Benzodiazepines Do NOT Cause Mid-Dilated Pupils
Benzodiazepines do not cause pupillary dilation; they are associated with normal or potentially constricted pupils, not mid-dilated pupils. This is a critical clinical distinction when evaluating patients with altered mental status or suspected drug intoxication.
Pupillary Effects of Benzodiazepines
Benzodiazepines have no direct effect on pupil size and do not cause mydriasis (pupil dilation) through their mechanism of action as GABA-A receptor agonists 1, 2.
The primary ocular effects of benzodiazepines involve disturbances in eye movements (such as nystagmus and impaired tracking), not pupillary changes 3.
When evaluating a patient with dilated pupils, benzodiazepines should not be on your differential diagnosis for the cause of mydriasis 3, 4.
What Actually Causes Dilated Pupils
Anticholinergic drugs (including antihistamines, tricyclic antidepressants, and atropine-like substances) are the primary pharmacologic causes of mydriasis 1, 4, 5.
Sympathomimetic agents such as cocaine, amphetamines, and methylphenidate cause pupillary dilation through adrenergic stimulation 5.
Topical contamination with parasympatholytic agents, antihistamines, or plant alkaloids (Datura species containing atropine/scopolamine) can produce unilateral or bilateral mydriasis 4.
Clinical Pitfalls to Avoid
Do not attribute dilated pupils to benzodiazepine use in a patient presenting with altered mental status—this finding suggests a different drug class or pathology 3, 4.
Anticholinergics specifically cause blurred vision, dry mouth, dilated pupils, urinary retention, and sedation—a constellation of findings distinct from benzodiazepine effects 1.
If a patient on benzodiazepines presents with dilated pupils, consider co-ingestion with anticholinergic or sympathomimetic drugs, or an alternative diagnosis such as structural neurologic injury 4, 6.
What Benzodiazepines Actually Do to the Eyes
The documented ocular effects of benzodiazepines include impaired eye movements, nystagmus, and reduced ability to discriminate contrast (particularly with lorazepam) 3.
Benzodiazepines cause central nervous system depression manifesting as sedation, respiratory depression, and hypotension—not pupillary changes 1, 2.
In elderly patients, benzodiazepines increase risk of falls and cognitive impairment but do not alter pupil size 2.