Conjunctivitis — Bacterial Viral Allergic

Bacterial Conjunctivitis—Acute Inflammation via Direct Invasion

• Bacterial pathogens breach the conjunctival epithelial barrier through direct inoculation or hematogenous spread, triggering acute neutrophilic inflammation
• Gram-positive bacteria (Staphylococcus aureus, Streptococcus pneumoniae) and gram-negative organisms (Haemophilus influenzae, Neisseria gonorrhoeae) colonize the conjunctival surface and multiply rapidly
• Bacterial virulence factors (lipopolysaccharides, exotoxins, proteases) activate the complement cascade via the alternative and classical pathways, generating C3a and C5a anaphylatoxins
• These chemotactic factors recruit polymorphonuclear leukocytes (PMNs) to the conjunctiva, resulting in dense neutrophilic infiltration and purulent exudate production
• The acute inflammatory response manifests clinically as chemosis, papillary hypertrophy, and copious mucopurulent discharge within 24-48 hours of infection
• Bacterial lipopolysaccharides and peptidoglycan directly upregulate conjunctival epithelial expression of IL-6, IL-8, and TNF-α, perpetuating inflammation and recruitment of additional immune cells
• In cases of Neisseria gonorrhoeae (a particularly virulent organism), the bacteria produce IgA protease and exhibit significant invasive potential, risking rapid corneal penetration and ulceration if untreated

Viral Conjunctivitis—Epithelial Damage and Host Immune Response

• Viral particles infect conjunctival epithelial cells, hijacking cellular machinery for replication and triggering innate immune responses
• Adenoviruses (most common viral cause) and enterovirus 70 cause cell lysis with release of damage-associated molecular patterns (DAMPs) that activate pattern recognition receptors (TLRs) on epithelial cells and antigen-presenting cells
• Infected epithelial cells produce type I interferons (IFN-α and IFN-β) via the RIG-I/MAVS signaling pathway, establishing an antiviral state in neighboring cells
• The resulting inflammatory infiltrate is predominantly lymphocytic and mononuclear (in contrast to bacterial conjunctivitis), with CD8+ T cells and natural killer cells driving cytotoxic elimination of infected cells
• Viral replication within epithelial cells causes focal epithelial necrosis and exfoliation, generating subepithelial infiltrates that appear clinically as follicles on the palpebral conjunctiva
• Herpes simplex virus (HSV) and varicella-zoster virus (VZV) additionally establish latency in sensory ganglia, with potential for recurrent disease triggered by stress, immunosuppression, or solar exposure
• The membrane-damaging nature of some viruses (particularly HSV) can compromise the epithelial barrier, leading to keratitis if viral replication extends to the cornea
• Enterovirus 70 (and less commonly other enterovirus serotypes) causes acute hemorrhagic conjunctivitis characterized by subconjunctival hemorrhages from microvascular damage rather than true bleeding diathesis

Allergic Conjunctivitis—Type I Hypersensitivity and IgE-Mediated Responses

• Allergic conjunctivitis represents a Type I hypersensitivity reaction initiated when environmental allergens (pollens, dust mites, animal dander, contact lens solution preservatives) cross-link IgE antibodies bound to mast cell and basophil surfaces on the conjunctival surface and in underlying mucosa
• IgE cross-linking triggers immediate degranulation of mast cells and basophils, releasing preformed inflammatory mediators including histamine, tryptase, heparin, and chondroitin sulfate
• Histamine acts on H1 and H2 receptors on conjunctival epithelial cells and blood vessels, causing vasodilation, increased vascular permeability, itching (via sensory nerve stimulation), and the characteristic mild conjunctival chemosis
• Mast cell activation also triggers synthesis and release of newly generated mediators: leukotrienes (LTC4, LTD4, LTE4), prostaglandins (PGD2), and platelet-activating factor (PAF)
• Leukotrienes amplify the inflammatory response by recruiting eosinophils and neutrophils; PAF activates platelets and increases adhesion molecule expression on endothelial cells
• Eosinophilic infiltration of the conjunctiva is characteristic, particularly in vernal keratoconjunctivitis (a chronic allergic condition predominantly in children), where eosinophil-derived major basic protein and eosinophil peroxidase cause epithelial damage
• Th2-polarized T cell responses (producing IL-4, IL-5) perpetuate chronic allergic inflammation, explaining the seasonal or perennial nature of symptoms depending on allergen exposure patterns
• The mechanism drives the hallmark clinical triad: pruritus, conjunctival hyperemia, and eyelid edema, with minimal exudate

