Conjunctivitis

Overview

• Inflammation of the conjunctiva, the vascular mucous membrane lining the inner eyelids and covering the sclera, from infectious (viral or bacterial) or noninfectious (allergic) causes.
• The most common cause of red eye, a frequent primary-care and urgent-care presentation in children and adults.
• This article covers general, non-neonatal disease: viral, bacterial, and allergic conjunctivitis. Neonatal conjunctivitis (onset in the first month of life) is a distinct entity, covered separately.
• Defining feature across all subtypes: conjunctival injection with discharge and normal visual acuity; pain, photophobia, or vision loss signal an alternative diagnosis, not simple conjunctivitis.

Epidemiology

• Viral etiology predominates overall, particularly in adults, and is most prevalent in summer; adenovirus is the most frequently implicated pathogen.
• Bacterial conjunctivitis is more common in children; adults more often have viral disease. It spreads by direct contact and may occur as a secondary infection after a viral episode.
• Allergic conjunctivitis can be seasonal or perennial and commonly coexists with other atopic disease (allergic rhinitis, asthma, eczema).
• Risk is amplified by overcrowding (schools, daycares, households) and exposure to infected persons or contaminated multidose eye-drop vials.

Risk factors

• Direct contact with an infected person or contaminated fomites: shared towels, pillows, cosmetics, or multidose eye-drop bottles; overcrowded settings.
• Concurrent or recent upper respiratory infection: viral conjunctivitis frequently occurs with a URI.
• Contact lens wear: raises suspicion for keratitis whenever conjunctivitis-like symptoms occur; requires discontinuing lens use.
• Personal or family history of atopy: hay fever, asthma, and eczema.
• Sexual activity and unprotected genital contact: risk for gonococcal or chlamydial (inclusion) conjunctivitis via autoinoculation.
• Health care or congregate-living work: raises bacterial transmission risk and informs antibiotic use.

Pathophysiology

• Viral conjunctivitis: inoculation of adenovirus (most common), coxsackievirus, or enterovirus causes a lymphocyte-predominant response with follicle formation and watery discharge; typically starts in one eye before spreading bilaterally by autoinoculation.
• Bacterial conjunctivitis: direct contact inoculation of gram-positive organisms (S. pneumoniae, viridans streptococci, H. influenzae, S. aureus) most commonly, producing a neutrophil-rich purulent exudate over 1-2 days.
• Hyperacute (gonococcal) conjunctivitis: Neisseria gonorrhoeae invades the conjunctival epithelium and can penetrate the intact cornea, producing rapidly progressive purulent discharge with risk of corneal ulceration, perforation, and vision loss within hours to days.
• Chlamydial (inclusion) conjunctivitis: Chlamydia trachomatis causes subacute mucopurulent conjunctivitis via autoinoculation from genital secretions, with basophilic intracytoplasmic inclusion bodies on Giemsa stain.
• Allergic conjunctivitis: an IgE-mediated type I hypersensitivity reaction; allergen cross-linking of mast-cell-bound IgE triggers degranulation and histamine release, producing itching, chemosis, and vascular congestion.

Clinical features

• Conjunctival injection with discharge and preserved visual acuity is the hallmark across all subtypes; true ocular pain, photophobia, or decreased vision is not expected and should prompt evaluation for keratitis, iritis, scleritis, or angle-closure glaucoma instead.
• Discharge character is the key discriminator among subtypes:
  • Viral: watery/serous discharge, irritation, foreign-body sensation, often with preauricular adenopathy and a recent URI; starts unilateral and becomes bilateral.
  • Bacterial (nongonococcal): thick, whitish-yellow mucopurulent discharge with crusting and lids matted shut on waking; no significant pain or preauricular adenopathy.
  • Allergic: bilateral, watery discharge with stringy white mucus, intense itching, chemosis, and often rhinorrhea; no infectious contact history.
• Hyperacute purulent onset is a distinguishing red flag for gonococcal disease: sudden onset with rapid progression over hours, copious purulent discharge, marked swelling, and significant pain; assume gonococcal until proven otherwise.
• Chlamydial (adult inclusion) conjunctivitis presents subacutely with mucopurulent, follicular conjunctivitis in a sexually active adult, more indolent than typical bacterial disease.
• Symptom-based clues help narrow the differential: itching suggests allergy; burning suggests a lid disorder or dry eye; foreign-body sensation suggests a foreign body; deep pain suggests scleritis, iritis, or acute glaucoma.
• Red flags requiring urgent ophthalmology evaluation: pain with eye movement, photophobia, decreased acuity, a corneal defect on fluorescein staining, a fixed pupil, and hyperpurulent discharge.

