Diagnostic Criteria for Allergic Conjunctivitis
Allergic conjunctivitis is diagnosed clinically based on history and physical examination findings, with ocular itching being the cardinal symptom that distinguishes it from other forms of conjunctivitis. 1, 2
Clinical History
The diagnosis relies primarily on identifying characteristic symptoms and temporal patterns:
- Ocular itching is the hallmark symptom that must be present and is the most specific feature differentiating allergic from infectious conjunctivitis 3, 4
- Tearing (epiphora) and redness are common accompanying symptoms 3, 2
- Photophobia may occur during acute phases 3
- Seasonal pattern suggests seasonal allergic conjunctivitis (SAC), with symptoms correlating to regional spring and fall allergen spikes 5
- Year-round symptoms indicate perennial allergic conjunctivitis (PAC), often triggered by indoor allergens like animal dander, dust mites, or cosmetics 4
- History of exposure to known allergens (airborne allergens, topical/systemic drugs, cosmetics, animal hairs) supports the diagnosis 4
Physical Examination Findings
Key clinical signs to identify on examination:
- Chemosis (conjunctival edema) is the leading clinical sign 4
- Conjunctival redness and hyperemia 2
- Lid edema 3
- The classic presentation is the "red eye" appearance 4
Diagnostic Testing
Laboratory testing is rarely necessary as the diagnosis is clinical 2:
- Diagnostic procedures are reserved for atypical presentations or when the diagnosis is uncertain 2
- The diagnosis can be made confidently based on thorough history and careful examination alone 1
Disease Classification
Once diagnosed, subclassify based on severity and chronicity:
- Acute forms: SAC and PAC comprise the vast majority of cases 5
- Chronic severe forms: Vernal keratoconjunctivitis, atopic keratoconjunctivitis, and giant papillary conjunctivitis require ophthalmology co-management 5, 3
- Chronic cases may show late-phase responses with eosinophilia and neutrophilia, and can lead to ocular surface tissue remodeling 3
Key Diagnostic Pitfall
The critical distinction is recognizing that allergic conjunctivitis is IgE-mediated type 1 hypersensitivity with mast cell-driven inflammation, differentiating it from infectious conjunctivitis which requires different management 3, 2. The presence of itching is the most reliable clinical feature to make this distinction 4.