The normal diameter size of the pupil is 2.5-4mm. If the pupil is <2mm in diameter, it is called a miosis. There are many causes of pupil narrowing, such as bright light exposure, and the pupil will narrow significantly, which is a physiological manifestation. In addition, some drugs can also cause pupil narrowing, such as organophosphorus poisoning, which can cause pinpoint pupils, and this usually requires prompt resuscitation treatment at a regular hospital. In addition, some eye diseases may also cause pupil narrowing, such as acute iritis. In conclusion, it is important to take a careful medical history and examine the patient to determine the cause of the narrowed pupil and, if necessary, to seek active treatment at a regular hospital to prevent adverse reactions.