Bacterial Conjunctivitis

Evidence-based assessment and management of bacterial conjunctival infection. Comprehensive guide covering etiology, pathogenesis, classification, diagnosis, and treatment protocols for optometry practice.

Last updated: March 2026

Bacterial conjunctivitis: diffuse conjunctival injection, mucopurulent discharge at medial canthus, and papillary tarsal reaction

Bacterial conjunctivitis is an acute or chronic infection of the conjunctival epithelium caused by pathogenic bacteria. It is one of the most common causes of red eye presenting in primary eye and general medical care, characterised by conjunctival hyperaemia, mucopurulent or purulent discharge, and eyelid matting — particularly on waking. Although the majority of non-gonococcal cases are self-limiting, accurate diagnosis is essential to distinguish bacterial from viral and allergic aetiologies, to identify sight-threatening forms (gonococcal, chlamydial, neonatal), and to guide appropriate antimicrobial therapy. The condition occurs across all age groups with distinct microbiological profiles in neonates, children, and adults.

Common Causative Organisms

Staphylococcus aureus — most common adult pathogen; associated with blepharitis and chronic lid disease
Staphylococcus epidermidis — coagulase-negative; common commensal, can cause opportunistic infection
Streptococcus pneumoniae — common in children; produces copious mucopurulent discharge and subconjunctival haemorrhage
Haemophilus influenzae — predominant in paediatric populations; associated with concurrent otitis media
Moraxella catarrhalis — gram-negative diplococcus; common in children, often co-exists with respiratory infection
Pseudomonas aeruginosa — uncommon in community settings; important in contact lens wearers and nosocomial infections; can rapidly progress to keratitis
Neisseria gonorrhoeae — sexually transmitted; causes hyperacute conjunctivitis with copious purulent discharge; risk of corneal perforation within 24–48 hours
Chlamydia trachomatis (serovars D–K) — oculogenital inclusion conjunctivitis; most common bacterial STI-associated conjunctivitis in adults; requires systemic therapy

Neonatal Pathogens (Ophthalmia Neonatorum)

Neisseria gonorrhoeae — presents within 2–5 days of birth; profuse purulent discharge; emergency ophthalmic referral
Chlamydia trachomatis — most common infectious cause in developed countries; presents at 5–14 days; risk of pneumonitis if untreated
Chemical (silver nitrate prophylaxis) — sterile chemical conjunctivitis within 24 hours; self-resolving
Other organisms: Staphylococcus, Streptococcus, E. coli, Herpes simplex virus (neonatal HSV requires urgent antiviral therapy)

Less Common / Special Contexts

Methicillin-resistant Staphylococcus aureus (MRSA) — increasing prevalence; important in healthcare workers and nosocomial setting
Listeria monocytogenes — rare; associated with granulomatous conjunctivitis (Parinaud’s oculoglandular syndrome)
Corynebacterium diphtheriae — rare; membranous conjunctivitis; notifiable disease

Mechanism of Infection

Colonisation and adhesion: Bacteria breach conjunctival defence mechanisms (lysozyme, lactoferrin, secretory IgA, antimicrobial peptides) and adhere to the conjunctival epithelium via surface adhesins and pili
Invasion and toxin production: Organisms elaborate proteases, lipases, and cytotoxins that disrupt the epithelial tight junctions and mucosal barrier; S. aureus produces exotoxins (TSST-1, protein A) that activate T-cells and mast cells; gonococcal IgA protease cleaves secretory IgA
Innate immune activation: Pattern recognition receptors (Toll-like receptors) on conjunctival epithelial cells detect bacterial pathogen-associated molecular patterns (PAMPs), triggering NF-κB–mediated cytokine and chemokine release (IL-1β, IL-6, IL-8, TNF-α)
Neutrophil recruitment: IL-8 and complement fragments (C3a, C5a) drive massive neutrophil influx into the conjunctival stroma and tear film — forming the characteristic purulent exudate
Vascular response: Inflammatory mediators produce vasodilation and increased vascular permeability of conjunctival vessels, resulting in the clinical sign of diffuse conjunctival injection
Papillary reaction: Continued antigenic stimulation produces epithelial hyperplasia and inflammatory cell infiltration of the substantia propria, elevating the conjunctival epithelium into papillae visible on the palpebral conjunctiva
Goblet cell disruption: Bacterial proteases and inflammatory cytokines reduce mucin production, destabilising the tear film and compounding surface damage

Gonococcal Pathogenesis (Hyperacute)

Neisseria gonorrhoeae possesses unique virulence factors — type IV pili, outer membrane proteins (Opa, Por), and IgA protease — that enable penetration of intact conjunctival epithelium and rapid corneal invasion. This direct invasion capacity (unlike most other bacterial pathogens) explains the ability to penetrate an intact corneal epithelium and produce perforation within 24–48 hours without treatment, mandating emergency management.

