Clinical Signs of Allergic Conjunctivitis
Allergic conjunctivitis characteristically presents with bilateral eyelid edema, conjunctival injection, chemosis, watery discharge, and a papillary reaction on the palpebral conjunctiva, with itching being the hallmark symptom that distinguishes it from other forms of conjunctivitis. 1
Cardinal Clinical Signs
Ocular Surface Findings
- Bilateral presentation is the rule, affecting both eyes simultaneously 1
- Conjunctival injection (redness) of the bulbar conjunctiva is prominent 1
- Chemosis (conjunctival swelling/edema) develops due to vascular permeability 1
- Papillary reaction on the palpebral (tarsal) conjunctiva, particularly visible when everting the eyelid 1
- Watery discharge is typical, though mild mucous discharge may also occur 1
Periocular Manifestations
- Eyelid edema (swelling of the lids) is a consistent finding 1
- Periorbital hyperpigmentation ("allergic shiners") appears as dark circles under the eyes from chronic venous congestion 1
Distinguishing Features by Subtype
Seasonal/Perennial Allergic Conjunctivitis:
- Recurrent episodes correlating with allergen exposure (pollens, grasses for seasonal; dust mites, pet dander for perennial) 1
- Often associated with allergic rhinitis, dry eye, and meibomian gland dysfunction with mucin hyperproduction 1
- Minimal long-term sequelae 1
Vernal Keratoconjunctivitis (severe childhood form):
- Giant papillary hypertrophy of the superior tarsal conjunctiva (palpebral variant) 1
- Horner-Trantas dots at the limbus (collections of eosinophils and epithelial debris) 1
- Stringy mucoid discharge that is thick and ropy 1
- Limbal "papillae" and potential corneal involvement including epithelial erosions, neovascularization, and shield ulcers 1
- Bilateral presentation with onset in childhood, chronic course with spring/summer exacerbations 1
Key Symptom Profile
Itching is the pathognomonic symptom that most reliably indicates allergic etiology, typically affecting both eyes and often accompanied by tearing 1, 2
Additional symptoms include:
Associated Systemic Features
- Allergic rhinitis coexists in over 75% of patients with seasonal allergic conjunctivitis 1
- Environmental allergen exposure history (grasses, pollens, dust mites, pet dander) 1
- Climate factors including low latitude, high mean annual temperature, and low annual outdoor humidity increase risk 1
- Outdoor air pollution from fuel combustion, forest fires, and environmental tobacco smoke exposure 1
Critical Diagnostic Pitfalls
What Allergic Conjunctivitis Is NOT:
- Follicular reaction on the inferior tarsal conjunctiva suggests viral (not allergic) conjunctivitis 1, 4
- Unilateral presentation should prompt consideration of other diagnoses including HSV, bacterial infection, or foreign body 4, 5
- Purulent or mucopurulent discharge indicates bacterial rather than allergic etiology 4, 6
- Preauricular lymphadenopathy points toward viral conjunctivitis, not allergic 4
Red Flags Requiring Immediate Referral:
- Decreased vision 6
- Moderate-to-severe pain 5
- Corneal involvement on fluorescein staining 4, 5
- Photophobia 6
- Recent ocular surgery 6
Examination Technique
Always perform fluorescein staining to exclude corneal involvement, as this distinguishes simple allergic conjunctivitis from vision-threatening conditions 4, 5
Key examination steps:
- Assess bilaterality and symmetry of findings 1
- Evert the upper eyelid to visualize papillary reaction on tarsal conjunctiva 1
- Check for limbal involvement (Horner-Trantas dots in vernal disease) 1
- Document discharge character (watery vs. purulent) 1, 6
- Palpate for preauricular lymph nodes (their presence suggests viral, not allergic cause) 4
Natural History
Seasonal allergic conjunctivitis follows a recurrent pattern with acute exacerbations during pollen seasons, with symptoms declining as pollen counts fall (though may lag due to priming phenomenon) 1. Perennial disease persists year-round with fluctuating severity based on indoor allergen exposure 1. The condition is generally self-limited with minimal sequelae when properly managed 1.