From the Guidelines
Pinpoint pupils, also known as miosis, are primarily caused by opioid use, certain medications, and neurological conditions that affect the parasympathetic or sympathetic nervous systems controlling pupil size. Common causes include opioid use (such as morphine, heroin, fentanyl, or oxycodone), which activates parasympathetic receptors causing pupillary constriction, as noted in the 2024 American Heart Association and American Red Cross guidelines for first aid 1. Certain medications like pilocarpine eye drops, cholinergic drugs, and some antipsychotics can also produce this effect. Neurological conditions that may cause pinpoint pupils include Horner's syndrome (due to damage to the sympathetic pathway), pontine hemorrhage or infarction (often called "pontine pupils"), and neurosyphilis. Additionally, toxic exposures to organophosphates (found in pesticides) and some mushroom poisonings can cause miosis by inhibiting acetylcholinesterase, leading to increased acetylcholine levels.
Some key points to consider:
- Opioid overdose is a critical condition that may present with pinpoint pupils, requiring immediate medical attention with naloxone administration, as emphasized in the 2024 guidelines 1.
- Neurological conditions such as cerebellar infarcts with swelling can lead to brainstem compression, resulting in pinpoint pupils, as described in the 2014 recommendations for the management of cerebral and cerebellar infarction with swelling 2.
- In the context of primary angle-closure disease, pinpoint pupils may be a sign of increased intraocular pressure, and treatment with parasympathomimetics or other agents may be necessary to reduce IOP, as discussed in the 2021 Primary Angle-Closure Disease Preferred Practice Pattern 3.
In critical situations, pinpoint pupils may indicate life-threatening conditions such as opioid overdose or brain stem injury, requiring immediate medical attention. The underlying mechanism typically involves either excessive parasympathetic stimulation or inhibition of sympathetic input to the pupil, disrupting the normal balance that maintains appropriate pupil size in response to light and other stimuli.
From the FDA Drug Label
Morphine causes miosis, even in total darkness. Pinpoint pupils are a sign of opioid overdose but are not pathognomonic (e. g., pontine lesions of hemorrhagic or ischemic origins may produce similar findings). Marked mydriasis rather than miosis may be seen due to hypoxia in overdose situations. Acute overdose with morphine sulfate tablets can be manifested by ... constricted pupils ...
The causes of pinpoint pupils (miosis) include:
- Opioid overdose
- Pontine lesions of hemorrhagic or ischemic origins 4 Note that marked mydriasis may be seen in cases of hypoxia in overdose situations, rather than miosis [4] [5]
From the Research
Causes of Pinpoint Pupils (Miosis)
- Opioid use is a common cause of pinpoint pupils, as seen in studies 6, 7, 8, 9, 10
- The accumulation of active metabolites of opioids can cause a well-recognized toxidrome, including respiratory depression, decreased conscious level, pinpoint pupils, and drop in blood pressure 6
- The pupillary effects of opioids are dose-related, with higher doses causing greater decreases in pupillary size and velocity of constriction to a light stimulus 8
- Different opioids, such as morphine, codeine, and tramadol, can cause varying degrees of miosis, with morphine and codeine causing a 26% decrease in pupil diameter 9
- Opioid-induced hypercarbia and hypoxia can also affect pupillary responses, but the light reflex remains quantifiable during opioid-induced toxicity 10