By Clinical Onset and Severity

Hyperacute bacterial conjunctivitis: Onset within hours; copious purulent discharge; most commonly gonococcal; sight-threatening emergency
Acute bacterial conjunctivitis: Onset over 1–3 days; mucopurulent discharge; most common form; typically caused by S. aureus, H. influenzae, S. pneumoniae
Subacute / chronic bacterial conjunctivitis: Prolonged course (>4 weeks); often associated with Chlamydia trachomatis (inclusion conjunctivitis), Moraxella, or Staphylococcus

By Age Group

Neonatal (Ophthalmia neonatorum, 0–28 days): Acquired intrapartum from maternal genital secretions; most commonly chlamydial or gonococcal; notifiable condition
Paediatric (1 month–18 years): H. influenzae and S. pneumoniae predominate; commonly bilateral with concurrent upper respiratory tract infection; associated with otitis media in H. influenzae infections (Brazilian purpuric fever variant)
Adult: S. aureus and S. epidermidis predominate; STI-related organisms (gonococcal, chlamydial) must be considered in sexually active adults with chronic or atypical features
Immunocompromised: Broader organism spectrum including Pseudomonas, Serratia, atypical mycobacteria; higher risk of corneal involvement

By Conjunctival Reaction Pattern

Pattern	Morphology	Common Causes
Papillary	Flat polygonal elevations with central vascular core; <1 mm	Bacterial, toxic, mechanical
Follicular	Pale, avascular, dome-shaped elevations; 0.5–2 mm	Chlamydial, viral (note: follicular suggests chlamydial or viral, not typical pyogenic bacteria)
Membranous	True membrane (bleeds on removal); pseudomembrane (peels cleanly)	Gonococcal, S. pyogenes, C. diphtheriae
Papillary + petechial haemorrhage	Fine subconjunctival haemorrhages with papillae	S. pneumoniae, H. influenzae (especially children)

Age extremes: Neonates (exposure to maternal genital flora intrapartum) and elderly (impaired mucosal immunity, reduced tear volume, eyelid laxity)
Contact lens wear: Disrupts corneal epithelium, reduces tear film exchange, creates reservoir for gram-negative organisms especially Pseudomonas aeruginosa
Chronic blepharitis: Abnormal lid flora (S. aureus overgrowth) directly contaminates the conjunctival surface
Dry eye disease: Reduced lysozyme, lactoferrin, and secretory IgA concentrations weaken antimicrobial tear film defence
Nasolacrimal duct obstruction: Stagnant tear pooling in the lacrimal sac provides a reservoir for bacterial proliferation and recurrent conjunctivitis
Sexually transmitted infections: Active gonorrhoea or chlamydia infection in the patient or their partners; auto-inoculation from genital secretions
Immunocompromised states: HIV, systemic corticosteroid use, chemotherapy, diabetes mellitus — reduced local and systemic antimicrobial defences
Healthcare / institutional exposure: Nosocomial spread in hospitals, daycare centres, and schools; hand-to-eye transmission
Trauma or ocular surgery: Disruption of conjunctival epithelial barrier facilitates bacterial entry
Topical corticosteroid use: Impairs local immune surveillance, may unmask or worsen latent bacterial infection
Poor hand hygiene: Principal route of transmission in community settings

External / Adnexal Signs

Eyelid oedema: Mild to moderate lid swelling, especially in H. influenzae and gonococcal infections
Eyelid matting / crusting: Mucopurulent exudate causing lashes to stick together, typically worse on waking — a key differentiator from viral conjunctivitis
Preauricular lymphadenopathy: Typically absent in bacterial conjunctivitis (distinguishes from viral EKC where it is characteristically present)