Differential diagnosis

• Bacterial keratitis: true ocular pain, photophobia, and a corneal infiltrate or opacity, often with contact lens wear, unlike the clear cornea and painless eye of conjunctivitis.
• Herpes simplex keratitis: foreign-body sensation, pain, blurred vision, and a dendritic corneal ulcer with terminal bulbs on staining, absent in conjunctivitis.
• Corneal abrasion: history of trauma or foreign body with pain and photophobia; fluorescein staining shows an epithelial defect, whereas conjunctivitis stains negative.
• Acute angle-closure glaucoma: sudden severe pain, headache, nausea, halos around lights, and a fixed mid-dilated pupil with elevated intraocular pressure, unlike the painless red eye of conjunctivitis.
• Episcleritis: sectoral or diffuse superficial redness with mild tenderness but no purulent or mucoid discharge; self-limited.
• Scleritis: deep, severe, boring pain that can wake the patient and a violaceous globe hue, unlike discharge-predominant conjunctivitis.
• Anterior uveitis (iritis): deep eye pain, photophobia, circumcorneal ciliary flush, and a small or irregular pupil, without the discharge typical of conjunctivitis.
• Orbital cellulitis or preseptal cellulitis: eyelid swelling and erythema; orbital disease additionally causes pain with eye movement, proptosis, and diplopia, all absent in conjunctivitis.
• Systemic disease with associated conjunctivitis: Kawasaki disease (bilateral nonexudative injection with fever, rash, mucositis) and reactive arthritis (conjunctivitis with urethritis, arthritis) carry systemic findings absent in isolated conjunctivitis.
• Subconjunctival hemorrhage: bright red, well-demarcated blood under the conjunctiva with normal vision and no discharge, unlike the diffuse injection and discharge of conjunctivitis.

Diagnosis

• Conjunctivitis is a clinical diagnosis made on history and slit-lamp or penlight examination of discharge character, laterality, onset, and preauricular nodes; no laboratory study is required for uncomplicated disease, but the specific etiology (viral, bacterial nongonococcal, gonococcal, chlamydial, or allergic) must be determined because management differs by subtype.
• First, assess for red flags suggesting a vision-threatening diagnosis: pain with eye movement, photophobia, decreased acuity, a corneal defect or opacity on fluorescein staining, and a fixed or irregular pupil; any should prompt same-day ophthalmology evaluation instead of empiric treatment.
• Next, classify by discharge and onset pattern: watery discharge with URI symptoms and preauricular adenopathy suggests viral; purulent discharge with crusted, matted lids over 1-2 days suggests bacterial; bilateral itching with watery, stringy discharge and an atopic history suggests allergic; sudden, rapidly progressive, copious purulent discharge with marked pain suggests gonococcal, a same-day ophthalmology emergency requiring immediate corneal examination for ulceration or perforation.
• Finally, reserve conjunctival Gram stain and culture, or nucleic acid amplification testing, for severe, chronic, or recurrent disease and suspected gonococcal or chlamydial infection.

Clinical pearl. Discharge character alone is the fastest bedside discriminator: watery points to viral, thick purulent to bacterial, and stringy mucoid with itching to allergic; sudden-onset copious purulent discharge with significant pain breaks this pattern and should be treated as gonococcal until excluded.

Management

• First, exclude sight-threatening red flags (pain with eye movement, photophobia, decreased acuity, corneal staining, hyperpurulent discharge); if present, refer emergently to ophthalmology instead of treating empirically.
• If viral conjunctivitis is suspected (watery discharge, concurrent URI, preauricular adenopathy), treat with cold compresses and artificial tears only; antibiotics are not indicated, and symptoms typically resolve within 1-2 weeks. Advise hand hygiene and avoidance of towel/pillow sharing given high contagiousness.
  • If symptoms fail to improve, or herpes simplex is suspected (eyelid vesicles, dendritic corneal lesion), refer to ophthalmology.
• If nongonococcal bacterial conjunctivitis is suspected (purulent discharge, matted lids, no significant pain), use cold compresses; 65% improve within 2-5 days without antibiotics, so withholding therapy is reasonable in a patient who is not immunocompromised, contact-lens-wearing, or health-care-employed.
  • When treatment is chosen, give a topical antibiotic for 5-7 days: preferably polymyxin B/trimethoprim ophthalmic drops, 1 drop 4 times daily.
    • Erythromycin 0.5% ophthalmic ointment, a thin ribbon to the lower conjunctival sac 4 times daily, is an equivalent alternative.
    • Ciprofloxacin 0.3% ophthalmic drops, 1-2 drops 4-6 times daily, is required in a contact lens wearer (who should also stop lens use), because the first two agents lack reliable Pseudomonas coverage.
  • If there is no improvement within 3 days, refer to ophthalmology.
• If gonococcal (hyperacute) conjunctivitis is suspected (sudden onset, copious purulent discharge, marked pain, rapid progression), treat as a medical emergency because corneal involvement can cause blindness.
  • Obtain emergency ophthalmology consultation, irrigate the eye with saline, and examine the cornea for ulceration or perforation.
  • Give ceftriaxone 500 mg IM as a single dose (1 g IM if body weight over 150 kg).
  • Add doxycycline 100 mg PO twice daily for 7 days to cover coinfecting chlamydia unless excluded.
• If chlamydial (adult inclusion) conjunctivitis is suspected (subacute mucopurulent discharge in a sexually active adult, confirmed by NAAT or Giemsa stain), treat with azithromycin 1 g PO as a single dose, or doxycycline 100 mg PO twice daily for 7 days as an alternative, and treat sexual partners.
• If allergic conjunctivitis is suspected (bilateral itching, watery/stringy discharge, atopic history), first remove or avoid the offending allergen when identifiable and use cold compresses.
  • Start olopatadine 0.2% ophthalmic solution, 1 drop once daily, as first-line pharmacotherapy through the exposure period; topical antibiotics are not used for allergic disease.
  • If a pure mast-cell stabilizer is preferred, use cromolyn sodium 4% ophthalmic solution, 1-2 drops 4 times daily, counseling that up to 14 days may be needed for full effect.
  • If refractory to first-line topical therapy, add loteprednol 0.2% ophthalmic suspension, 1 drop 4 times daily, as a short course under close ophthalmology supervision because of glaucoma, cataract, and corneal damage risk with prolonged use.

