Mast cell activation syndrome-related unusual periocular inflammation associated with mydriatic eyedrops during cataract surgery.

Purpose: Mast Cell Activation Syndrome (MCAS) is a condition characterized by the inappropriate and unpredictable activation of mast cells, resulting in episodic symptoms affecting various parts of the body. Cutaneous, gastrointestinal, respiratory, and cardiovascular symptoms are often reported and well characterized in MCAS. However, ocular manifestations associated with this condition are not frequently explored. Observations: This case report describes an unusual periocular inflammatory reaction in a 76-year-old male with a history of MCAS following uneventful cataract surgery, specifically triggered by procedural mydriatic eyedrops (tropicamide). The patient, diagnosed with MCAS based on symptoms, elevated tryptase, and adequate response to therapies, presented to ophthalmology clinic with pre-existing dry eye disease and blepharitis for blurred vision. Despite prophylactic treatment with oral and intravenous (IV) antihistamines, intraoperative subconjunctival dexamethasone, and postoperative anti-inflammatory medications, the patient developed periocular swelling and erythema, on the first postoperative day, following uneventful cataract surgery during which intraprocedural tropicamide was administered for dilation. Importantly, the reaction may have been triggered not by tropicamide itself but by one or more excipients (e.g., benzalkonium chloride) known to induce mast cell activation in susceptible individuals. Conclusions and importance: This unusual presentation, previously not well described in the context of MCAS, highlights the critical need for ophthalmologists to recognize the heightened risk of severe periocular inflammation in MCAS patients undergoing procedures involving routine mydriatic agents. The case underscores that such reactions may be excipient-driven rather than drug-specific, emphasizes the complex interplay between MCAS, ocular surface conditions, and ophthalmic medications, and necessitates increased awareness among healthcare providers to tailor management to prevent potentially severe outcomes.