Conjunctivitis - allergic
Exam Tips
- In OSCEs, bilateral itch is the key discriminator: if itch is absent, actively reconsider the diagnosis.
- Always document visual acuity in any red-eye station before treatment decisions.
- Red flags needing same-day ophthalmology: reduced vision, marked pain or photophobia, unilateral severe red eye, corneal signs, trauma/chemical injury, contact lens wearer with pain/photophobia, or suspected herpes.
- VKC pattern recognition scores marks: giant superior tarsal papillae and limbal Trantas dots (see Figure from page X in your ophthalmology atlas).
- Differentiate papillae (allergic/contact lens) from follicles (often viral/chlamydial) on lid eversion.
- State steroid safety explicitly in viva answers: specialist-only short courses with IOP/cataract risk monitoring and infection exclusion.
Definition
Allergic conjunctivitis is an IgE-mediated inflammatory disorder of the conjunctiva triggered by environmental allergens, producing a typically bilateral itchy red eye with watery or mucoid discharge. It includes seasonal and perennial forms, and more severe chronic phenotypes such as vernal keratoconjunctivitis (VKC) and atopic keratoconjunctivitis (AKC), which can involve the cornea and threaten vision if not managed promptly.
Pathophysiology
In sensitized individuals, allergen exposure cross-links allergen-specific IgE on conjunctival mast cells, causing immediate degranulation and release of histamine, tryptase, leukotrienes, and prostaglandins. Histamine (mainly via H1 receptors) drives the hallmark itch, while vascular mediator effects produce conjunctival hyperaemia, chemosis, and eyelid oedema. A late inflammatory phase with eosinophils, Th2 cytokines (e. g, IL-4/IL-5/IL-13), and epithelial surface dysfunction contributes to persistent symptoms; this chronic immune activity is particularly important in VKC/AKC where papillary hypertrophy, mucus hypersecretion, and corneal damage can occur.
Risk Factors
- Personal or family history of atopy (allergic rhinitis, asthma, atopic eczema)
- Seasonal aeroallergen exposure (tree/grass pollens), especially spring and early summer
- Perennial indoor allergens (house dust mite, mould spores, animal dander)
- Contact lens wear, poor lens hygiene, prolonged wear, or solution sensitivity (risk of giant papillary conjunctivitis)
- Hot arid climate and male sex in childhood/adolescence (higher risk of VKC)
- Coexisting ocular surface disease (blepharitis, dry eye) or reduced tear film/barrier function
Clinical Features
Symptoms
- Itching (cardinal symptom; usually bilateral, may be described as burning/stinging)
- Watery tearing or stringy/ropey mucoid discharge
- Redness and ocular irritation
- Eyelid swelling or peri-orbital puffiness in more severe episodes
- Fluctuation with allergen exposure, season, geography, or indoor environment
- Associated nasal allergy symptoms (sneezing, rhinorrhoea, nasal itch/congestion)
Signs
- Conjunctival injection (hyperaemia)
- Chemosis (bulbar/tarsal conjunctival oedema)
- Papillary reaction on tarsal conjunctiva (larger papillae in contact-lens related disease)
- Eyelid oedema
- VKC signs: giant superior tarsal papillae, limbal Horner-Trantas dots, possible pseudomembranes
- AKC signs: chronic periocular eczema changes, conjunctival scarring; corneal involvement in severe disease
Investigations
Management
Lifestyle Modifications
- Allergen avoidance where feasible: close windows in high pollen periods, sunglasses outdoors, shower/hair wash after outdoor exposure, reduce indoor dust mite/mould burden, keep pets out of bedroom
- Cold compresses and preservative-free lubricating drops to reduce itch and wash out allergens
- Avoid eye rubbing (worsens mast-cell degranulation and ocular surface injury)
- Stop contact lens wear during active inflammation; restart only when symptoms/signs settle and lens hygiene is optimized
- Treat coexisting rhinitis/atopy to reduce overall allergic load
Pharmacological Treatment
Topical mast-cell stabiliser / dual-acting antihistamine drops (first-line)
- Sodium cromoglicate 2% eye drops: 1-2 drops in each affected eye four times daily
- Nedocromil sodium 2% eye drops: 1 drop twice daily
- Olopatadine 0.1% eye drops: 1 drop twice daily
- Ketotifen 0.025% eye drops: 1 drop twice daily
Dual-acting agents give faster symptom relief than pure stabilisers; continue during exposure season for prevention. Remove contact lenses before instillation; avoid wearing lenses if eye is actively inflamed. Preservative-containing drops may irritate ocular surface in frequent use.
Oral non-sedating antihistamines (if concomitant rhinitis or persistent itch)
- Cetirizine 10 mg orally once daily
- Loratadine 10 mg orally once daily
- Fexofenadine 120 mg orally once daily (seasonal allergic rhinitis-associated symptoms)
Useful when ocular symptoms coexist with nasal allergy. Warn about possible mild sedation (especially cetirizine in some patients) and anticholinergic dryness effects that may worsen dry-eye symptoms in susceptible people.
Topical corticosteroids (specialist-supervised short courses for severe VKC/AKC)
- Fluorometholone 0.1% eye drops: typically 1 drop 2-4 times daily short term, then taper under ophthalmology guidance
- Dexamethasone 0.1% eye drops: specialist use only with close monitoring
Safety-critical: avoid/very cautious if active ocular infection (especially herpetic epithelial keratitis, fungal, or untreated bacterial disease). Risks include raised intraocular pressure, glaucoma, cataract, delayed corneal healing, and secondary infection; monitor IOP if repeated/prolonged use.
Topical calcineurin inhibitor-sparing immunomodulation (specialist care in refractory VKC/AKC)
- Ciclosporin eye drops (specialist protocols; concentration/frequency vary by product and service)
Used to reduce steroid burden in chronic severe allergic keratoconjunctivitis; transient stinging is common. Initiation and follow-up should be in ophthalmology.
Complications
- Reduced quality of life, irritability, poor concentration, and reduced school/work productivity
- Contact lens intolerance and giant papillary conjunctivitis
- Corneal epithelial disease, neovascularization, thinning, ulceration, and secondary infection in severe VKC/AKC
- Conjunctival scarring and chronic ocular surface disease (including severe dry eye)
- Cataract and glaucoma risk in severe disease and/or with repeated corticosteroid exposure
- Permanent visual impairment in advanced keratoconjunctivitis
Prognosis
Seasonal and perennial allergic conjunctivitis usually respond well to trigger control and topical therapy, although recurrences are common during ongoing allergen exposure. VKC often improves and may remit after puberty, whereas AKC tends to be chronic over years with higher risk of corneal morbidity. Prognosis is best when red flags are identified early and severe disease is co-managed with ophthalmology.
Sources & References
🏥BMJ Best Practice(1)
💊BNF Drug References(7)
- Antazoline with xylometazoline[management.pharmacological]
- Azelastine hydrochloride[management.pharmacological]
- Epinastine hydrochloride[management.pharmacological]
- Ketotifen[management.pharmacological]
- Lodoxamide[management.pharmacological]
- Olopatadine[management.pharmacological]
- Sodium cromoglicate[management.pharmacological]
✅NICE Guidelines(1)
- Conjunctivitis - allergic[overview]
📖Textbook References(5)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1824, 1825)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1094, 1095)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 579)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1094, 1095)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 646)[context]