Bacterial Conjunctivitis

• Staphylococcus aureus (including methicillin-resistant strains—MRSA): Most common cause of bacterial conjunctivitis in adults in developed countries; spreads via direct contact with contaminated fingers, eye makeup, or contact lens cases. Produces diverse virulence factors including alpha-toxin and Panton-Valentine leukocidin (PVL).

• Streptococcus pneumoniae: Second most common bacterial cause in many populations; often associated with concurrent sinusitis or respiratory infection. Historically more prevalent than S. aureus in some regions but has decreased with pneumococcal vaccination; still a significant cause of neonatal and pediatric conjunctivitis.

• Haemophilus influenzae (nontypable strains, previously type b before Hib vaccination): Gram-negative organism historically very common, now declining in vaccinated populations. Often causes acute suppurative conjunctivitis with significant exudate.

• Neisseria gonorrhoeae: Sexually transmitted pathogen; causes hyperacute bacterial conjunctivitis (1-3 days after exposure) with severe purulent exudate, intense inflammation, and risk of rapid corneal penetration and perforation if untreated. Acquired via direct contact during vaginal delivery in neonates (ophthalmia neonatorum) or in sexually active adults through genital-to-eye contact. Produces IgA protease and possesses high invasive potential.

• Neisseria meningitidis: Less common; typically causes hemorrhagic conjunctivitis with subconjunctival hemorrhages; requires suspicion of concurrent meningitis.

• Pseudomonas aeruginosa: Particularly associated with contact lens wearers, especially those with poor hygiene or extended-wear lenses. Gram-negative organism with multiple virulence factors; causes fulminant infection with risk of keratitis and corneal ulceration.

• Risk factors for bacterial conjunctivitis: Poor hand hygiene, contact lens use (especially non-compliance with cleaning protocols), recent eye trauma or surgery, hospitalization (nosocomial transmission), crowded living conditions (daycares, schools), concurrent upper respiratory infection.

Viral Conjunctivitis

• Adenovirus (serotypes 3, 7, 19, 37 most common): Causes epidemic keratoconjunctivitis (EKC) and pharyngoconjunctival fever (PCF). Most common viral cause globally. Highly contagious via respiratory droplets and direct eye contact; outbreaks occur in healthcare settings and schools. Serotypes 3 and 7 cause systemic symptoms; serotypes 19 and 37 cause ocular-only disease.

• Enterovirus 70 and Coxsackievirus A24: Cause acute hemorrhagic conjunctivitis characterized by subconjunctival hemorrhages, rapid onset, and short incubation period (12-48 hours). Primarily in tropical and subtropical regions; spread via fomites and close contact.

• Herpes simplex virus (HSV-1 and HSV-2): Causes herpetic keratoconjunctivitis with unilateral presentation, vesicular lid involvement, and significant risk of corneal involvement (dendritic ulcers). HSV-1 associated with recurrent labial herpes; HSV-2 with genital herpes. Risk of neonatal infection if maternal infection at delivery.

• Varicella-zoster virus (VZV): Presents with conjunctivitis in context of chickenpox (varicella) or shingles (herpes zoster ophthalmicus). Recurrent disease possible due to reactivation in sensory ganglia; zoster ophthalmicus associated with dermatomal distribution and vesicular rash on eyelids.

• Measles virus: Presents with Koplik spots (pathognomonic white spots on buccal mucosa) preceding measles rash; conjunctivitis develops simultaneously with systemic symptoms. Now rare in vaccinated populations.

• Epstein-Barr virus (EBV), Cytomegalovirus (CMV): Less common causes; CMV particularly relevant in immunocompromised hosts, potentially causing keratitis or scleritis. EBV-associated conjunctivitis occurs in infectious mononucleosis.

• Risk factors for viral conjunctivitis: Upper respiratory infection prodrome, systemic viral illness, immunocompromised status (for HSV reactivation, CMV), recent eye trauma, close contact with infected individuals, poor hand hygiene.

