Conjunctivitis — Viral, Bacterial & Allergic Pink Eye Guide — Symptoms, Causes & Treatment | MyMedicPlus

Conjunctivitis is inflammation of the conjunctiva — the thin, transparent membrane covering the white of the eye (sclera) and the inner eyelid surface. It is one of the most common eye conditions, characterised by redness, discharge, and discomfort. The three main types are: viral conjunctivitis (most common, 80% of acute cases — often caused by adenovirus; highly contagious); bacterial conjunctivitis (purulent discharge, common in neonates and children — caused by Staphylococcus, Streptococcus, Haemophilus, Neisseria gonorrhoeae, Chlamydia); and allergic conjunctivitis (triggered by allergens — pollen, dust mite, animal dander — affects 15-20% of the population). Distinguishing between the three main types of conjunctivitis — viral, bacterial, and allergic — is critical for appropriate management, as antibiotic eyedrops are unnecessary and ineffective for viral or allergic conjunctivitis and contribute directly to antimicrobial resistance when overprescribed in primary care.

Viral conjunctivitis: adenovirus (types 3, 7, 8, 19 — epidemic keratoconjunctivitis, EKC — highly contagious); herpes simplex virus (serious — requires antiviral treatment); enterovirus and coxsackievirus (haemorrhagic conjunctivitis); COVID-19 (ocular manifestation in 1-3% of cases). Bacterial conjunctivitis: most common bacteria — Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae (children); Neisseria gonorrhoeae (neonatal, or in sexually active adults — hyperacute, severe); Chlamydia trachomatis (neonatal conjunctivitis; chronic/adult inclusion conjunctivitis — STI). Allergic conjunctivitis: seasonal (SAC — pollen); perennial (PAC — dust mite, pet dander); vernal keratoconjunctivitis (VKC — severe, affects young males); giant papillary conjunctivitis (contact lens irritation). Chemical or irritant conjunctivitis (from chlorine in swimming pools, air pollutants, or preservatives in contact lens solutions) and neonatal conjunctivitis (ophthalmia neonatorum — from Neisseria gonorrhoeae or Chlamydia trachomatis acquired during birth) are important additional categories each requiring specific targeted management approaches.

Viral conjunctivitis: watery discharge, redness (conjunctival injection), photophobia, foreign body sensation, often with preceding upper respiratory infection, and pre-auricular lymph node enlargement (tender swollen gland in front of the ear). Both eyes often affected (unilateral initially, rapidly bilateral). Bacterial conjunctivitis: mucopurulent (thick yellow-green) discharge causing eyelids to stick together (especially on waking), redness, and mild discomfort. Typically unilateral or starting in one eye. Neisseria gonorrhoeae conjunctivitis: copious purulent discharge, eyelid swelling, corneal ulceration — medical emergency. Allergic conjunctivitis: intense bilateral itching (the cardinal symptom), watery discharge, chemosis (conjunctival swelling), seasonal occurrence, associated allergic rhinitis or atopic history. VKC: severe photophobia, ropy discharge, giant papillae ('cobblestones') under the upper eyelid.

Diagnosis is primarily clinical, based on history and eye examination. Features differentiating type: watery discharge + pre-auricular node → viral; purulent discharge + no itching → bacterial; intense itching + no discharge (or watery) + seasonal pattern + atopy → allergic. Slit-lamp examination reveals: follicles in viral conjunctivitis; papillae in bacterial/allergic; corneal involvement in herpes simplex (dendritic ulcer with fluorescein staining) or adenoviral EKC (corneal subepithelial infiltrates). Conjunctival swabs for bacterial culture (Neisseria, Chlamydia suspected); PCR testing for viral pathogens. RADT (rapid adenovirus detection test) available in some settings. Important to rule out serious conditions: keratitis, uveitis, acute angle-closure glaucoma — these cause visual loss, photophobia, ciliary injection, and pain and require urgent ophthalmology referral.