Conjunctival Signs

Diffuse conjunctival injection: Uniform bulbar and tarsal conjunctival hyperaemia; involvement of the fornices differentiates from episcleritis/scleritis
Mucopurulent or purulent discharge: Mucopurulent in non-gonococcal disease; profuse purulent (copious pus) in gonococcal infection
Papillary reaction: Flat, polygonal elevations on palpebral (tarsal) conjunctiva with central vascular core; typical of bacterial and toxic aetiology
Chemosis: Conjunctival oedema with boggy, gelatinous appearance; more pronounced in gonococcal and severe infections
Subconjunctival petechiae: Characteristic of S. pneumoniae and H. influenzae infections in children
Membrane / pseudomembrane formation: Rare in typical bacterial conjunctivitis; when present, raises concern for gonococcal, streptococcal, or diphtheria infection
Follicular reaction: Absent or minimal in pyogenic bacterial infection; prominent follicles suggest chlamydial or viral aetiology

Corneal Signs

Punctate epithelial erosions (PEE): Inferior or diffuse fluorescein-staining punctate erosions in moderate-to-severe cases
Peripheral infiltrates: Staphylococcal marginal keratitis — sterile, crescent-shaped limbal infiltrates at 2, 4, 8, and 10 o’clock with a clear zone from the limbus; immune-mediated (not infectious)
Central infiltrate / ulcer: Rare in typical bacterial conjunctivitis; development of an infiltrate or ulcer mandates urgent referral to exclude bacterial keratitis
Gonococcal corneal involvement: Rapid central ulceration and potential perforation — hallmark of untreated hyperacute gonococcal conjunctivitis

Laterality Pattern

Typically begins unilaterally and spreads to the fellow eye via hand-to-eye transmission within 1–2 days
Gonococcal and chlamydial conjunctivitis may present bilaterally from the outset
Bilateral simultaneous onset in an adult without prior unilateral involvement suggests viral or allergic aetiology

Cardinal Symptoms

Discharge: Mucopurulent or purulent — patients describe a thick, sticky, yellow-green discharge; eyelids "glued shut" on waking is a classic complaint highly specific for bacterial aetiology
Redness: Diffuse ocular redness, often beginning in one eye; patients commonly report that their eye "looks very red" or is "bloodshot"
Foreign body sensation / grittiness: Mild to moderate; less severe than in dry eye or trichiasis; more scratchy than burning
Mild ocular discomfort: Burning, irritation; unlike the deep boring pain of scleritis or the photophobic pain of iritis
Eyelid swelling: Sensation of heaviness or puffiness of the eyelids, particularly in H. influenzae infections in children

Symptoms Typically Absent (Important Negatives)

Significant itch: Itch is the hallmark of allergic conjunctivitis; its presence should prompt reconsideration of the diagnosis
Photophobia: Its presence suggests corneal involvement (keratitis), anterior uveitis, or corneal ulceration — requires urgent assessment
Significant visual loss: Vision should not be substantially reduced; if VA is reduced and does not improve with blinking (clearing discharge), investigate urgently for corneal involvement
Severe deep pain: Raises concern for scleritis, endophthalmitis, or angle-closure glaucoma — not consistent with uncomplicated conjunctivitis

Associated Systemic Symptoms

Upper respiratory tract infection symptoms (sore throat, rhinorrhoea) — commonly co-present with H. influenzae conjunctivitis in children
Ear pain or discharge — otitis media in paediatric H. influenzae conjunctivitis ("conjunctivitis-otitis syndrome")
Urethral or vaginal discharge — suggestive of gonococcal or chlamydial STI; requires sexual health history

Ocular Complications

Bacterial keratitis: Corneal extension of infection leading to stromal infiltration, ulceration, and potential perforation — highest risk with Pseudomonas in contact lens wearers and Neisseria gonorrhoeae
Corneal scarring: Following resolution of keratitis; may cause permanent visual impairment
Staphylococcal marginal keratitis: Immune-mediated peripheral corneal infiltrates; can be mistaken for infectious keratitis; recurrent if underlying blepharitis is not addressed
Corneal perforation: Specific to untreated gonococcal conjunctivitis; can occur within 24–48 hours of symptom onset
Preseptal (periorbital) cellulitis: Spread of infection to the eyelid tissues anterior to the orbital septum; more common in children; requires systemic antibiotics
Orbital cellulitis: Rare; spread posterior to the orbital septum; sight-threatening emergency requiring intravenous antibiotics and urgent specialist care
Conjunctival scarring (symblepharon): Rare in typical bacterial conjunctivitis; may occur with membranous forms (diphtheria, severe gonococcal)
Antibiotic-induced toxicity: Prolonged topical antibiotic use causes ocular surface toxicity, epithelial erosion, and secondary dry eye

