What is the most likely diagnosis and first‑line management for a 2‑year‑old presenting with itchy, watery eyes without purulent discharge, fever, pre‑auricular lymphadenopathy, or photophobia?

Allergic Conjunctivitis: Diagnosis and First-Line Management in a 2-Year-Old

The most likely diagnosis is allergic conjunctivitis, and first-line management consists of topical antihistamine/mast cell stabilizer combination drops (olopatadine) plus cool compresses and artificial tears. 1, 2

Clinical Reasoning

The presentation of itchy, watery eyes without purulent discharge, fever, preauricular lymphadenopathy, or photophobia strongly points away from infectious etiologies and toward allergic conjunctivitis. 2, 3, 4

Key Diagnostic Features Supporting Allergic Conjunctivitis:

• Itching is the hallmark symptom that distinguishes allergic from infectious conjunctivitis—viral and bacterial causes produce irritation or grittiness, not true pruritus. 5, 4
• Watery (not purulent) discharge rules out bacterial conjunctivitis, which presents with mucopurulent discharge and matted eyelids. 3, 4
• Absence of fever and preauricular lymphadenopathy makes viral conjunctivitis (especially adenoviral) unlikely, as these typically present with systemic symptoms and lymph node enlargement. 2, 6
• No photophobia excludes corneal involvement seen in more severe conditions like vernal keratoconjunctivitis. 1, 7

What to Look For on Examination:

• Bilateral presentation is typical for allergic conjunctivitis (seasonal or perennial). 5, 8
• Conjunctival injection with a pale, boggy appearance rather than bright red. 6
• Dark infraorbital circles (allergic facies) and horizontal lower eyelid folds (Morgan-Dennie lines) support chronic allergic disease. 6
• Clear, watery discharge (may appear pale yellow if inflammation is severe). 6
• Absence of follicular reaction on tarsal conjunctiva—follicles suggest viral or chlamydial causes. 1, 2

First-Line Treatment Algorithm

Step 1: Non-Pharmacological Measures (Always Start Here)

• Cool compresses provide immediate symptomatic relief. 2, 4
• Artificial tears/ocular lubricants dilute allergens and stabilize the tear film. 1, 5, 4
• Allergen avoidance when triggers are identified (dust mites, pollen, pet dander). 1, 5

Step 2: Topical Antihistamine/Mast Cell Stabilizer (First-Line Pharmacotherapy)

Olopatadine 0.1% ophthalmic solution is FDA-approved for children ≥2 years old: 1 drop in affected eye(s) twice daily, every 6-8 hours, no more than twice per day. 9

• Dual-action agents (antihistamine + mast cell stabilizer) are preferred over single-action drops because they address both immediate and late-phase allergic responses. 5, 4
• Single-dose preservative-free formulations are ideal to minimize toxicity and hypersensitivity to preservatives. 5

Step 3: Systemic Antihistamines (Adjunctive Therapy)

• Oral antihistamines can be added if nasal symptoms coexist (allergic rhinoconjunctivitis) or if topical therapy alone is insufficient. 1, 5, 4

When to Escalate or Refer

Red Flags Requiring Ophthalmology Referral:

• Visual changes, moderate-to-severe pain, or photophobia suggest corneal involvement or more serious pathology. 2, 6
• Unilateral presentation raises concern for HSV, VZV, or other non-allergic causes. 2, 6
• Giant papillae on tarsal conjunctiva indicate vernal or atopic keratoconjunctivitis, which require specialist management with topical corticosteroids or cyclosporine. 1, 5
• No improvement after 3-4 days of first-line therapy warrants re-evaluation. 2

Severe Allergic Conjunctivitis (Vernal/Atopic Keratoconjunctivitis):

• Short-term topical corticosteroids are necessary for acute exacerbations but require ophthalmology supervision due to risks of glaucoma and cataracts. 1
• Topical cyclosporine 0.1% is FDA-approved for vernal keratoconjunctivitis and serves as a steroid-sparing agent. 1
• Tacrolimus 0.03% ointment (off-label) can be used for eyelid involvement in children ≥2 years old. 1

Critical Pitfalls to Avoid

• Do not prescribe topical corticosteroids without ophthalmology consultation in primary care—they can exacerbate herpetic infections and cause steroid-induced glaucoma or cataracts. 6
• Do not assume bilateral presentation excludes HSV—adenoviral conjunctivitis often starts unilaterally before becoming bilateral within days. 2, 6
• Always perform fluorescein staining if there is any doubt about the diagnosis to rule out corneal involvement (dendritic keratitis in HSV, corneal ulcers in bacterial infection). 2, 6
• Recognize that "no discharge" does not exclude infectious causes—early viral conjunctivitis may have minimal watery discharge. 6

Expected Outcome

• Seasonal allergic conjunctivitis typically improves within days of starting dual-action topical therapy. 5, 8
• Perennial allergic conjunctivitis (e.g., dust mite allergy) requires ongoing management and environmental control measures. 5, 8
• Chronic forms (vernal/atopic keratoconjunctivitis) can cause corneal scarring and vision loss if untreated, emphasizing the importance of specialist follow-up. 1, 7