I had a pt just now - normal neuro exam except for fixed dilated right pupil. sudden onset today. conj swollen, vision mostly normal???

Mydriasis: Mydriasis is a vexing problem for clinicians. It has many causes. You seem to be describing a condition known as Adie's pupil. This is an efferent pupillary defect that has many causes. The most common cause is viral infection of the ciliary ganglion. it may also be due to 3rd nerve compression, but I would expect other symptoms. Are eye pressures normal? Acute narrow angle glaucoma?

Pharmacological: exposure to the eye to an anticholinergic substance is the most likely cause. (pt got a chemical in the eye). A totally fixed pupil in a patient with no other neuor signs is likely that

Concerning: This is concerning. I would send her to the ER or ophthalmology for a slit-lamp exam, particularly regarding the conjunctiva. Not sure what would be causing this with normal vision and fixed dilated pupil.

Considerations: Did the patient use eyedrops or get splashed in face by a chemical? Is there any possibility of an Adie-Holmes pupil? (? absent reflexes) But my main concern would be a posterior cerebral artery Berry Aneurysm, and if that is ruled out, might consider diabetic complication.

Other sources?: While pharmacologic accident is most common , particularly in face of conjunctival irritation ,other sources for unilateral mydriasis include Lyme disease, neurosyphilis, acute unilateral glaucoma, acute third nerve palsy, contamination from botanical sources, and benign recurrent mydriasis. Urgent ophthalmologic consultation is in order if it does not resolve promptly.