Viral Conjunctivitis

Clinical Snapshot

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]

Recognize the Condition

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.

Herpetic ocular involvement (distinct from typical viral conjunctivitis)

Herpes simplex keratoconjunctivitis

Usually unilateral, often with visible vesicles on the eyelid or periorbital skin, and may show a dendritic (branching) corneal lesion on fluorescein staining. This is a corneal, not just conjunctival, process and needs ophthalmology involvement.

Herpes zoster ophthalmicus

Facial vesicles in a V1 (ophthalmic) trigeminal dermatome distribution with ocular involvement; a vesicle on the tip of the nose (Hutchinson's sign) predicts a higher likelihood of ocular involvement and should prompt urgent ophthalmology referral.

Risk Factors

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.

Red Flags & Refer

Refer immediately to an ophthalmologist (or an optometrist if one is not available) for any of the following:

Marked redness concentrated at the corneoscleral junction (limbal/ciliary injection), especially if one-sided.
White corneal opacity or haze.
Moderate-to-severe pain or photophobia not relieved by a test dose of topical anesthetic.
Reduced visual acuity.
An abnormal pupil.
Recent trauma or chemical exposure.
A contact-lens wearer with suspected corneal infiltrate/ulcer.
Chronic unilateral conjunctivitis lasting over 3 weeks.
Suspected herpes simplex ocular involvement (usually unilateral, eyelid vesicles, possible dendritic corneal lesion).
Herpes zoster ophthalmicus (facial V1-dermatome vesicles ± Hutchinson's sign).
Suspected COVID-19-associated conjunctivitis, per current local testing/isolation guidance.^[2]

Assessment & Diagnosis

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 with diffuse conjunctival redness and purulent yellow discharge

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

Viral conjunctivitis with marked diffuse redness and watery discharge

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

Allergic conjunctivitis with conjunctival redness, chemosis, and eyelid swelling

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

Anterior blepharitis with crusting and scale at the base of the eyelashes

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)

Feature	Bacterial conjunctivitis	Viral conjunctivitis	Allergic conjunctivitis	Blepharitis
Laterality	Often one eye first, may spread to the other	Usually starts in one eye, spreads to the other within days	Bilateral, essentially always	Bilateral, essentially always
Discharge	Purulent, thick, yellow-green; lids stuck together on waking	Watery to mucoid; no true pus	Watery, stringy/mucoid	Greasy debris and crusting at the lash base, not a true discharge
Itching	Minimal or absent	Mild, if present	The dominant symptom — if the patient does not report itching, reconsider allergic conjunctivitis	Mild irritation/burning more than itching
Associated findings	May follow otitis media in children; no preauricular node in most cases	Preauricular lymph node, recent URTI, conjunctival membranes, subconjunctival hemorrhage	Chemosis (conjunctival swelling), lid edema, history of atopy/seasonal pattern	Lash crusting, missing/misdirected lashes, recurrent styes, meibomian gland dysfunction
Typical course	Self-limited over 1-2 weeks even without treatment; antibiotics modestly shorten this	Self-limited over 1-3 weeks; highly contagious for the first 3-7 days	Persists as long as allergen exposure continues; recurs seasonally	Chronic, relapsing; managed rather than cured
1st-line management	Often no treatment needed; a topical antibiotic modestly shortens recovery	Supportive care only — cold compresses, lubricants	Remove/avoid the allergen; topical antihistamine/mast-cell stabilizer	Lid hygiene: warm compresses plus lid margin cleansing

Distinguishing bacterial from adenoviral (viral) conjunctivitis by clinical exam alone is genuinely difficult — a point-of-care adenovirus antigen test is available in some settings and can help when the distinction changes management.

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).

Treatment Targets

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

Choose Initial Treatment

Direct treatment rule

1st line, adenoviral conjunctivitis supportive care only — cold compresses and ocular lubricants.

No antiviral or antibiotic is indicated for typical adenoviral conjunctivitis — antibiotics do not treat a virus, and no antiviral has proven benefit for adenoviral conjunctivitis specifically.^[3]

Herpes simplex/zoster ocular involvement requires systemic antiviral treatment (not the adenoviral supportive-care approach) and ophthalmology co-management — this is a fundamentally different disease process from typical viral conjunctivitis, even though it can present with a red, watery eye.

Do not use ophthalmic corticosteroids or antibiotic/corticosteroid combinations — may worsen undiagnosed herpetic keratitis, a serious and largely avoidable error.

Non-Pharmacologic Treatment

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.