Systemic Complications

Pneumonitis (Chlamydia trachomatis in neonates): 10–20% of neonates with chlamydial conjunctivitis develop chlamydial pneumonia if untreated — systemic erythromycin required
Disseminated gonococcal infection (DGI): Haematogenous spread of N. gonorrhoeae causing septic arthritis, skin lesions (petechiae, pustules), tenosynovitis; rare but serious
Bacteraemia / sepsis: Rare; more likely in immunocompromised patients or neonates

Associated Systemic Conditions

Sexually transmitted infections (gonorrhoea / chlamydia): Conjunctivitis may be the presenting feature of an undiagnosed genital STI; referral to sexual health services and partner notification are essential components of management
Concurrent otitis media (H. influenzae): The conjunctivitis-otitis syndrome in children — concurrent acute otitis media in 25–50% of H. influenzae conjunctivitis; systemic amoxicillin-clavulanate is indicated rather than topical antibiotics alone
Upper respiratory tract infection: Concurrent sinusitis or rhinitis can spread organisms to the conjunctiva via the nasolacrimal duct or direct contact
Rosacea: Chronic ocular rosacea with meibomian gland dysfunction predisposes to recurrent staphylococcal conjunctivitis; long-term lid hygiene and oral doxycycline therapy targets the underlying condition
Reactive arthritis (formerly Reiter syndrome): The classic triad of conjunctivitis (or uveitis), urethritis, and arthritis following enteric or STI infection (Chlamydia, Salmonella, Shigella, Campylobacter); HLA-B27 associated
Parinaud’s oculoglandular syndrome: Unilateral granulomatous conjunctivitis with ipsilateral preauricular or submandibular lymphadenopathy from Bartonella henselae (cat-scratch disease), Francisella tularensis, or other organisms; systemic workup required
Diabetes mellitus: Elevated glucose in tear film promotes bacterial proliferation; impaired neutrophil function; higher risk of severe or recurrent bacterial conjunctivitis
HIV / AIDS: Immunocompromised patients are susceptible to unusual bacterial pathogens and may have more severe or atypical presentations

When to Investigate for Systemic Disease

Recurrent or chronic bacterial conjunctivitis — consider nasolacrimal duct obstruction, dry eye, immunodeficiency, or occult STI
Conjunctivitis in a sexually active adult that does not resolve with topical antibiotics — chlamydial or gonococcal aetiology
Conjunctivitis with arthritis and urethritis — reactive arthritis; rheumatology and sexual health referral
Unilateral granulomatous conjunctivitis with lymphadenopathy — Parinaud’s syndrome; infectious disease or internal medicine workup

Clinical History

Duration of symptoms and speed of onset (hyperacute <24 h → gonococcal; acute 1–3 days → typical bacterial; chronic >4 weeks → chlamydial)
Character of discharge: mucopurulent vs. watery (viral) vs. mucoid-stringy (allergic)
Unilateral or bilateral onset; fellow eye involvement over time
Associated systemic symptoms: URTI, ear pain, sore throat, joint pain, urethral discharge
Sexual history: new partners, STI history, unprotected intercourse
Contact lens wear type, overnight wear, lens hygiene practices
Prior episodes; response to previous topical antibiotics
Immunosuppression, systemic medication, atopic history
Exposure history: sick contacts (especially in schools or households), travel to trachoma-endemic regions

Clinical Examination

1. Visual Acuity:

Assess unaided and pinhole VA; blurring from discharge should improve after blinking
Persistent VA reduction after blinking implies corneal involvement — urgent assessment required

2. External Examination:

Assess eyelid oedema, discharge character and volume, eyelash crusting
Palpate preauricular lymph node — enlargement suggests viral aetiology
Inspect skin for rosacea stigmata, periocular dermatitis, vesicles (HSV/HZV)