Viral conjunctivitis: self-limiting — resolves in 7-14 days without specific treatment. Supportive care: artificial tears (lubricating eyedrops, e.g., hypromellose), cool compresses, remove contact lenses until resolved. Avoid touching eyes and practice strict hand hygiene to prevent spread. Herpes simplex conjunctivitis: topical aciclovir eye ointment 5x/day or oral valaciclovir — urgent ophthalmology referral. Bacterial conjunctivitis: most acute bacterial conjunctivitis is self-limiting (resolves in 7-10 days without antibiotics). However, antibiotic eyedrops (chloramphenicol 0.5% every 2 hours then reducing, or fusidic acid gel twice daily) shorten the duration and reduce contagion. Neisseria gonorrhoeae: systemic antibiotics (ceftriaxone IV/IM) plus copious ocular irrigation — medical emergency. Chlamydia: oral azithromycin or doxycycline plus topical tetracycline. Allergic conjunctivitis: topical antihistamines/mast cell stabilisers (olopatadine, azelastine, ketotifen — once or twice daily); cool compresses; avoid allergen. Severe VKC/atopic keratoconjunctivitis: topical ciclosporin or tacrolimus; systemic antihistamines; referral to ophthalmologist.

Viral conjunctivitis from adenovirus can cause subepithelial corneal infiltrates in EKC — causing photophobia and reduced vision for weeks to months. Herpes simplex keratitis (dendritic ulcer) causing permanent corneal scarring and vision loss if untreated. Gonococcal conjunctivitis (Neisseria gonorrhoeae) rapidly causes corneal perforation within hours if untreated — a sight-threatening emergency. Neonatal conjunctivitis (ophthalmia neonatorum) from Neisseria or Chlamydia can cause blindness if not treated urgently. Chlamydial trachoma — chronic conjunctivitis from Chlamydia trachomatis serovars A-C — is the leading infectious cause of blindness globally, affecting 2 million people in endemic regions. Allergic keratoconjunctivitis (VKC/AKC) causes corneal scarring from chronic rubbing and pannus formation if not adequately managed.

Viral conjunctivitis is highly contagious — wash hands frequently and thoroughly; avoid touching eyes; use separate face cloths and towels; avoid sharing eye cosmetics or contact lenses. Discard soft contact lenses worn during viral conjunctivitis and sterilise rigid lenses. Do not attend school or work during the acute contagious phase of viral EKC (adenoviral conjunctivitis — highly infectious for up to 2 weeks). Allergic conjunctivitis prevention: reduce allergen exposure (air purifiers, allergen-proof bedding); wear sunglasses outdoors during pollen season; stay indoors on high-pollen days. Begin antihistamine eyedrops 2 weeks before the pollen season (preemptive therapy). Sublingual or subcutaneous allergen immunotherapy reduces long-term allergic conjunctivitis sensitivity. STI screening and treatment prevents gonococcal and chlamydial conjunctivitis.

Seek same-day or emergency ophthalmology assessment for: any visual loss or blurring (beyond surface discharge) — conjunctivitis does not impair vision; severe eye pain (conjunctivitis causes discomfort, not severe pain — intense pain may indicate keratitis, uveitis, or acute glaucoma); significant photophobia (severe light sensitivity); corneal cloudiness or white spot visible on the cornea; copious profuse purulent discharge within 24 hours of onset in a newborn (ophthalmia neonatorum — urgent systemic antibiotic treatment required to prevent blindness); very profuse purulent discharge in a sexually active adult (possible gonococcal conjunctivitis — corneal perforation risk without treatment); and red eye in a contact lens wearer (remove lenses immediately — risk of Pseudomonas keratitis). Also seek urgent care for: a red painful eye with headache, nausea, vomiting, and a fixed semi-dilated pupil — this is acute angle-closure glaucoma, a medical emergency requiring immediate treatment to save vision.