The size of the pupil always changes depending on the distance, light Intensity, as well as the drug effect change. In fact, in people's life, pupil size with the age growth make a periodic change, 1 year old child has smaller pupil diameter due to the eye muscle develop incompletely. Young people and adults have lager pupils. 40 years old and older people have complex narrow pupil diameter. And the pupil of myopia greater than hyperopia, clear greater than sleep. Strong light stimulus, emotional excited and violent pain will change pupils narrow. In short, in normal circumstances, the size of the pupil is in continuous dynamic changes.