Conjunctivitis is a common inflammation of the bulbar and/or palpebral conjunctiva. It can be classified into infectious (mostly viral) and noninfectious conjunctivitis, which includes allergic causes. Patients commonly present with red eyes, increased tearing, burning, foreign body sensation, and photophobia. Itching is a chief symptom in allergic conjunctivitis. Treatment depends on the underlying cause and includes antibiotic and antiviral therapy, glucocorticoids, and antihistamines.

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Epidemiology and Etiology


  • Most common non-traumatic eye complaint
  • Estimated incidence in the United States is 6 million people per year 
  • Most frequently found in infants, school-age children, and the elderly


Infectious conjunctivitis

  • Viral 
    • Adenoviruses (most common cause, 65%–90% of cases)
    • Herpes simplex virus (most common cause in children and infants)
    • Varicella-zoster virus (most common in the elderly)
    • Picornavirus (enterovirus and coxsackievirus cause acute hemorrhagic conjunctivitis)
    • Molluscum contagiosum (causes chronic follicular conjunctivitis)
    • HIV (usually affects posterior segment of the eye)
  • Bacterial 
    • Staphylococcus aureus (most common cause in adults)
    • Streptococcus pneumoniae
    • Haemophilus influenzae (most common cause in children)
    • Moraxella catarrhalis
    • Neisseria gonorrhoeae (more common in newborns) or Neisseria meningitidis 
    • Chlamydia trachomatis
    • Gram-negative enteric flora

Noninfectious conjunctivitis

  • Allergic (e.g., from airborne allergens)
  • Nonallergic (e.g., “dry eye syndrome,” associated with blepharitis, Sjögren’s syndrome, reactive arthritis)

Clinical Presentation

Patients can present with some or all of the following symptoms:

  • Hyperemia of the conjunctiva with injection of blood vessels (classic “pink eye” appearance)
  • Watery eyes or excessive tearing
  • Swelling of the eyelids and conjunctiva (chemosis)
  • Discharge and crust formation (varies depending on etiology)
  • Itching, burning, or foreign-body sensation in the eye
  • Photophobia 
  • Normally reactive pupils with normal visual acuity (important for differential diagnoses!)
Viral conjunctivitisBacterial conjunctivitisAllergic conjunctivitis
DischargeClear, watery dischargeThick, purulent yellow, white, or green discharge with severe crustingClear, watery discharge
Eye involvementBegins unilateral, but usually progresses to bilateral (highly infectious)Unilateral, can rarely progress to bilateralBilateral
Conjunctival appearanceMostly peripheral injection with conjunctival follicles (small swollen papules usually on the palpebral and bulbar conjunctiva)Diffuse injection, non-follicularDiffuse injection with chemosis and conjunctival follicles
Other symptomsExtraocular signs of viral infection (fever, lymphadenopathy, pharyngitis, rash)Signs of bacterial infection, depending on etiologySneezing, itching, atopic dermatitis
  • Punctate keratitis
  • Bacterial superinfection
  • Conjunctival scarring
  • Chronic dry eye
  • Corneal scars
  • Corneal ulcers
  • Corneal ulcers
  • Visual impairment
  • Otitis media
  • Meningitis
  • Cellulitis
  • Pneumonia (in infants)
  • Chronic conjunctivitis
  • Chronic dry eye


The diagnosis is mainly clinical.

  • Viral conjunctivitis: 
    • History of recent viral infection (not mandatory)
      • If symptoms are recurrent/chronic →  conjunctival smear, cultures, or viral isolation required 
      • Mononuclear cells and lymphocytes are seen on Giemsa stain of conjunctival scrapings.
  • Bacterial conjunctivitis:
    • If persistent or severe disease, diagnosis is uncertain, and in newborn conjunctivitis →  conjunctival scrapings, culture, or PCR required
    • Findings for various bacterial infections: 
      • Bacterial conjunctivitis shows a predominance of neutrophils on Giemsa staining
      • In gonococcal ophthalmia neonatorum, Gram stain of exudate shows gram-negative intracellular diplococci; culture in modified Thayer-Martin medium grows N. gonorrhoea.
      • In chlamydial conjunctivitis, Giemsa stain shows neutrophils with inclusion bodies and plasma cells.
  • Allergic conjunctivitis
    • Clinical history, signs and symptoms are usually sufficient.
    • Eye pain is not characteristic of allergic conjunctivitis, and more serious disorders must be ruled out, including angle-closure glaucoma, scleritis, or episcleritis.
    • If patient does not respond to therapy, referral to an opthalmologist is indicated, who may refer to an allergist for possible skin testing to detect the causative allergen(s).
  • In cases of visual impairment, significantly increased photophobia, inability to keep the eye open, abnormal pupil reaction to light, or severe headache with nausea, other diagnoses must be ruled out (and specialist referrals are indicated):
    • Glaucoma
    • Uveitis
    • Keratitis
    • Meningitis (especially in infants)


