What are the possible causes and treatments for a single red watery eye?

Single Red Watery Eye: Differential Diagnosis and Management

Immediate Assessment for Red Flags

Any single red eye with pain, vision loss, corneal opacity, severe purulent discharge, or photophobia requires same-day ophthalmology referral or emergency department evaluation. 1, 2

Critical Red Flags Requiring Urgent Ophthalmology Consultation (within 24 hours):

• Visual loss or decreased visual acuity 1, 2
• Moderate to severe ocular pain (beyond mild irritation or foreign body sensation) 1, 2
• Photophobia (intolerance to light) 1, 3
• Corneal involvement (loss of corneal transparency, visible opacity, or fluorescein uptake) 1, 2
• Severe purulent discharge (particularly if copious) 1, 2
• History of herpes simplex virus eye disease 1, 2
• History of immunocompromise 1
• Recent ocular surgery or trauma 1, 4

Key Diagnostic Considerations for Unilateral Presentation

Unilateral red eye should prompt consideration of causes beyond typical bilateral conjunctivitis, including corneal pathology, anterior uveitis, acute angle-closure glaucoma, or herpes simplex virus infection. 2, 4

Viral Conjunctivitis (Most Common Overall Cause):

• Typically starts unilaterally but frequently becomes sequentially bilateral within days 2
• Watery discharge with follicular reaction on inferior tarsal conjunctiva 2
• Preauricular lymphadenopathy (especially with adenovirus) 2
• Often accompanied by upper respiratory infection symptoms 2
• Self-limited, resolving in 5-14 days 2, 5

Bacterial Conjunctivitis:

• Can present unilaterally or bilaterally 2
• Mucopurulent discharge with matted eyelids upon waking 2, 5
• Papillary (not follicular) conjunctival reaction 2
• Preauricular lymphadenopathy less common unless hypervirulent organism 2

Herpes Simplex Virus (HSV) Conjunctivitis:

• Usually presents unilaterally (bilateral in atopic, pediatric, or immunocompromised patients) 2
• Vesicular rash or ulceration of eyelids 2
• Dendritic epithelial keratitis of cornea (requires slit-lamp examination) 2
• Requires immediate ophthalmology referral 1

Other Important Unilateral Causes:

• Corneal abrasion or foreign body (history of trauma, severe pain relieved by topical anesthetic) 4
• Acute anterior uveitis/iritis (deep eye pain, photophobia, ciliary flush) 4, 3
• Acute angle-closure glaucoma (severe pain, halos around lights, mid-dilated fixed pupil, corneal edema) 4, 3
• Subconjunctival hemorrhage (bright red blood, painless, no discharge) 4

Management Algorithm for Non-Emergent Cases

If No Red Flags Present and Suspected Viral Conjunctivitis:

Viral conjunctivitis does not respond to antibacterial agents and should not be treated with antibiotics. 2

• Supportive care with preservative-free artificial tears 4 times daily 2
• Cold compresses for symptomatic relief 2
• Topical antihistamines may provide symptomatic relief 2
• Patient education about high contagiousness for 10-14 days from symptom onset 2
• Strict hand hygiene, avoid sharing towels/pillows, avoid touching eyes 2
• Return if symptoms worsen, persist beyond 2-3 weeks, or red flags develop 2

If Suspected Bacterial Conjunctivitis (Mucopurulent Discharge, Matted Lids):

Mild bacterial conjunctivitis is self-limited, but moderate to severe cases benefit from a 5-7 day course of broad-spectrum topical antibiotic. 2

• Broad-spectrum topical antibiotic (e.g., moxifloxacin 0.5% one drop 3 times daily for 7 days) 6
• No specific antibiotic has proven superiority; choose based on convenience and cost 2
• Return in 3-4 days if no improvement 1
• Consider culture if recalcitrant or severe 1

Special Considerations:

Gonococcal conjunctivitis requires systemic treatment in addition to topical therapy due to risk of corneal perforation. 2

Chlamydial conjunctivitis requires systemic treatment and evaluation/treatment of sexual partners. 1, 2

Common Pitfalls to Avoid

• Do not use topical corticosteroids without ophthalmology consultation (can worsen HSV infections, prolong viral shedding, increase intraocular pressure, and cause cataracts) 2
• Do not prescribe antibiotics indiscriminately for viral conjunctivitis (provides no benefit and may cause toxicity) 2
• Do not allow contact lens wear during any infectious conjunctivitis 2
• Do not miss unilateral red eye with pain as potential sight-threatening emergency 4, 3
• Chronic or recalcitrant conjunctivitis may indicate underlying malignancy (sebaceous or squamous cell carcinoma) and requires further evaluation 2

When to Refer

Refer to ophthalmology for: lack of response to therapy after 3-4 days, recurrent episodes, conjunctival scarring, corneal involvement, or any red flag features. 1, 2