Viral Conjunctivitis

Viral conjunctivitis, usually caused by adenovirus, is the most common infectious cause of a red eye in adults.^[1] It typically follows an upper respiratory tract infection and is highly contagious, especially in the first 3-7 days. The essential first task is not confirming a viral cause — it is confirming this is conjunctivitis at all and not a sight-threatening red-eye mimic (angle-closure glaucoma, iritis/uveitis, scleritis, keratitis, corneal ulcer), and not herpes simplex or herpes zoster ocular involvement, which — unlike adenoviral conjunctivitis — requires systemic antiviral treatment and ophthalmology co-management.^[2]

Typical (adenoviral) presentation

A very red eye with swollen lids, watery discharge, conjunctival membranes, and sometimes subconjunctival hemorrhage. Often follows or accompanies upper respiratory tract infection symptoms (cough, coryza, sore throat). Usually starts in one eye and spreads to the other within days. A preauricular lymph node is a helpful, though not universal, clue.

• Exposure to a person with a red eye or a recent upper respiratory tract infection.
• Community/institutional settings with close contact (schools, daycare, healthcare settings) — adenoviral conjunctivitis spreads easily via hand-to-eye contact and contaminated surfaces.
• History of herpes labialis or prior ocular herpes simplex, for recurrent herpetic keratoconjunctivitis.
• History of varicella/shingles risk factors (older age, immunocompromise) for herpes zoster ophthalmicus.

Differentiating bacterial, viral, and allergic conjunctivitis, and blepharitis

These four conditions are the most commonly confused causes of a red, irritated eye in community practice. Distinguishing them correctly determines whether the patient needs an antibiotic, supportive care, an antihistamine, or eyelid hygiene — and getting it wrong means either an unnecessary antibiotic or a missed diagnosis.

Bacterial conjunctivitis — purulent discharge with morning crusting. (CNX OpenStax, CC BY 4.0, Wikimedia Commons)

Viral conjunctivitis — marked redness, watery discharge, often with a preauricular node. (Joyhill09, CC BY-SA 3.0, Wikimedia Commons)

Allergic conjunctivitis — itching is the dominant symptom, often with chemosis (conjunctival swelling). (James Heilman, MD, CC BY-SA 4.0, Wikimedia Commons)

Blepharitis — crusting and scale at the lash base; this is an eyelid problem, not a conjunctival infection, though it can cause secondary conjunctivitis. (Imrankabirhossain, CC BY-SA 4.0, Wikimedia Commons)

History

• Unilateral or bilateral onset, duration, and progression — viral conjunctivitis classically starts in one eye and spreads.
• Preceding or concurrent upper respiratory tract infection symptoms.
• Exposure to a person with a red eye.
• History of cold sores or prior ocular herpes, or facial vesicles in a dermatomal distribution.

Examination

• Best corrected visual acuity (with pinhole if glasses are unavailable).
• Inspect lids, conjunctiva, sclera, and cornea; fluorescein staining if corneal involvement is possible — look specifically for a dendritic pattern suggesting herpes simplex.
• Palpate for preauricular lymphadenopathy.
• Examine the periorbital skin and, for suspected zoster, the full V1 dermatome and nose tip (Hutchinson's sign).

• Preserve eyesight and prevent structural (corneal) damage.
• Limit spread of infection to others.
• Provide symptomatic relief.

• Fastidious hand hygiene and avoiding eye touching — the single most effective way to limit spread.
• Use separate towels and pillowcases; avoid sharing eye makeup or contact lens supplies.
• Stay home from school/work for 3-7 days, or until discharge resolves, given high contagiousness in the first week.
• Cold compresses for comfort, applied as needed.
• Stop wearing contact lenses until fully resolved.
• Discard any eye makeup or contact lens solution used during the infection, given the risk of surface contamination and re-inoculation.

Pregnancy/breastfeeding

Cold compresses and lubricants have no systemic exposure concern. Oral acyclovir/valacyclovir for ocular herpetic disease should be discussed with the prescriber managing the pregnancy, but are generally considered reasonably safe when clinically indicated.

Immunocompromised patients

Have a lower threshold to consider herpetic or other atypical causes, and to involve ophthalmology, given a higher risk of severe or vision-threatening disease.

Children

Adenoviral conjunctivitis is common in children and spreads readily in daycare/school settings — reinforce hand hygiene and exclusion from school per local public health guidance until discharge resolves.

If there is no improvement after 3-5 days, or if pain/photophobia develops (suggesting corneal involvement, which can follow adenoviral conjunctivitis in a minority of cases), refer to an ophthalmologist. Chronic unilateral redness should prompt reconsideration of the diagnosis rather than continued observation.

1. Reconfirm the diagnosis — reassess for a red-eye mimic or for herpetic involvement not initially recognized.^[4]
2. Watch specifically for new pain, photophobia, or reduced vision, which can indicate adenoviral keratitis (corneal involvement) developing after the initial conjunctivitis — refer to ophthalmology if this occurs.
3. For a red eye persisting well beyond the expected 1-3 week course, reconsider a bacterial or allergic cause, or refer for specialist assessment.

• Prescribing a topical antibiotic for viral conjunctivitis — does not treat a virus and does not prevent secondary bacterial infection in typical cases.
• Using an ophthalmic corticosteroid or antibiotic/corticosteroid combination without specialist supervision — can worsen undiagnosed herpetic keratitis.
• Missing herpes simplex or herpes zoster ocular involvement by treating every watery red eye as typical adenoviral conjunctivitis.
• Missing a red-eye mimic (angle-closure glaucoma, iritis, scleritis, keratitis) by assuming every red eye is conjunctivitis.
• Overusing ophthalmic vasoconstrictors/decongestants — causes rebound hyperemia and tachyphylaxis; limit to occasional, short-term use (≤3-4 times per month, ≤3 days in a row).
• Underestimating contagiousness — not counselling on hand hygiene and exclusion from school/work during the infectious period.

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Systemic antivirals — herpes simplex/zoster ocular involvement only

Manage jointly with ophthalmology.

Ophthalmic vasoconstrictors/decongestants

Occasional, short-term use only (≤3-4 times/month, ≤3 days in a row) — overuse causes rebound hyperemia and tachyphylaxis.