Allergic Conjunctivitis

• Seasonal allergic conjunctivitis (SAC): Triggered by seasonal environmental allergens (tree, grass, weed pollens in spring/summer). Most common type of allergic conjunctivitis; predominantly affects children and young adults.

• Perennial allergic conjunctivitis (PAC): Year-round symptoms due to constant allergen exposure (dust mites, animal dander, household molds). Often milder than SAC.

• Vernal keratoconjunctivitis (VKC): Chronic allergic inflammation predominantly in children and adolescents in warm climates; more common in males and in populations with darker skin. Characterized by giant papillae on palpebral conjunctiva ("cobblestone" appearance) and possible shield ulcers.

• Atopic keratoconjunctivitis (AKC): Chronic allergic disease in adults with atopic dermatitis or other atopic conditions. Associated with fibrosis and potential vision loss.

• Contact lens-related allergic conjunctivitis: Reaction to lens solution preservatives (particularly thimerosal and chlorhexidine) or to lens material itself. Improved with preservative-free solutions or switching lens types.

• Topical medication reactions: Allergic response to ophthalmic medications, especially antiglaucoma agents (prostaglandin analogs, beta-blockers), antibiotics, or preservatives in eye drops.

• Risk factors for allergic conjunctivitis: Personal or family history of atopy, environmental allergen exposure, contact lens use, warm climate residence (for VKC/AKC), male gender and darker skin (for VKC).

Cardinal Symptoms and Physical Findings Common to All Types

• Conjunctival injection (hyperemia): Blanching of the bulbar and palpebral conjunctiva due to vasodilation; appears as red discoloration. Bacterial infections typically show diffuse hyperemia including the limbus; viral may show sectoral or perilimbal injection; allergic shows less intense hyperemia with preserved clarity of small vessels.

• Discharge: Character and volume vary by etiology. Bacterial causes produce copious mucopurulent or purulent discharge (thick, yellowish-green, often matting eyelids closed, especially after sleep). Viral causes produce watery to mucoid discharge (typically scant, serous nature). Allergic produces mucoid discharge (stringy, ropy) with minimal suppuration.

• Chemosis: Conjunctival edema with subconjunctival fluid accumulation. Most prominent in bacterial conjunctivitis (particularly gonococcal) and allergic conjunctivitis; present but mild in viral cases.

• Eyelid edema: Swelling of palpebral and periorbital tissues. Prominent in allergic conjunctivitis (where it may be the predominant symptom); present in acute bacterial infection; minimal in uncomplicated viral disease.

Bacterial Conjunctivitis—Specific Features

• Acute onset: Symptoms develop over hours to 1-2 days; rapid progression characteristic of Neisseria gonorrhoeae (hyperacute presentation within 24-48 hours with severe symptoms).

• Papillary response: Upper tarsal conjunctiva shows papillary hypertrophy (small, red nodules representing vascular and inflammatory infiltrates on conjunctival epithelium overlying tarsal plate). Distinguishes from follicular response; papillae indicate acute inflammation.

• Unilateral vs bilateral: Often unilateral initially, but frequently becomes bilateral within days due to poor hand hygiene. Gonococcal infection may present acutely unilateral.

• Preauricular lymphadenopathy: Uncommon in bacterial conjunctivitis (though may occur); presence suggests viral or chlamydial etiology.

• Corneal involvement risk: Significant risk with N. gonorrhoeae and P. aeruginosa; presents with pain, photophobia, and decreased visual acuity if keratitis develops. Gonococcal infection can progress to corneal ulceration and scarring within hours to days.

Viral Conjunctivitis—Specific Features

• Prodrome of upper respiratory symptoms: Cough, rhinorrhea, pharyngitis, fever preceding ocular symptoms by several days, particularly in adenoviral infection (pharyngoconjunctival fever).

• Follicular response: Lower palpebral conjunctiva (and sometimes tarsal conjunctiva) displays follicles—small, dome-shaped elevations representing lymphoid aggregates (germinal centers) of CD8+ T cells and B cells. Develops over several days and peaks at 1-2 weeks. Viral hallmark.

