Conjunctivitis (Pink Eye) — Viral, Bacterial & Allergic Types, Causes & Treatment — Symptoms, Causes & Treatment | MyMedicPlus

Conjunctivitis (pink eye) is inflammation of the conjunctiva — the thin transparent mucous membrane lining the inside of the eyelids and covering the sclera (white of the eye). It is the most common eye condition seen in primary care and emergency departments globally. Conjunctivitis is classified by aetiology: viral (most common — 80% of acute infective conjunctivitis), bacterial (15%), allergic (extremely common — 20–40% of the population is affected at some point), and less commonly toxic/chemical or immune-mediated. Viral and bacterial types are highly contagious and transmitted via direct contact with infected secretions or contaminated hands and surfaces. Allergic conjunctivitis is not infectious. Most cases resolve within 7–14 days with or without treatment, but accurate diagnosis prevents inappropriate antibiotic prescribing (the vast majority of infective cases are viral).

Viral conjunctivitis: adenovirus (serotypes 3, 4, 7, 8, 19, 37) causes 65–90% of viral cases — highly contagious, can cause epidemic keratoconjunctivitis (EKC) outbreaks in workplaces and schools; herpes simplex virus (HSV — dendritic ulcer on fluorescein staining); varicella-zoster virus (with periorbital vesicles); molluscum contagiosum (follicular conjunctivitis with umbilicated lid lesion); enterovirus 70 (epidemic haemorrhagic conjunctivitis). Bacterial conjunctivitis: Staphylococcus aureus and epidermidis (adults); Streptococcus pneumoniae, Haemophilus influenzae (children); Neisseria gonorrhoeae (hyperacute copious purulent discharge — ophthalmological emergency); Chlamydia trachomatis (chronic follicular conjunctivitis in sexually active adults; trachoma in developing world — leading infectious cause of blindness). Allergic conjunctivitis: IgE-mediated reaction to airborne allergens (grass pollen, house dust mite, pet dander — seasonal or perennial); vernal keratoconjunctivitis (severe allergic, typically in young males, atopic eczema/asthma); giant papillary conjunctivitis (from contact lens protein deposits).

Viral conjunctivitis: unilateral initially spreading to both eyes within 24–72 hours, watery or serous discharge, red eye (conjunctival injection), foreign body sensation, follicles (small raised bumps) on the palpebral conjunctiva (tarsal surface), preauricular lymphadenopathy (characteristic of adenoviral conjunctivitis), and photophobia. May be associated with viral upper respiratory tract infection. Bacterial conjunctivitis: purulent or mucopurulent discharge (causes eyelids to stick shut especially on waking — 'glued eyes'), typically bilateral, moderate conjunctival injection. Gonococcal conjunctivitis: copious purulent discharge within 24 hours of onset — urgent ophthalmological referral required (risk of corneal perforation). Allergic conjunctivitis: bilateral intense itching (itching is the cardinal symptom), watery discharge, chemosis (conjunctival oedema), papillae (flat-topped raised lesions on tarsal conjunctiva), and associated allergic rhinitis, atopic eczema. Differentiation: itching strongly suggests allergy; preauricular lymphadenopathy and watery discharge suggest viral; purulent sticky discharge suggests bacterial.

Conjunctivitis is predominantly a clinical diagnosis based on history and examination. Slit-lamp examination by an ophthalmologist or optometrist: assesses the conjunctiva, cornea (fluorescein staining for HSV dendritic ulcer, adenoviral subepithelial infiltrates), anterior chamber (cells — suggesting anterior uveitis rather than conjunctivitis), and intraocular pressure. Conjunctival swabs for culture: indicated for copious purulent discharge (gonorrhoea), treatment failure, newborn conjunctivitis (ophthalmia neonatorum — emergency), and immunocompromised patients. PCR: adenovirus or HSV PCR on conjunctival swab — confirms the diagnosis in epidemic settings. Chlamydial testing (NAAT — nucleic acid amplification test on swab) in chronic follicular conjunctivitis in sexually active adults. Allergy testing (specific IgE, skin prick tests) if seasonal or perennial allergic conjunctivitis does not respond to standard treatment. Differentiate from other red eye causes: uveitis (photophobia, ciliary flush, absent discharge), acute angle-closure glaucoma (severe headache, haloes, fixed mid-dilated pupil — emergency), and episcleritis.

