Clonazepam Does Not Cause Mid-Dilated Pupils
Clonazepam and other benzodiazepines do not cause pupillary dilation or mid-dilated pupils; in fact, benzodiazepines have no significant effect on pupil size despite causing sedation. 1
Evidence Against Pupillary Effects
A controlled study specifically examining diazepam (a benzodiazepine like clonazepam) demonstrated that despite causing clear sedation (measured by reduced alertness scores and critical flicker fusion frequency), the drug had no effect on pupil diameter, light reflexes, or darkness reflexes 1
This study used pharmacological manipulation with both sympatholytic (dapiprazole) and parasympatholytic (tropicamide) agents to test whether benzodiazepines might be masking pupillary changes by affecting both sympathetic and parasympathetic pathways—the results showed benzodiazepines do not attenuate either sympathetic or parasympathetic outflow to the iris 1
The paradoxical finding that benzodiazepine-induced sedation is not accompanied by the expected miosis (pupil constriction) that typically occurs with decreased arousal has been well-documented 1
Clinical Context: When Mid-Dilated Pupils Matter
Mid-dilated pupils are clinically significant in specific ophthalmologic contexts:
In acute angle-closure crisis, a mid-dilated pupil is a cardinal sign along with corneal edema, conjunctival injection, elevated intraocular pressure, and eye pain 2
In opioid overdose assessment, miosis (constricted pupils, not mid-dilated) is strongly correlated with opioid toxicity and response to naloxone, though many factors affect pupil size 2
In neurological monitoring, automated pupillometry assesses pupil size and reactivity for prognostication, but high opiate doses (not benzodiazepines) may affect reliability 2
Important Caveat
If a patient taking clonazepam presents with mid-dilated pupils, look for alternative causes rather than attributing this finding to the medication—consider tricyclic antidepressants, typical antipsychotics, SSRIs (which can cause mydriasis), topiramate, or underlying ophthalmologic conditions like angle-closure glaucoma 3