From the Guidelines
Pinpoint pupils, or miosis, are caused by several conditions that affect the iris muscles or the nervous system controlling pupil size, including opioid use, certain medications like pilocarpine, neurological conditions such as Horner's syndrome, toxic exposures, and inflammatory conditions of the eye. The most common causes of miosis include:
- Opioid use (such as morphine, heroin, fentanyl, or oxycodone), which activates parasympathetic receptors in the eye 1
- Certain medications like pilocarpine eye drops used for glaucoma treatment, which directly stimulate pupil constriction 1
- Neurological conditions such as Horner's syndrome (caused by damage to the sympathetic nerve pathway) or pontine strokes affecting the brainstem, which can result in pinpoint pupils 1
- Toxic exposures to organophosphates (found in some pesticides), which inhibit acetylcholinesterase, leading to excessive parasympathetic stimulation and pupil constriction
- Inflammatory conditions of the eye like iritis or uveitis, which may also cause miosis as part of the inflammatory response In critical situations, pinpoint pupils can indicate life-threatening conditions such as opioid overdose (accompanied by respiratory depression) or brainstem hemorrhage (with other neurological symptoms) 1. The mechanism behind miosis involves either excessive stimulation of the pupillary sphincter muscle through parasympathetic pathways or inhibition of the sympathetic nervous system that normally promotes pupil dilation 1.
From the FDA Drug Label
Pilocarpine is a cholinergic parasympathomimetic agent exerting a broad spectrum of pharmacologic effects with predominant muscarinic action. Pilocarpine, in appropriate dosage, can increase secretion by the exocrine glands The sweat, salivary, lacrimal, gastric, pancreatic, and intestinal glands and the mucous cells of the respiratory tract may be stimulated. When applied topically to the eye as a single-dose it causes miosis, spasm of accommodation, and may cause a transitory rise in intraocular pressure followed by a more persistent fall Pilocarpine hydrochloride tablets are contraindicated in patients with... when miosis is undesirable, e.g., in acute iritis and in narrow-angle (angle closure) glaucoma.
The causes of miosis (pupillary constriction) include:
- Cholinergic parasympathomimetic agents such as pilocarpine
- Acute iritis
- Narrow-angle (angle closure) glaucoma 2, 2
From the Research
Causes of Miosis
- Opioid toxicity: Opioids can cause a well-recognized toxidrome including respiratory depression, decreased conscious level, pinpoint pupils, and drop in blood pressure 3.
- Olanzapine intoxication: Overdosing olanzapine can cause tremor, bradykinesia, hypotension, somnolence, coma, and miosis 4.
- Valproic acid poisoning: Clinical features of valproic acid poisoning can include profound coma, depressed respiration, and miosis 5.
- Horner's syndrome: A neurological disorder characterized by a disruption in the sympathetic nerves to the face and eye, which can cause miosis, among other symptoms 6, 7.
- Autonomic innervation disorders: Disordered autonomic innervation of the iris can lead to abnormal pupillary responses, including miosis 6.