Pupils less than 0.0079 inches (2 mm) in normal light settings are called abnormal miosis or pinpoint pupils. Several medical conditions can cause this to occur, including stroke, drug use, and head injury. In addition to serious medical issues, pinpoint pupils can be caused by looking into a bright light or taking certain medications. The cause of constricted pupils should be considered alongside other physical symptoms to assess whether immediate medical treatment is needed.
Pupils typically react to light. In normal settings, the pupil is round and medium sized when compared to the rest of the iris. Normal pupils react to light by constricting. The amount of constriction relates to the contrast between dark and light that the pupil is exposed to. In a pitch-black room, when a light is shone directly into a pupil, it can constrict to the size of a pinpoint; however, as the pupil adjusts to the light, it should dilate, though not to a normal size as long as the light is on it.
Depending on the region and setting, the most common cause of pinpoint pupils is use of opiate narcotics. Examples of opiates include heroin, codeine, methadone, morphine and oxycodone. Pinpoint pupils combined with slowed breathing is a classic symptom of an opiate overdose. Overdoses occur among medical patients taking prescribed medications as well as drug users taking illegal substances. Heavy opiate use among drug abusers can also cause pinpoint pupils without the user actually overdosing.
Brain hemorrhaging is another cause of pinpoint pupils. Hemorrhaging can happen with traumatic brain injury, stroke, or illness. If the hemorrhage is at the front of the brain stem, both pupils will typically be constricted. If the injury is in other areas of the brain, pupils may be different sizes, with one dilated and the other pupil constricted. The pupil constriction in a person with a history of stroke or other brain trauma should be evaluated for hemorrhage.
Exposure to certain chemicals, including organophosphates, can constrict pupils to pinpoints. The chemicals cause overstimulation of the parasympathetic system, which in turn makes the pupils constrict significantly. Pesticides often contain chemicals that cause pupils to constrict with overexposure. A patient with constricted pupils who recently used pesticides should be examined for pesticide poisoning. Patients will typically have increased body fluids as well as overall muscle cramps, in addition to pinpoint pupils.
Occasionally, constricted pupils are due to a rare physical disorder, such as Horner syndrome. Horner syndrome is usually the result of an underlying medical issue such as a stroke, but sometimes it occurs alone. Pinpoint pupils are a classic symptom of the disorder, along with drooping eyelids and a reduced ability to perspire on the affected side of the face. The disorder typically only impacts the face and eyes. Babies born with the syndrome will have one iris lighter than the other, as well as constricted pupils.