Viral conjunctivitis: no specific antiviral treatment for adenovirus — self-limiting (7–14 days); cool compresses and artificial tears (lubricating drops) for comfort; strict hand hygiene and avoid sharing towels to prevent spread. Topical antihistamines (olopatadine 0.1%, ketotifen) provide symptomatic relief for associated allergic component. HSV conjunctivitis: topical acyclovir 3% eye ointment 5 times daily for 10 days — essential to prevent corneal scarring; systemic antivirals (valacyclovir) for severe or periocular HSV. Bacterial conjunctivitis: self-limiting in most (60% resolved without treatment within 5 days); chloramphenicol 0.5% drops QDS for 5 days or chloramphenicol 1% ointment TDS (first-line in UK — effective and broad-spectrum) reduces duration; fusidic acid 1% drops BD (for Staphylococcal blepharoconjunctivitis). Gonococcal conjunctivitis: IM ceftriaxone 1 g stat + saline eye irrigation; urgent ophthalmological review. Chlamydial conjunctivitis: oral azithromycin 1 g stat or doxycycline 100 mg BD for 7 days; sexual health review and partner notification. Allergic conjunctivitis: allergen avoidance; topical olopatadine 0.2% OD or 0.1% BD (dual antihistamine + mast cell stabiliser), sodium cromoglicate 2% QDS, or nedocromil sodium; topical NSAIDs (ketorolac); short-course topical corticosteroids (prednisolone 0.5%) for severe cases under ophthalmological supervision.

Gonococcal conjunctivitis can cause corneal ulceration and perforation within hours of onset if untreated — it is an ophthalmological emergency requiring same-day systemic IM ceftriaxone. Herpes simplex virus (HSV) keratitis, if not treated promptly with topical acyclovir ointment, causes dendritic ulceration, stromal keratitis, and corneal scarring with permanent visual impairment. Chronic Chlamydia trachomatis conjunctivitis causes trachoma — the leading infectious cause of preventable blindness globally, affecting 1.9 million people; repeated reinfections cause trichiasis (inturned lashes abrading the cornea) and corneal opacity. Ophthalmia neonatorum (neonatal conjunctivitis) from Neisseria gonorrhoeae causes corneal ulceration and permanent blindness within 24-48 hours if untreated with systemic antibiotics — it is an ophthalmic emergency. Bacterial keratitis (corneal infection) in contact lens wearers who continue lens wear during conjunctivitis, particularly from Pseudomonas aeruginosa, causes rapidly progressive corneal ulceration and risk of permanent vision loss.

Viral and bacterial conjunctivitis: meticulous hand hygiene (wash hands frequently with soap and water for 20 seconds — before and after eye contact); avoid touching the eyes; do not share eye drops, makeup, contact lenses, towels, or pillowcases; change pillowcases daily during an infection; discard eye makeup used during infection; contact lens wearers should switch to glasses until conjunctivitis resolves (risk of corneal infection). Children with infective conjunctivitis may attend school once discharge has resolved — no evidence supports mandatory exclusion periods for the standard viral type. Allergic conjunctivitis: allergen avoidance where possible (keep windows closed during high pollen seasons, use air conditioning, wear wraparound sunglasses outdoors); use artificial tears to dilute and wash out allergens; antihistamine eye drops prophylactically before allergen exposure.

Seek emergency ophthalmological review the same day for: copious purulent eye discharge with a very red eye (possible gonococcal conjunctivitis — risk of corneal perforation within hours); vision loss or change; severe eye pain; contact lens wearers with red eye (risk of bacterial keratitis); photophobia (sensitivity to light) suggesting uveitis or keratitis; eye redness in a newborn (ophthalmia neonatorum — any age). Consult your GP or optometrist for: conjunctivitis not improving after 5–7 days of antibiotic drops; recurrent conjunctivitis; symptoms associated with skin blistering around the eye (possible HSV or VZV — needs urgent antiviral treatment); or if you have a corneal contact lens and develop conjunctivitis. Do not delay if vision is affected — delay in treating bacterial keratitis or HSV dendritic ulcer can cause permanent corneal scarring.