• Subepithelial infiltrates (SEI): Fine, dust-like opacities in Bowman's layer of cornea, appearing as faint anterior stromal haze. Develop in 1-2 weeks post-infection and resolve slowly over weeks to months. Characteristic of adenoviral EKC; may persist and cause photophobia and mild visual disturbance.

• Preauricular or cervical lymphadenopathy: Common with viral conjunctivitis; helps distinguish from bacterial (where it is rare). Particularly present in adenoviral infection.

• Unilateral or bilateral: Often begins unilaterally but progresses to bilateral within 2-3 days due to autoinoculation.

• Hemorrhagic conjunctivitis: Subconjunctival hemorrhages (bright red or dark blood beneath conjunctiva) characteristic of enterovirus 70 and coxsackievirus A24; dramatic appearance but self-limited. Bleeding occurs from microvascular injury, not coagulopathy.

• Herpetic keratoconjunctivitis-specific features: Unilateral vesicular or ulcerative lid lesions with crusting; dendrite or ulcer on cornea (branching epithelial defect that stains with fluorescein); photophobia and pain prominent if corneal involvement.

• Duration: Viral conjunctivitis typically lasts 7-14 days for adenoviral disease; 2-4 weeks for full resolution

Initial evaluation (every red eye)

• Visual acuity: the single most important first measurement; conjunctivitis should not reduce corrected acuity. Loss of acuity means the cornea, uvea, or lens is involved.
• Penlight/slit-lamp exam with fluorescein: look for ciliary flush (perilimbal injection sparing the fornices), corneal opacity or epithelial defect, hypopyon, and pupillary irregularity — all point away from simple conjunctivitis.
• Lid eversion: follicles (pale lymphoid domes, viral/chlamydial) versus papillae (fibrovascular, bacterial/allergic) versus giant cobblestone papillae (vernal). Pseudomembranes suggest severe adenoviral or streptococcal disease.
• Palpate for preauricular nodes: tender node favors adenovirus or chlamydia.

When to test

• Gram stain and culture (blood, chocolate, and Thayer–Martin agar): mandatory for hyperacute copious purulent discharge, neonates, and any corneal involvement. Gram-negative intracellular diplococci in neutrophils establish Neisseria gonorrhoeae presumptively — treat immediately, do not wait for culture.
• Nucleic acid amplification testing (NAAT) of conjunctival and genital specimens is the confirmatory standard for gonococcal and chlamydial disease per CDC STI guidance; co-testing for the other organism is routine.
• Giemsa-stained conjunctival scraping: basophilic intracytoplasmic inclusion bodies in chlamydia; neutrophils in bacterial disease; mononuclear cells in viral; eosinophils support allergic conjunctivitis.
• Point-of-care adenoviral antigen immunoassay may confirm epidemic keratoconjunctivitis when outbreak control matters.
• Tonometry and dilated exam if angle-closure glaucoma or uveitis is in the differential.

Emergencies treated before anything else

• Gonococcal conjunctivitis: sight-threatening. Per the CDC 2021 STI Treatment Guidelines, adults receive a third-generation cephalosporin — ceftriaxone 1 g IM as a single dose — plus copious saline lavage of the fornices and same-day ophthalmology involvement. Presumptively treat chlamydial co-infection with doxycycline. Neonates receive single-dose parenteral ceftriaxone (cefotaxime substituted when hyperbilirubinemia or calcium-containing IV fluids are present).
• Neonatal chlamydial conjunctivitis: oral macrolide (erythromycin base) for 14 days; topical therapy alone is inadequate because the nasopharynx is colonized and pneumonia can follow.
• Herpetic keratoconjunctivitis with a fluorescein-staining dendrite: topical antiviral (ganciclovir gel or trifluridine) or oral acyclovir with urgent ophthalmology referral.

Contraindicated

• Topical corticosteroids started empirically — they worsen HSV to geographic ulceration and raise intraocular pressure.
• Topical anesthetics dispensed for home use — epithelial toxicity and corneal melt.
• Eye patching in infectious conjunctivitis, and contact lens wear until symptom-free.
• Chronic topical vasoconstrictors — rebound hyperemia (conjunctivitis medicamentosa).