3. Slit Lamp Biomicroscopy:

Conjunctiva (bulbar): Document distribution and degree of injection; note chemosis; identify subconjunctival haemorrhage
Palpebral conjunctiva (evert upper and lower lids): Grade papillary reaction (fine <0.3 mm, medium 0.3–1 mm, large/giant >1 mm); follicles; membrane or pseudomembrane
Cornea: Fluorescein staining with cobalt blue filter for PEE, abrasions, infiltrates, ulcers; Rose Bengal or lissamine green for mucus filaments (chlamydial)
Anterior chamber: Grade cells and flare; presence of AC reaction raises concern for uveitis — not expected in isolated conjunctivitis
Lid margin: Posterior blepharitis, meibomian plugging (suggests staphylococcal aetiology)

4. Intraocular Pressure:

Assess IOP when the diagnosis is uncertain, when there is significant photophobia, or when vision is reduced, to exclude acute angle-closure glaucoma in the differential

Microbiological Investigations

Routine swab culture is not required for typical acute bacterial conjunctivitis. Investigations are indicated in the following circumstances:

Conjunctival swab for M/C/S (microscopy, culture and sensitivity): Hyperacute conjunctivitis; neonates; suspected MRSA; failed topical antibiotic therapy; contact lens wearers with corneal involvement; immunocompromised patients
Chlamydia and gonorrhoea NAAT (nucleic acid amplification test): Any adult with chronic follicular conjunctivitis, sexually active young adults, or suspected STI-related aetiology; conjunctival swab sent in chlamydia/GC transport medium
Conjunctival scraping for Giemsa staining: Intracytoplasmic inclusion bodies (Halberstaedter-Prowazek bodies) are pathognomonic for chlamydial conjunctivitis; less sensitive than NAAT
Gram stain of discharge: Gram-negative intracellular diplococci — diagnostic of gonococcal conjunctivitis; enables rapid presumptive diagnosis while culture is pending
Blood cultures: If systemic sepsis is suspected (neonates, severely immunocompromised, signs of DGI)

Clinical Decision Aid — Bacterial vs. Viral Conjunctivitis

Feature	Bacterial	Viral (Adenoviral)	Allergic
Discharge	Mucopurulent / purulent	Watery	Mucoid / stringy
Morning lid matting	Prominent ✓	Mild	Absent
Itch	Absent	Absent / mild	Prominent ✓
Preauricular LN	Usually absent	Often present ✓	Absent
Conjunctival reaction	Papillary	Follicular	Papillary ± chemosis
Laterality onset	Unilateral → bilateral	Unilateral → bilateral	Bilateral simultaneous
Systemic features	URTI (H. flu), STI	URTI, fever, pharyngitis	Hayfever, atopy

Singapore Optometry Scope Note: Optometrists in Singapore are not permitted to prescribe or initiate antibiotic therapy. All cases requiring topical or systemic antibiotics must be referred to a medical doctor or ophthalmologist. Corneal assessment using fluorescein and slit lamp biomicroscopy is within scope. Non-contact fundus assessment may be performed using slit lamp biomicroscopy with a condensing lens (e.g. 90D) — dilation is not performed by optometrists in Singapore, and diagnostic equipment approved for optometric fundus assessment should be used where indicated. Gonococcal or chlamydial conjunctivitis, neonatal conjunctivitis, or any case with corneal infiltrates or reduced VA must be referred to an ophthalmologist or emergency department promptly.

General Measures (All Cases)

Lid hygiene and ocular irrigation: Regular saline irrigation or warm compress/cotton wool cleaning to remove discharge; reduces bacterial load and improves patient comfort
Infection control counselling: Handwashing, avoid touching eyes, separate towels and pillowcases, avoid sharing eye drops; do not share eye makeup; exclude from school / childcare until discharge resolves (institutional policy varies)
Contact lens cessation: Discontinue contact lens wear for the duration of infection and 48 hours after resolution; discard worn lenses and lens case; resume only after symptom-free interval
Lubricating drops: Preservative-free artificial tears as adjunct to reduce surface discomfort and dilute bacterial toxins

Topical Antibiotic Therapy

Topical antibiotics shorten disease duration and reduce infectivity. They are most beneficial in moderate-to-severe disease, immunocompromised patients, contact lens wearers, and when rapid return to activities is required. Mild uncomplicated cases may be managed expectantly with hygiene measures alone.

