Do pupils dilate during a seizure?

Pupillary Changes During Seizures

Pupils typically dilate during most seizures, though the specific pattern depends on seizure type and localization; miosis (pupillary constriction) is rare and usually indicates specific focal seizure activity.

Typical Pupillary Response

Generalized Tonic-Clonic Seizures

• Pupillary dilation is the common autonomic response during generalized tonic-clonic (grand mal) seizures, occurring as part of the widespread sympathetic activation that accompanies these events 1.
• The dilation reflects the intense autonomic discharge that characterizes the ictal period, similar to other sympathetic manifestations like tachycardia and hypertension 1.

Focal Seizures

• Motor and non-motor manifestations vary by seizure focus, but autonomic features including pupillary changes can occur depending on the cortical regions involved 2.
• Pupillary dilation is particularly common when seizures involve or spread to regions controlling autonomic function 2.

Atypical Pupillary Response: Seizure-Induced Miosis

Rare Presentation

• Ictal miosis (pupillary constriction) is distinctly uncommon but has been documented in specific focal seizure cases 3.
• When miosis occurs, it typically indicates focal seizures originating from specific cortical regions, such as the parietal cortex 3.

Clinical Significance

• A case report documented bilateral pupillary miosis during focal seizures secondary to cortical dysplasia in the left middle parietal gyrus, with seizure onset coincident with focal left centroparietal fast spike activity on EEG 3.
• This patient became seizure-free after complete resection of the cortical dysplasia, confirming the localization 3.

Physiological Mechanism

Autonomic Activation

• Pupillary dilation during seizures reflects psychological arousal and autonomic activation, similar to the pupillary response seen in fear conditioning paradigms 4.
• The pupillary response is fast and reflects a measure of psychological arousal, making it a useful marker of ictal autonomic changes 4.

Sympathetic Predominance

• The typical sympathetic surge during most seizures drives pupillary dilation through activation of the dilator pupillae muscle 4.
• Parasympathetic-mediated miosis during seizures suggests unusual seizure localization or propagation patterns 3.

Clinical Pitfalls

• Do not assume all seizures cause dilation: While dilation is typical, observing miosis should prompt consideration of focal seizures with specific cortical involvement 3.
• Pupillary examination timing matters: Assess pupils during the ictal period, as post-ictal changes may differ from ictal findings 3.
• Bilateral versus unilateral changes: Unilateral pupillary changes may provide lateralizing information about seizure focus, though bilateral changes are more common in generalized seizures 3.