Pharmacologic Treatment Options

Drug / intervention	Role	Dose / use	Important adverse effects	Teaching points
Cold compresses Preferred	Symptomatic relief, adenoviral conjunctivitis	Apply as needed, 5-10 minutes	None	First-line and often only treatment needed.
Artificial tears/lubricants Preferred	Symptomatic relief, adenoviral conjunctivitis	As needed	None	Preservative-free formulations preferred with frequent use.
Valacyclovir Special situation	Herpes zoster or herpes simplex ocular involvement	Zoster: 1 g TID PO x 7 days. Simplex: 500 mg TID PO x 7 days	GI upset (uncommon)	Requires ophthalmology co-management for any ocular herpetic involvement.
Acyclovir Special situation	Herpes zoster or herpes simplex ocular involvement	Zoster: 800 mg PO 5 times/day x 7 days. Simplex: 400 mg PO 5 times/day x 7-14 days	GI upset (uncommon)	Alternative to valacyclovir; requires more frequent daily dosing.
Brimonidine ophthalmic Alternative	Short-term redness relief	1 drop Q6-8H PRN, maximum 4 times/day	Pain on instillation	Occasional, short-term use only — overuse causes rebound hyperemia.

Special Populations

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.

Monitoring & Follow-Up

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.

Treatment Failure / Next Step

Reconfirm the diagnosis — reassess for a red-eye mimic or for herpetic involvement not initially recognized.^[4]
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.
For a red eye persisting well beyond the expected 1-3 week course, reconsider a bacterial or allergic cause, or refer for specialist assessment.

Common Errors to Avoid

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.

Clinical Decision Algorithm

Algorithm A — Red-eye triage (apply first, regardless of suspected cause)

Patient presents with a red eye

Assess for warning signs: limbal injection, corneal opacity, pain/photophobia unrelieved by anesthetic, reduced vision, pupil abnormality, trauma, contact-lens-related ulcer, or suspected chlamydial/gonococcal/herpetic/COVID-19 conjunctivitis

Any warning sign present

Refer immediately to ophthalmology (or optometry if unavailable) — do not manage as simple conjunctivitis or blepharitis

No warning signs

Proceed to condition-specific assessment and management

Algorithm B — Viral conjunctivitis management

No red flags; watery discharge, preauricular node, recent URTI

Eyelid vesicles, dendritic corneal lesion, or V1 dermatome facial vesicles

Suspect herpes simplex/zoster ocular involvement — urgent ophthalmology referral + systemic antiviral

Typical watery, bilateral-spreading conjunctivitis, no vesicles

Adenoviral: supportive care only — cold compresses, lubricants, hygiene to limit spread

New pain, photophobia, or reduced vision at any point: refer to ophthalmology for possible keratitis

Drug Tables

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.

No drug treats typical adenoviral conjunctivitis. The systemic antivirals below are for herpes simplex/zoster ocular involvement only — a different disease requiring ophthalmology co-management, not routine viral conjunctivitis.

Systemic antivirals — herpes simplex/zoster ocular involvement only

Manage jointly with ophthalmology.

Drug	Dosage	Adverse effects
Acyclovir	Herpes zoster: 800 mg PO 5 times/day for 7 days Herpes simplex: 400 mg PO 5 times/day for 7-14 days	GI upset (uncommon); well tolerated
Famciclovir	Herpes zoster: 500 mg PO TID for 7 days Herpes simplex: 250 mg PO TID for 7 days	GI upset (uncommon); well tolerated
Valacyclovir	Herpes zoster: 1 g PO TID for 7 days Herpes simplex: 500 mg PO TID for 7 days	GI upset (uncommon); well tolerated

Ophthalmic vasoconstrictors/decongestants

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

Drug	Dosage	Adverse effects	Comments
Naphazoline	All ages: 1-2 drops Q3-4H PRN for 3-4 days	Minor stinging; pupillary dilation and angle-closure glaucoma risk in predisposed patients	For redness/edema in viral conjunctivitis, or minor irritation.
Brimonidine 0.025%	All ages: 1 drop Q6-8H PRN, maximum 4 times/day	Pain on instillation	Does not appear to cause significant rebound hyperemia or tachyphylaxis based on limited evidence.
Phenylephrine ophthalmic	All ages: 1-2 drops QID PRN for up to 3 days	Minor stinging; pupillary dilation and angle-closure glaucoma risk in predisposed patients
Tetrahydrozoline	All ages: 1-2 drops BID-QID	Minor stinging; pupillary dilation and angle-closure glaucoma risk in predisposed patients

References

Conjunctivitis: a systematic review of diagnosis and treatment — JAMA (Azari AA, Barney NP). JAMA 2013;310(16):1721-1729
Bedside diagnosis of the 'red eye': a systematic review — American Journal of Medicine (Narayana S, McGee S). Am J Med 2015;128(11):1220-1224
Adenoviral keratoconjunctivitis — Survey of Ophthalmology (Jhanji V, Chan TC, Li EY, et al.). Surv Ophthalmol 2015;60(5):435-443
Low-dose brimonidine for relief of ocular redness: integrated analysis of four clinical trials — Clinical and Experimental Optometry (Ackerman SL, Torkildsen GL, McLaurin E, et al.). Clin Exp Optom 2019;102(2):131-139
Conjunctivitis Preferred Practice Pattern — American Academy of Ophthalmology (Hoskins Center for Quality Eye Care, PPP Cornea/External Disease Committee). 2023 update, published 2024

Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.