomes larger, because more light enters the eye, the patient may appear photophobic performance, but also the discomfort of blurred vision. Dilated pupils can be caused by head injuries, eye diseases, and other illnesses. It is recommended that patients with abnormal pupils consult a hospital in a timely manner to assess their condition and follow the doctor’s instructions for treatment.