Allergic Conjunctivitis
IgE-mediated bilateral ocular itching, redness, and watery discharge — frequently with allergic rhinitis.
Also known as: allergic conjunctivitis, seasonal allergic conjunctivitis, perennial allergic conjunctivitis, vernal keratoconjunctivitis, atopic keratoconjunctivitis
Overview
Bilateral IgE-mediated inflammation of the conjunctiva caused by environmental allergens. Forms: seasonal (SAC, pollen) and perennial (PAC, dust mite/animal/mold) — most common; vernal keratoconjunctivitis (VKC) — pediatric, atopic, severe with corneal involvement; atopic keratoconjunctivitis (AKC) — adult, chronic, sight-threatening; giant papillary conjunctivitis (GPC) — related to contact lenses or ocular prostheses.
Epidemiology
Affects 15-40% of the population in some form. Often coexists with allergic rhinitis, asthma, and eczema. VKC is most common in male children 5-15 in warm climates; AKC affects adults with atopic dermatitis.
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Risk factors
- Personal or family history of atopy (asthma, eczema, food allergy, allergic rhinitis)
- Exposure to seasonal allergens (pollen) or year-round allergens (dust mite, mold, pet dander)
- Contact lens wear (GPC)
- Warm dry climate (VKC)
- Childhood (VKC)
Pathophysiology
Allergen exposure cross-links IgE bound to conjunctival mast cells, causing degranulation with histamine, tryptase, prostaglandins, and leukotrienes. Early phase: itching, tearing, redness within minutes. Late phase: eosinophil infiltrate hours later → chemosis and persistent symptoms. VKC and AKC have additional Th2-driven chronic inflammation with eosinophils.
Clinical presentation
Symptoms
- BILATERAL itching — the hallmark; 'I want to rub my eyes constantly'
- Watery or stringy mucoid discharge
- Redness, burning, foreign body sensation
- Eyelid swelling and chemosis
- Concurrent nasal symptoms (sneezing, congestion) — allergic rhinoconjunctivitis
- Triggered by pollens, animal dander, dust
Signs / physical exam
- Diffuse conjunctival hyperemia and chemosis (clear gelatinous swelling)
- Papillary reaction on tarsal conjunctiva (giant papillae in VKC, AKC, GPC)
- Watery or ropy mucus discharge
- Mild eyelid edema
- Allergic shiners
- VKC: limbal Horner-Trantas dots, shield ulcer on cornea — sight-threatening
- AKC: lichenified eyelid skin, keratoconus, cataracts in chronic disease
Classic findings
Bilateral itching with chemosis and watery stringy discharge in an atopic patient.
Differential diagnosis
- Viral conjunctivitis — Watery discharge, preauricular adenopathy, recent URI, follicular reaction; itching mild
- Bacterial conjunctivitis — Purulent discharge, eyelids matted shut, no itching
- Dry eye disease — Burning, foreign body sensation, worse end of day, fluorescein punctate staining, low tear film breakup time; artificial tears, cyclosporine
- Blepharitis — Eyelid margin scaling, telangiectasias, crusting; lid hygiene
- Contact dermatitis of eyelid — Erythema and scaling of lid skin, history of allergen exposure (cosmetics, drops); topical steroid to lid
- Toxic conjunctivitis — Recent topical drop or preservative exposure; resolves with cessation
- Giant papillary conjunctivitis (GPC) — Contact lens wearer with itching, mucus, large papillae on upper tarsus; lens hygiene change
Diagnostic workup
Labs
- Clinical diagnosis based on history and exam
- Allergy testing (skin prick or specific IgE) if persistent or trigger unclear
- Conjunctival scraping rarely needed — would show eosinophils
Imaging
- Slit-lamp examination for chemosis, papillae, and corneal involvement
- Fluorescein staining if corneal symptoms — exclude shield ulcer or punctate keratitis
Diagnostic algorithm
| Subtype | Population | Key Features | Risk |
|---|---|---|---|
| Seasonal allergic conjunctivitis (SAC) | Atopic, all ages | Pollen-triggered, itching, chemosis | Low — symptomatic |
| Perennial allergic conjunctivitis (PAC) | Year-round atopic | Dust mite/pet/mold-triggered | Low — symptomatic |
| Vernal keratoconjunctivitis (VKC) | Boys 5-15, warm climate | Cobblestone tarsal papillae, Horner-Trantas dots, shield ulcer | Sight-threatening (shield ulcer, keratoconus) |
| Atopic keratoconjunctivitis (AKC) | Adults with atopic dermatitis | Chronic, eyelid lichenification, corneal scarring | Sight-threatening; keratoconus, cataract |
| Giant papillary conjunctivitis (GPC) | Contact lens wearers | Itching, mucus, giant tarsal papillae | Lens intolerance |
Treatment
First-line
- Allergen avoidance — close windows during high pollen counts, wash hands and face after exposure, dust mite covers, pet dander measures
- Cold compresses to reduce itching and swelling
- Artificial tears (preservative-free preferred) to dilute and wash allergens
- Topical ophthalmic antihistamine/mast cell stabilizer — olopatadine 0.1-0.7%, ketotifen 0.025%, alcaftadine, bepotastine — combined agents are first-line for moderate-severe disease
- Topical mast cell stabilizer alone — cromolyn, lodoxamide, nedocromil — slower onset, useful prophylactically
- Oral 2nd-generation antihistamine (loratadine, cetirizine, fexofenadine) if concurrent allergic rhinitis
Second-line / adjunct
- Topical NSAIDs (ketorolac) — short-term symptom relief
- Topical corticosteroids — short course (1-2 weeks) under ophthalmologist supervision for severe acute flares; monitor IOP and cataract formation
- Topical calcineurin inhibitors (cyclosporine 0.05-0.1%, tacrolimus) — VKC/AKC and steroid-sparing chronic cases
- Allergen immunotherapy (SCIT or SLIT) — particularly when concurrent allergic rhinitis warrants disease modification
- Ophthalmology referral for VKC, AKC, shield ulcer, GPC unresponsive to lens change, or steroid dependence
Complications
- Chronic eye rubbing → keratoconus (especially in VKC/AKC)
- Corneal shield ulcer in VKC (sight-threatening)
- Cataract and glaucoma from chronic topical steroid use
- Secondary bacterial infection from rubbing
- Reduced quality of life, sleep disruption, school/work impairment
PANCE pearls
- BILATERAL ITCHING is the hallmark of allergic conjunctivitis — without itching, look elsewhere.
- Topical olopatadine (antihistamine + mast cell stabilizer) is the workhorse — once-daily 0.7% formulation has good efficacy.
- AVOID prolonged topical corticosteroids without ophthalmology supervision — cataract, glaucoma, and HSV reactivation risk.
- Topical decongestant drops (naphazoline, tetrahydrozoline) cause rebound hyperemia with chronic use — discourage.
- VKC and AKC are sight-threatening atopic phenotypes — refer to ophthalmology; treat eye rubbing to prevent keratoconus.
- Contact lens wearer with itching + mucus + giant papillae = giant papillary conjunctivitis — change lens type/material or discontinue.
References
- AAO 2018 — American Academy of Ophthalmology. Conjunctivitis Preferred Practice Pattern. Ophthalmology 2019;126(1):P94-P169
- AAAAI 2020 — Bielory L et al. ICON: Diagnosis and Management of Allergic Conjunctivitis. Ann Allergy Asthma Immunol 2020;124(2):118-134
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