Case Presentation: Acute anisocoria prompts urgent evaluation due to the risk of intracranial hemorrhage, aneurysmal compression of CN III, or ischemic stroke. However, pharmacologic and toxic causes of unilateral mydriasis can mimic these emergencies. Household cleaning agents, particularly those containing quaternary ammonium compounds, may cause pupillary dilation through inadvertent ocular exposure. This case demonstrates how a benign, reversible condition triggered a stroke alert and highlights the diagnostic value of environmental exposure history. A 36-year-old woman with no significant past medical history aside from infrequent migraines presented with sudden left-sided blurry vision and a mild bilateral frontal headache while cleaning a residential property. She denied trauma, ocular pain, weakness, or sensory symptoms. In the emergency department, she was alert and oriented with isolated left mydriasis (5 mm vs 2 mm on the right) with sluggish reactivity, intact extraocular movements, preserved visual fields, and no focal neurologic deficits (NIHSS 2). A stroke alert was activated. CT head and CT angiography of the head and neck revealed no acute intracranial abnormalities, vascular occlusion, or aneurysm. Laboratory studies and chest radiograph were normal. Neurology recommended MRI brain for further evaluation of anisocoria. TTE was also ordered for stroke workup. By the next morning, the patient’s symptoms had resolved completely, and her neurologic exam was normal. On detailed history, she reported prolonged exposure to multiple open buckets of Pine-Sol while cleaning, with strong fumes and no glove use. Given rapid resolution, normal imaging, and this discovered source of exposure after extensive history taking, this was most consistent with transient pharmacologic mydriasis. The MRI brain and TTE were not pursued for these reasons, and patient was discharged with follow up instructions.
Discussion: Anisocoria is a high-risk finding, necessitating immediate evaluation to exclude life-threatening causes. However, stroke mimics are common and may lead to extensive diagnostic workup. Chemical-induced pharmacologic mydriasis is underrecognized, particularly in non–healthcare occupational settings. A few components of Pine Sol, 1-alpha-terpineol and d-limonene, are both volatile organic compounds known to have significant chemesthetic impacts. While not commonly reported, agents such as Pine-Sol can cause unilateral pupillary dilation when transferred to the eye directly or via contaminated hands.Several features in this case support a benign etiology: isolated mydriasis without ophthalmoplegia, normal neuroimaging, absence of systemic neurologic deficits, rapid spontaneous resolution, and identification of a credible exposure source. Incorporating environmental and occupational history early in the diagnostic process can reduce unnecessary imaging, limit hospital admissions, and improve diagnostic accuracy. This is especially critical in young, otherwise healthy patients who present with isolated visual symptoms.
Conclusions: This case illustrates how accidental exposure to household cleaning agents can cause transient unilateral mydriasis that mimics serious neurologic pathology. A targeted exposure history is essential in evaluating anisocoria and can help differentiate benign toxic or pharmacologic causes from neurologic emergencies. Early recognition of stroke mimics improves resource utilization while maintaining patient safety.