Complications

• Corneal ulceration, scarring, or perforation: the principal threat with gonococcal conjunctivitis and any conjunctivitis with corneal involvement; can cause permanent vision loss if treatment is delayed.
• Endophthalmitis: intraocular spread of infection requiring immediate intravenous antibiotics and ophthalmologic evaluation.
• Chronic or recurrent conjunctivitis: from inadequately treated chlamydial infection, incomplete allergen avoidance, or an unrecognized alternative diagnosis (blepharitis, dry eye).
• Transmission to close contacts: viral and bacterial disease are highly contagious, with outbreaks in schools and households.
• Disseminated gonococcal infection: untreated ocular gonococcal disease can reflect or progress to systemic dissemination.

Prognosis

• Viral conjunctivitis is self-limited, resolving within 1-2 weeks in most patients; a minority develop subepithelial corneal infiltrates with blurred vision for weeks.
• Nongonococcal bacterial conjunctivitis resolves without antibiotics in most patients (65% improve within 2-5 days); antibiotics shorten the course but are not required for cure.
• Allergic conjunctivitis follows a chronic, relapsing course tied to allergen exposure, with good control from topical therapy plus avoidance, though symptoms recur with re-exposure.
• Gonococcal conjunctivitis has a good visual prognosis when treated emergently before corneal perforation, but delayed treatment risks permanent vision loss.
• Chlamydial conjunctivitis responds well to azithromycin or doxycycline; partner treatment prevents reinfection.

Prevention

• Hand hygiene and avoidance of fomite sharing: avoid sharing towels, pillows, cosmetics, or eye drops during an active episode to limit transmission.
• Avoid multidose eye-drop vial contamination: do not let the dropper tip touch the eye or skin, a recognized risk factor for bacterial outbreaks.
• Discontinue contact lens use with any red eye until symptoms and discharge fully resolve and the eye has been evaluated, to prevent progression to keratitis.
• Screen and treat sexual partners of a patient with gonococcal or chlamydial conjunctivitis with the regimens used for genital infection (ceftriaxone 500 mg IM single dose and/or azithromycin 1 g PO single dose or doxycycline 100 mg PO twice daily for 7 days, per pathogen).
• Start topical therapy before the season: in known seasonal allergic conjunctivitis, beginning olopatadine 0.2% once daily before the expected season blunts peak severity.
• Exclude infectious conjunctivitis patients from school or daycare while active purulent discharge is present, given high contagiousness.

Key points

• Discharge pattern is the fastest bedside discriminator: watery favors viral, thick purulent favors bacterial, stringy mucoid with itch favors allergic, and copious hyperacute purulent discharge with pain favors gonococcal emergency.
• Preserved visual acuity and absence of true pain define uncomplicated conjunctivitis; pain, photophobia, or vision loss should trigger evaluation for keratitis, iritis, scleritis, or acute glaucoma instead.
• Most nongonococcal bacterial conjunctivitis resolves without antibiotics (65% improve within 2-5 days), so withholding antibiotics is reasonable in a low-risk, immunocompetent, non-contact-lens-wearing patient.
• Gonococcal conjunctivitis is a same-day ophthalmology emergency requiring systemic ceftriaxone plus empiric chlamydia coverage given the risk of rapid corneal perforation.
• First-line allergic conjunctivitis therapy is a topical antihistamine/mast-cell-stabilizer drop (olopatadine once daily); topical corticosteroids are reserved for refractory cases under ophthalmology supervision.
• Neonatal conjunctivitis (ophthalmia neonatorum) is a distinct entity with different pathogens, timing, and prophylaxis, covered in its own article.