Ophthalmic emergencies

• Gonococcal corneal ulceration and perforation: N. gonorrhoeae penetrates intact corneal epithelium, and IgA protease plus neutrophil collagenases melt the stroma within 24–48 hours. Signals: worsening pain, corneal haze or infiltrate, hypopyon, or acuity loss in a hyperacute purulent eye. Requires admission-level urgency and same-day ophthalmology.
• Pseudomonas keratitis in a contact lens wearer: proteases and exotoxin A drive rapid stromal necrosis; a white corneal infiltrate with an epithelial defect in a lens wearer is an emergency until cultured.
• HSV stromal keratitis and geographic ulcer: immune-mediated stromal inflammation, often precipitated by inadvertent topical steroids; leads to scarring and neurotrophic cornea. Hutchinson sign (vesicles on the nasociliary-supplied nasal tip) in herpes zoster ophthalmicus predicts intraocular involvement — uveitis, and rarely acute retinal necrosis.

Disease-related, non-emergent

• Adenoviral subepithelial infiltrates: delayed cell-mediated response to viral antigen in Bowman's layer; produce glare and blurred vision persisting weeks to months.
• Pseudomembranes and symblepharon: fibrin-rich exudate organizes into conjunctival adhesions and cicatrization after severe epidemic keratoconjunctivitis.
• **Trachoma (chronic C. trachomatis serovars A–C)**: repeated infection scars the tarsus → entropion and trichiasis → corneal opacification; the leading infectious cause of blindness worldwide.
• Vernal shield ulcer: eosinophil major basic protein toxicity to the superior cornea; oval sterile epithelial defect with photophobia.
• Atopic keratoconjunctivitis: chronic scarring, keratoconus, and cataract.
• Systemic extension: chlamydial neonatal pneumonia (afebrile, staccato cough, eosinophilia); meningococcal conjunctivitis carries risk of invasive meningococcal disease.

Treatment-related

• Topical corticosteroids: steroid-response ocular hypertension, posterior subcapsular cataract, and reactivation of HSV or fungal keratitis.
• Oral erythromycin in infants under six weeks: association with infantile hypertrophic pyloric stenosis — counsel about nonbilious projectile vomiting.
• Aminoglycoside and benzalkonium-preserved drops: epithelial toxicity mimicking persistent conjunctivitis.
• Ceftriaxone in neonates with hyperbilirubinemia: bilirubin displacement; cefotaxime is substituted.

• Itching is the discriminator for allergic disease: a stem emphasizing bilateral itching, stringy mucoid discharge, and cobblestone tarsal papillae in an atopic patient wants a topical antihistamine/mast-cell stabilizer (olopatadine), not an antibiotic.
• Tender preauricular lymphadenopathy plus watery discharge plus a recent URI equals adenovirus. Best next step is supportive care and hygiene counseling; adenovirus resists alcohol-based sanitizer and survives on surfaces, which is why clinic outbreaks are tested.
• Hyperacute, copious purulent discharge within 24–48 hours in a sexually active adult or a 2–5-day-old neonate is gonococcal until proven otherwise. Best next step: Gram stain and culture, then parenteral ceftriaxone plus saline lavage — this is the one conjunctivitis that perforates a cornea. Topical therapy alone is the classic wrong answer.
• Neonatal timing sequence: first 24 hours → chemical (historically silver nitrate); days 2–5 → gonococcal; days 5–14 → chlamydial. Erythromycin ointment at birth prevents gonococcal ophthalmia only; it does not prevent chlamydial conjunctivitis or pneumonia.
• Contact lens wearer with a red, painful eye: remove the lens, culture, and cover Pseudomonas with a topical fluoroquinolone. Never patch the eye and never prescribe a topical anesthetic for home use.
• **A branching dendritic ulcer on fluorescein means HSV.** Give an antiviral and refer; topical steroids convert it to a geographic ulcer. This is the most commonly tested contraindication in ophthalmology.
• Follicles versus papillae: follicles are avascular lymphoid domes (viral, chlamydial, or drug-induced); papillae have a central vascular tuft (bacterial, allergic). Vesicles on the tip of the nose (Hutchinson sign) predict ocular zoster.
• Common distractor: prescribing antibiotic drops for a clearly viral or allergic red eye. AAO explicitly discourages reflexive antibiotic use, and topical steroids should never be started without slit-lamp examination.