Immunology and AllergyTier 1Disease (DEADMAN)

Allergic disorders - conjunctivitis

Description

IgE-mediated (Type I) hypersensitivity of the conjunctiva - seasonal (SAC) or perennial (PAC) allergic conjunctivitis are the common forms
Vernal and atopic keratoconjunctivitis are rarer, more severe, sight-threatening variants with a T-cell component

Very common, affects a large proportion of allergic rhinitis patients (frequently co-occurs - "rhinoconjunctivitis")
Vernal keratoconjunctivitis - young males, warmer climates, often resolves by adulthood
Atopic keratoconjunctivitis - adults with longstanding atopic dermatitis

Conjunctival mast cell degranulation on allergen (pollen, dust mite, animal dander) exposure -> histamine release -> itch, vasodilation, chemosis
Vernal/atopic keratoconjunctivitis - chronic Th2-driven inflammation with eosinophil involvement -> corneal complications (unlike simple SAC/PAC)

Clinical - largely distinguishes the forms

SAC/PAC: bilateral itch (the cardinal symptom), watery discharge, conjunctival injection/chemosis, associated rhinitis; no corneal involvement
Vernal keratoconjunctivitis: severe itch, thick mucoid discharge, giant papillae (cobblestoning) on upper tarsal conjunctiva, limbal (Horner-Trantas) dots, corneal shield ulcers if severe
Atopic keratoconjunctivitis: chronic, associated eyelid eczema, corneal scarring/vascularisation risk with longstanding disease

Key distinguishing feature from infective conjunctivitis

Bilateral, itch-predominant, watery/mucoid (not purulent) discharge in allergic disease vs unilateral onset with purulent discharge in bacterial conjunctivitis

SAC/PAC - stepwise

Cold compresses + preservative-free artificial tears - simple first measure
Topical dual-action antihistamine/mast cell stabiliser (e.g. olopatadine, ketotifen) - first-line pharmacotherapy
Topical mast cell stabiliser (sodium cromoglycate) - for prophylaxis before predictable exposure (season)
Oral antihistamine - adjunct, especially with concurrent rhinitis
Avoid topical decongestants (vasoconstrictors) long-term - rebound hyperaemia

Vernal/atopic keratoconjunctivitis - specialist co-management

Topical corticosteroid for significant inflammation/corneal involvement - short courses, ophthalmology-supervised (cataract/glaucoma risk with prolonged use)
Topical ciclosporin/tacrolimus - steroid-sparing for chronic disease
Urgent ophthalmology referral for corneal shield ulcers or visual threat

Allergic rhinitis (very frequently co-existing), atopic dermatitis, asthma
Vernal/atopic keratoconjunctivitis - corneal scarring, keratoconus (from chronic eye rubbing), visual impairment if untreated

SAC/PAC - benign, symptom-driven, no long-term ocular damage
Vernal keratoconjunctivitis - typically improves/resolves around puberty
Atopic keratoconjunctivitis - chronic, can cause progressive corneal damage and visual loss if inadequately controlled - needs ongoing specialist follow-up

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