Understanding Pupil Dilation Issues: Causes & Potential Solutions

Impaired pupillary dilation (mydriasis failure) has diverse causes.

Medications (Common)

• Anticholinergics (atropine, scopolamine) → dilation (opposite effect)
• Opioids, clonidine, alpha-2 agonists → constriction (miosis)
• Antihistamines, antidepressants (TCAs), antipsychotics → anticholinergic effects (dilation) or variable
• Pilocarpine, cholinesterase inhibitors → constriction

Neurological

• Horner's Syndrome: Ptosis, miosis, anhidrosis (sympathetic deficit).
• CN III Palsy: Dilated, fixed pupil (parasympathetic loss) + ptosis, eye down/out.
• Adie's Tonic Pupil: Dilated, slow constriction to light/near.
• Brainstem stroke, tumor, aneurysm (posterior communicating).

Ocular

• Uveitis (posterior synechiae)
• Angle-closure glaucoma
• Trauma (sphincter tear)
• Prior intraocular surgery

Systemic

• Diabetic autonomic neuropathy
• Autonomic dysreflexia

Congenital

Aniridia, corectopia.

Evaluation

Pupillometry, swinging flashlight test (RAPD), slit lamp, neuroimaging (MRI/MRA) if neurological signs. Urgent if acute CN III palsy (aneurysm risk).