Nummular keratitis: A rare manifestation of brimonidine allergy.

A 32-year-old male, with juvenile open-angle glaucoma on chronic antiglaucoma therapy and recently introduced brimonidine eye drops to the treatment regimen, developed bilateral follicular conjunctivitis with subepithelial infiltrates (SEIs) initially resembling common infectious keratoconjunctivitis entities. The persistent nature of the conjunctivitis, the lack of positive conjunctival cultures, the absence of systemic symptoms, the full resolution of the condition upon discontinuation of antiglaucoma drops, and the commencement of topical steroids, along with the reappearance of SEIs upon reintroducing brimonidine; suggested an immune-mediated drug reaction secondary to a Benzalkonium chloride (BAK) preserved brimonidine tartrate 0.2% formulation. The interval between the initiation of brimonidine and the onset of the drug reaction was 13 months and shortened to 1 week upon re-exposure to the drug. The condition fully resolved without further sequelae off brimonidine. Brimonidine is notoriously known for causing ocular allergic reactions, the most common being follicular conjunctivitis, but very few reports exist describing its adverse effects on the cornea. This case highlights that brimonidine may directly or indirectly induce an immune reaction affecting the cornea in the form of SEIs. Brimonidine is, thus, capable of mimicking more commonly recognized infectious disease entities causing keratoconjunctivitis. This is the second report of a similar manifestation linked to its use.