Allergic Conjunctivitis

Allergic conjunctivitis is an IgE-mediated type I hypersensitivity reaction of the conjunctiva.

• Seasonal allergic conjunctivitis (pollens, grasses, trees) and perennial (dust mite, animal dander, mould) are the commonest types, affecting up to 40 percent of the population.
• Frequently associated with allergic rhinitis, asthma, and eczema (atopic triad).
• Mast cell degranulation releases histamine, tryptase and leukotrienes in minutes; a late phase brings eosinophils and Th2 cells.
• Other forms: vernal and atopic keratoconjunctivitis (sight threatening), giant papillary conjunctivitis, contact allergic (drops, preservatives).

• Intense itching (the hallmark), watery or ropy discharge, burning, tearing, bilateral symptoms.
• Conjunctival injection (pink rather than red), chemosis, lid oedema, papillae (fine), periorbital dark circles ("allergic shiners").
• Cornea is normal; vision unaffected.
• Association with sneezing, nasal congestion and a clear seasonal pattern.
• Contact dermatitis from drops: eczematous eyelid skin with scaling and papillary conjunctivitis.

• Clinical history of itch with seasonal or perennial pattern and atopy.
• Conjunctival scraping showing eosinophils is supportive but rarely needed.
• Skin prick testing or serum specific IgE to identify allergens for persistent disease.
• Exclude infection, dry eye, and blepharitis; look for a corneal shield ulcer or limbal papillae suggesting vernal disease.

• Allergen avoidance: closed windows during pollen season, wash bedding at 60 degrees, dust mite covers, remove pets from bedrooms, avoid rubbing, wear sunglasses.
• Cold compresses and preservative free artificial tears to dilute allergens.
• First line: dual action topical antihistamine and mast cell stabiliser: olopatadine 0.1 percent twice daily or 0.2 percent once daily, ketotifen 0.025 percent twice daily, azelastine 0.05 percent twice daily, bepotastine 1.5 percent twice daily, alcaftadine 0.25 percent once daily, epinastine 0.05 percent twice daily.
• Mast cell stabilisers: sodium cromoglicate 2 percent four times daily, lodoxamide 0.1 percent four times daily (loading period of 1 to 2 weeks, best used prophylactically).
• Oral antihistamines: cetirizine 10 mg once daily or loratadine 10 mg once daily (may worsen dry eye).
• Short course of low potency steroid for severe flares: loteprednol 0.2 or 0.5 percent or fluorometholone 0.1 percent four times daily for 1 to 2 weeks. Avoid prolonged steroids (cataract, glaucoma).
• Immunotherapy (subcutaneous or sublingual) for persistent allergic rhinoconjunctivitis.
• Avoid vasoconstrictor drops (rebound hyperaemia).