The pupil is innervated by the pupil opening muscle and the pupillary sphincter, and its size is also determined by the movement of these two groups of muscles in different situations. The factors that influence this are as follows: 1) age, the older the person, the smaller the pupil may be; 2) racial factors, oriental people will have slightly smaller pupils than westerners; 3) refractive state, myopic patients may have slightly larger pupils, farsighted patients may have slightly smaller pupils; 4) light intensity, when the light is strong the pupil will become smaller, when the light is weak the pupil will become larger 5, the body’s ability to adjust, the body itself has the ability to adjust, for example, when looking at something far away, the pupil may unconsciously larger, while looking at something near the pupil will unconsciously smaller; 6, emotional factors, such as very anxious, angry, the pupil will suddenly become a little larger. However, these are not pathological phenomena. Of course, some drugs can also cause pupils to become smaller in clinical practice. For example, medications such as brassinosteroids may cause pupils to become smaller, but this varies from person to person.