First-line (Non-gonococcal Acute Bacterial Conjunctivitis):

Chloramphenicol 0.5% eye drops: 1 drop 2-hourly (first 48 h), then QID for 5–7 days; broad-spectrum, cost-effective; first-line in many guidelines (UK, Australia); caution: rare aplastic anaemia risk with systemic absorption; avoid in neonates and pregnancy
Fusidic acid 1% viscous drops (Fucithalmic): 1 drop BD for 7 days; effective against gram-positives (S. aureus, S. epidermidis); patient-friendly BD dosing; good choice in blepharitis-associated staphylococcal conjunctivitis
Tobramycin 0.3% drops: 1–2 drops QID for 7 days; broad-spectrum; good gram-negative coverage including Pseudomonas; preferred in contact lens wearers or when gram-negative organisms suspected
Ciprofloxacin 0.3% drops: 1–2 drops QID for 7 days; fluoroquinolone; broad-spectrum; reserve for severe cases or contact lens-associated infections to preserve fluoroquinolone efficacy

Paediatric Considerations:

H. influenzae conjunctivitis with concurrent otitis media: systemic amoxicillin-clavulanate is indicated (topical antibiotics alone are insufficient for the otitis media component)
Chloramphenicol is generally avoided in neonates; tobramycin or erythromycin ophthalmic ointment are preferred in young infants

Management of Specific High-Risk Forms

Gonococcal Conjunctivitis (Emergency — Refer Immediately)

Urgent same-day ophthalmology / emergency department referral — risk of corneal perforation within 24–48 hours
Systemic ceftriaxone 1 g IM single dose (adults) — first-line; covers PPNG (penicillinase-producing N. gonorrhoeae)
Topical ciprofloxacin or gentamicin drops hourly as adjunct while awaiting specialist review
Ocular irrigation with saline to mechanically remove purulent exudate
Partner treatment and sexual health referral mandatory; screen for co-infection with Chlamydia

Adult Chlamydial Conjunctivitis (Refer for Systemic Therapy)

Topical antibiotics alone are insufficient — systemic therapy required
Azithromycin 1 g oral single dose (first-line, Chlamydia trachomatis serovars D–K)
Doxycycline 100 mg BD for 7 days — alternative; avoid in pregnancy
Sexual health referral for partner management and STI screening

Ophthalmia Neonatorum (Urgent Referral)

Any conjunctivitis in a neonate (<28 days) requires urgent ophthalmology and paediatric assessment
Gonococcal: systemic ceftriaxone 25–50 mg/kg IV/IM; topical irrigation
Chlamydial: oral erythromycin ethylsuccinate 50 mg/kg/day in 4 divided doses for 14 days (prevents pneumonitis)
Maternal screening and treatment for both partners is mandatory

Staphylococcal Marginal Keratitis (Immune-mediated)

Combined topical antibiotic–steroid (e.g. chloramphenicol 0.5% + dexamethasone 0.1%) — addresses immune response and secondary infection
Treat underlying posterior blepharitis: lid scrubs, warm compresses, topical azithromycin; consider oral doxycycline for MGD
Monitor for steroid-induced IOP rise; refer to ophthalmology for steroid initiation and monitoring

Treatment Summary by Severity

Severity	Clinical Features	Management
Mild	Mild injection, minimal discharge, VA normal	Lid hygiene, saline irrigation, lubricants; consider topical antibiotics (chloramphenicol or fusidic acid); review in 7 days
Moderate	Significant injection, mucopurulent discharge, lid matting, mild PEE	Topical antibiotics (chloramphenicol 2-hrly → QID); lid hygiene; lubricants; review in 5–7 days; swab if contact lens wearer
Severe	Profuse discharge, significant eyelid oedema, corneal PEE or marginal infiltrates	Intensive topical antibiotics; conjunctival swab; refer to ophthalmology if no improvement in 48 hours or corneal involvement
Hyperacute / High-risk	Profuse purulent discharge <24 h, neonates, STI context, corneal infiltrate, VA loss	Immediate referral to ophthalmology / emergency department; conjunctival swab and Gram stain; systemic antibiotics

Refer to Ophthalmology / Emergency Department for:

Immediate / same-day referral:

Suspected gonococcal conjunctivitis (hyperacute onset, copious pus)
Neonatal conjunctivitis (any aetiology in infant <28 days)
Corneal infiltrate, ulcer, or perforation
Reduced VA not clearing with blink
Significant photophobia (raises concern for keratitis or uveitis)
Preseptal or orbital cellulitis

Routine referral:

