This patient most likely has allergic conjunctivitis, which typically presents with eye redness, itching, and tearing, often in conjunction with allergy symptoms following allergen exposure. Eye findings are typically bilateral, and chemosis (conjunctival edema) and a watery, nonpurulent discharge are often seen on examination. Treatment of allergic conjunctivitis includes allergen avoidance and other nonpharmacologic interventions, such as cool topical compresses and artificial tears. Discontinuing contact lens use is also usually recommended for symptomatic patients. Pharmacologic treatment may include over-the-counter antihistamine/vasoconstrictor eye drops, oral antihistamines, or topical antihistamines (olopatadine ophthalmic 0.1%, ketotifen ophthalmic).

Bacterial conjunctivitis tends to be an acute process, commonly occurring in one eye. Patients frequently report redness, itching, and a mucopurulent discharge that causes crusting in the morning but also persists during the day. Bacterial conjunctivitis is commonly caused by infection with Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, or Moraxella catarrhalis. It tends to be very contagious, and treatment is topical antibiotics. This patient's watery eye discharge is not consistent with bacterial conjunctivitis.

Blepharitis is a diffuse inflammation of the sebaceous glands or lash follicles of the eyelids. Common causes are S. aureus infection, rosacea, and seborrheic dermatitis. This patient does not have evidence of seborrheic dermatitis, which, if present, would predispose her to blepharitis.

Viral conjunctivitis is usually an acute process associated with antecedent upper respiratory tract infection. It is commonly caused by one of several types of adenovirus and is often seen following exposure to infected persons. One eye is frequently involved, although the other eye may become involved following the first. Symptoms include itching, foreign body sensation, and a watery or mucoid discharge with crusting of the eyelids following sleep. Treatment is supportive, including cold compresses and artificial tears. This patient's symptoms and clinical course make viral conjunctivitis less likely.