The pupil is the black area of the eye in the centre of the iris that expands and contracts to let light into the eye. When light becomes brighter, the pupil contracts. When light dims, the pupil dilates to let more light into the eye. Pinpoint pupils are when the pupil has contracted to less than 2mm across. Pinpoint pupils can be caused by opiate drug use, exposure to certain nerve-damaging chemicals or brain damage. To get a diagnosis of pinpoint pupils, you must alter the light source around the person.
Cover the person's eyes completely with your hand. You can also turn the lights off in the room. Wait 3 to 5 seconds to give the pupils a chance to dilate in response to the darkness.
Move your hand away from the person's eyes and quickly shine a small flashlight into the person's eyes. The pupils should rapidly contract in response to the newly introduced light source.
Watch the activity of the pupil closely. If the pupils remain at less than 2mm in diameter despite the light changes, the person has pinpoint pupils, which is a sign of drug use or brain damage.