No improvement after 5–7 days of appropriate topical antibiotics
Suspected chlamydial or other STI-associated conjunctivitis (requires systemic therapy)
Recurrent bacterial conjunctivitis (investigate nasolacrimal obstruction, immunodeficiency)
MRSA-suspected infection or unusual organism on culture

General Prognosis

Uncomplicated acute bacterial conjunctivitis: Excellent prognosis; the majority of non-gonococcal, non-chlamydial cases are self-limiting within 7–14 days without antibiotics; topical treatment accelerates resolution by 2–3 days
With topical antibiotic therapy: Clinical cure rates of 70–80% at day 5 with chloramphenicol vs. 55–60% placebo in clinical trials (Rose et al., NEJM 2005); discharge resolves within 2–5 days
No permanent visual sequelae in the absence of corneal involvement in typical acute disease
Recurrence: Common if predisposing factors (blepharitis, dry eye, nasolacrimal obstruction, contact lens misuse) are not addressed; underlying cause must be identified and managed

Prognosis by Aetiology

Aetiology	Expected Outcome	Key Determinant
S. aureus, H. influenzae, S. pneumoniae	Excellent; self-limiting 7–14 days	Address underlying blepharitis
Chlamydial (adult)	Good with systemic therapy; chronic if untreated	Systemic azithromycin; partner treatment
Pseudomonas (contact lens)	Good if treated early; poor if keratitis develops	Early intensive fluoroquinolone therapy
Gonococcal	Sight-threatening without immediate treatment; good with prompt systemic antibiotics	Hours matter — immediate referral
Neonatal (any)	Good with prompt treatment; vision loss / pneumonitis if delayed	Speed of diagnosis and systemic therapy

Antimicrobial Resistance

Increasing resistance to topical antibiotics is an emerging concern in community-acquired bacterial conjunctivitis. Staphylococcal resistance to chloramphenicol and quinolones has been documented in multiple regions. Topical antibiotic stewardship — reserving fluoroquinolones for severe or contact lens-related infections — is recommended. Culture and sensitivity testing guides therapy when first-line agents fail.

Condition	Key Differentiating Features	Red Flags / Action
Viral Conjunctivitis (Adenoviral / EKC)	Watery discharge; prominent follicles; preauricular lymphadenopathy; URTI history; highly contagious; no response to topical antibiotics	EKC subepithelial infiltrates → refer if VA affected
Allergic Conjunctivitis	Bilateral; intense itch; chemosis; mucoid stringy discharge; seasonal or perennial; personal/family atopic history; no papillary response to antibiotics	VKC shield ulcer → urgent referral
Dry Eye Disease	Chronic bilateral burning/grittiness; reduced TBUT and Schirmer; SPK in interpalpebral zone; no significant discharge; symptoms worse at end of day	Persistent epithelial erosion → refer
Episcleritis	Sectoral redness without discharge; mild discomfort; blanches with phenylephrine; no papillary or follicular reaction	Rule out scleritis (deep pain, no blanching)
Anterior Uveitis (Iritis)	Ciliary (perilimbal) flush; photophobia; pain; reduced VA; keratic precipitates; AC cells and flare; no discharge	Urgent ophthalmology referral — sight-threatening
Acute Angle-Closure Glaucoma	Severe pain; nausea/vomiting; halos; mid-dilated fixed pupil; corneal oedema; markedly elevated IOP; no discharge	Ocular emergency — immediate referral
Bacterial Keratitis	Significant pain; photophobia; reduced VA; corneal infiltrate or ulcer on slit lamp; fluorescein staining defect; discharge may be present	Urgent ophthalmology referral — sight-threatening
Chlamydial Conjunctivitis	Chronic (>4 weeks); prominent follicles (inferior fornix); mucopurulent discharge; fails topical antibiotics; STI history; superior pannus in trachoma	NAAT testing; systemic antibiotics; sexual health referral
Toxic / Medicamentous Conjunctivitis	Chronic inferior papillary/follicular reaction; history of topical medication use (antiglaucoma, preservative-containing drops); inferior corneal SPK; improves on cessation	Identify and withdraw offending agent
Nasolacrimal Duct Obstruction	Epiphora; discharge expressed from punctum on lacrimal sac massage; chronic or recurrent mucopurulent discharge; no significant injection in the absence of dacryocystitis	Dacryocystitis requires urgent referral