Viral conjunctivitis

  • Uncomplicated viral conjunctivitis is treated symptomatically. 
  • Antihistamine drops/artificial tears
  • Herpes simplex infection is treated with a topical antiviral (e.g., ganciclovir).

Bacterial conjunctivitis

  • Topical broad-spectrum antibiotics (e.g., erythromycin, trimethoprim-polymyxin B) 
  • Neisserial and chlamydial infections require systemic treatment
    • For gonococcal conjunctivitis, a single dose of intramuscular ceftriaxone plus oral azithromycin is given. Alternative agents are cefotaxime or ceftazidime.
    • For chlamydial neonatal conjunctivitis, oral erythromycin is preferred.
  • Prevention of ophthalmia neonatorum: prenatal maternal screening, systemic antibiotic treatment, and prophylaxis for newborns

Allergic conjunctivitis

  • Antihistamine drops/artificial tears
  • Oral antihistamines and mast-cell stabilizers (e.g., ketotifen)
  • Cold compresses
  • Nonsteroidal anti-inflammatory drugs (e.g., ketorolac)
  • Corticosteroids (e.g., fluorometholone)

Differential Diagnosis

The following conditions enter into the differential diagnoses of conjunctivitis:

  • Glaucoma: a condition caused by acutely or chronically increased intraocular pressure or — since up to 40% of those affected do not have increased IOP — there may be heightened ganglion susceptibility to normal pressure, problems with the microcirculation or extracellular matrix in the optic nerve
    Treatment includes surgery plus topical beta-blockers and prostaglandins. If left untreated, both the common open-angle and the less common angle-closure glaucoma can lead to blindness.
  • Uveitis: an ophthalmic emergency caused by the inflammation of the uvea, which includes the iris and ciliary body, the choroid. The cause can be either infectious (mostly viral) or noninfectious. Common symptoms include burning of the eye, redness, blurry vision, photophobia, floaters, and irregular pupils. Treatment includes topical or systemic steroids, antivirals, and topical atropine.
  • Keratitis: a mostly infectious acute or chronic inflammation of the cornea. Other causes include allergy and trauma. Patients commonly present with a red, teary painful eye, impaired vision, and photophobia. Treatment depends on the underlying condition and includes topical antivirals, antibiotics, and antifungals.
  • Meningitis (especially in infants): a potentially life-threatening inflammation of the leptomeninges, mostly due to viruses or bacteria. Common symptoms include headaches, fever, a stiff neck, altered mental status, photophobia, and phonophobia. Young children often present with nonspecific symptoms. Treatment consists of antibiotics, antivirals, and corticosteroids. 
  • Subconjunctival hemorrhage: This condition is usually asymptomatic. The clinical appearance, with demarcated areas of extravasated blood just beneath the surface of the eye, is generally both obvious and diagnostic. It may occur spontaneously or with Valsalva-associated mechanisms (e.g., coughing, sneezing, or vomiting). The diagnosis is confirmed by normal acuity and the absence of discharge, photophobia, or foreign body sensation. It typically resolves within 1 to 2 weeks.
  • Chalazion: presents as painless localized eyelid swelling and firm rubbery nodule. It is caused by the obstruction of Zeis or Meibomian glands.
  • Dry eye syndrome: a multifactorial disease of the ocular surface with loss of tear film and ocular symptoms, also known as keratoconjunctivitis sicca. Patients present with dryness and redness of the eye, general irritation, gritty/burning sensation, foreign body sensation, paradoxical excessive tearing, photophobia, or blurred vision. 
  • Blepharitis: an inflammation of the eyelid margin with eye irritation. Patients usually present with red, swollen or itchy eyelids; a gritty burning sensation; conjunctival injection; crusting and matting of the eyelashes in the morning; photophobia; and blurred vision.

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