“Glued eyelids on waking” is the most clinically useful discriminator for bacterial vs. viral conjunctivitis; its presence has a positive predictive value of approximately 73–89% for bacterial aetiology in some clinical decision studies
Always evert the upper eyelid to examine the tarsal conjunctiva — papillary reaction, follicles, membrane formation, and foreign bodies can only be confidently assessed on eversion
Absent preauricular lymphadenopathy strongly suggests bacterial (not viral) aetiology — palpate the preauricular node in every red eye patient
Any red eye with photophobia must have the cornea thoroughly assessed with fluorescein and a cobalt blue filter before attributing the presentation to conjunctivitis — uveitis and keratitis must be excluded
A sexually active adult with “chronic conjunctivitis” that fails topical antibiotics should be tested for Chlamydia — inclusion conjunctivitis is significantly under-diagnosed in primary care; a careful sexual history is mandatory
Hyperacute onset with copious pus in any age group must be treated as gonococcal until proven otherwise — the potential for corneal perforation within hours means immediate referral takes priority over awaiting culture results
Do not prescribe topical aminoglycosides long-term — prolonged use of gentamicin or tobramycin causes significant ocular surface toxicity and may mask chronic chlamydial or herpetic disease

Azari AA, Barney NP. Conjunctivitis: a systematic review of diagnosis and treatment. JAMA. 2013;310(16):1721–1729.
Høvding G. Acute bacterial conjunctivitis. Acta Ophthalmol. 2008;86(1):5–17.
Rose PW, Harnden A, Brueggemann AB, Perera R, Sheikh A, Crook D, et al. Chloramphenicol treatment for acute infective conjunctivitis in children in primary care: a randomised double-blind placebo-controlled trial. Lancet. 2005;366(9479):37–43.
Sheikh A, Hurwitz B. Topical antibiotics for acute bacterial conjunctivitis: Cochrane systematic review and meta-analysis update. Br J Gen Pract. 2005;55(521):962–964.
Rietveld RP, ter Riet G, Bindels PJ, Bink D, Sloos JH, van Weert HC. The treatment of acute infectious conjunctivitis with fusidic acid: a randomised controlled trial. Br J Gen Pract. 2005;55(521):924–930.
O’Brien TP, Jeng BH, McDonald M, Raizman MB. Acute conjunctivitis: truth and misconceptions. Curr Med Res Opin. 2009;25(8):1953–1961.
Bhatt U, Lagnado R, Dua HS. Follicular conjunctivitis. Clin Exp Ophthalmol. 2005;33(3):296–301.
Centers for Disease Control and Prevention. Sexually transmitted infections treatment guidelines, 2021: Gonococcal infections. MMWR Recomm Rep. 2021;70(4):1–187.
Kowalski RP, Karenchak LM, Romanowski EG. Infectious disease: changing antibiotic susceptibility. Ophthalmol Clin North Am. 2003;16(1):1–9.
Uchio E, Takeuchi S, Itoh N, Matsuura N, Ohno S, Aoki K. Clinical and epidemiological features of acute follicular conjunctivitis with special reference to that caused by herpes simplex virus type 1. Br J Ophthalmol. 2000;84(9):968–972.
Woodland RM, Darougar S, Thaker U, Cornell L, Siddiqui N, Wania M, et al. Causes of conjunctivitis and keratoconjunctivitis in Karachi, Pakistan. Trans R Soc Trop Med Hyg. 1992;86(3):317–320.
Everitt H, Little P, Smith PW. A randomised controlled trial of management strategies for acute infective conjunctivitis in general practice. BMJ. 2006;333(7563):321.
Smith AF, Waycaster C. Estimate of the direct and indirect annual cost of bacterial conjunctivitis in the United States. BMC Ophthalmol. 2009;9:13.
Bhargava A, Jackson TL. Neonatal conjunctivitis. In: Taylor & Hoyt’s Pediatric Ophthalmology and Strabismus. 5th ed. Edinburgh: Elsevier; 2017:126–132.
Leibowitz HM. The red eye. N Engl J Med. 2000;343(5):345–351.
Cronau H, Kankanala RR, Mauger T. Diagnosis and management of red eye in primary care. Am Fam Physician. 2010;81(2):137–144.
Singapore Optometric Association. Scope of practice guidelines for optometrists in Singapore. Singapore: Singapore Optometric Association; 2022.

Clinical Illustration

Overview

Etiology