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Overview of Conjunctivitis


Melvin I. Roat

, MD, FACS, Sidney Kimmel Medical College at Thomas Jefferson University

Last full review/revision Apr 2021| Content last modified Apr 2021
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Conjunctival inflammation typically results from infection, allergy, or irritation. Symptoms are conjunctival hyperemia and ocular discharge and, depending on the etiology, discomfort and itching. Diagnosis is clinical; sometimes cultures are indicated. Treatment depends on etiology and may include topical antibiotics, antihistamines, mast cell stabilizers, and corticosteroids.

Infectious conjunctivitis is most commonly viral conjunctivitis or bacterial conjunctivitis and is contagious. Rarely, mixed or unidentifiable pathogens are present. Numerous allergens can cause allergic conjunctivitis. Nonallergic conjunctival irritation can result from foreign bodies; wind, dust, smoke, fumes, chemical vapors, and other types of air pollution; and intense ultraviolet light of electric arcs, sunlamps, and reflection from snow.

Conjunctivitis is typically acute, but both infectious and allergic conditions can be chronic. Additional conditions that cause chronic conjunctivitis include ectropion, entropion, blepharitis, and chronic dacryocystitis.

Symptoms and Signs of Conjunctivitis

Any source of inflammation can cause lacrimation or discharge and diffuse conjunctival vascular dilation. Discharge may cause the eyes to crust overnight. Thick discharge may blur vision, but once discharge is cleared, visual acuity should be unaffected.

Itching and watery discharge predominate in allergic conjunctivitis. Chemosis and papillary hyperplasia also suggest allergic conjunctivitis. Irritation or foreign body sensation, photophobia, and discharge suggest infectious viral conjunctivitis; purulent discharge suggests bacterial conjunctivitis. Severe eye pain suggests scleritis.

Diagnosis of Conjunctivitis

  • Clinical evaluation

  • Sometimes culture

Usually, diagnosis of conjunctivitis is made by history and examination (see table Differentiating Features in Acute Conjunctivitis), usually including slit-lamp examination with fluorescein staining of the cornea and, if glaucoma is suspected, measurement of intraocular pressure. In order to prevent transmitting infection to other patients and to staff, meticulous disinfection of equipment that touches the eye is particularly important after examination of patients who could have conjunctivitis.

Other disorders can cause a red eye. Deep pain in the affected eye when a light is shone in the unaffected eye (true photophobia) does not occur in uncomplicated conjunctivitis and suggests a disorder of the cornea or anterior uvea. Circumcorneal conjunctival hyperemia (sometimes described as ciliary flush) is caused by dilated, fine, straight, deep vessels that radiate out 1 to 3 mm from the limbus, without significant hyperemia of the bulbar and tarsal conjunctivae. Ciliary flush occurs with uveitis, acute glaucoma, and some types of keratitis (see Corneal Disorders) but not with uncomplicated conjunctivitis.

Pearls & Pitfalls

  • Suspect another cause of red eye (eg, uveitis, glaucoma, keratitis) if patients have true photophobia, loss of vision, or ciliary flush and do not have significant discharge or tearing.

The cause of conjunctivitis is suggested by clinical findings. However, cultures are indicated for patients with severe symptoms, immunocompromise, a vulnerable eye (eg, after a corneal transplant, in exophthalmos due to Graves disease), or poor response to initial therapy.

Clinical differentiation between viral and bacterial infectious conjunctivitis is not highly accurate. However, if the history and examination strongly suggest viral conjunctivitis, withholding antibiotics initially is appropriate. Antibiotics can be prescribed later if the clinical picture changes or if symptoms persist.


Differentiating Features in Acute Conjunctivitis


Discharge/Cell Type

Eyelid Edema

Node Involvement


Purulent/polymorphonuclear leukocytes


Usually none


Clear/mononuclear cells


Often present


Clear, mucoid, ropy/eosinophils

Moderate to severe


Mild to intense

Treatment of Conjunctivitis

  • Prevention of spread

  • Treatment of symptoms

Most infectious conjunctivitis is highly contagious and spreads by droplets, fomites, and hand-to-eye inoculation. To avoid transmitting infection, physicians must

  • Use hand sanitizer or wash their hands properly (fully lather hands, scrub hands for at least 20 seconds, rinse well, and turn off the water using a paper towel)

  • Disinfect equipment after examining patients

Patients should do the following:

  • Use hand sanitizer and/or wash their hands thoroughly after touching their eyes or nasal secretions

  • Avoid touching the noninfected eye after touching the infected eye

  • Avoid sharing towels or pillows

  • Avoid swimming in pools

Eyes should be kept free of discharge and should not be patched. Small children with conjunctivitis should be kept home from school to avoid spreading the infection. Cool washcloths applied to the eyes may help relieve local burning and itching. Antimicrobials are used for certain infections.

Key Points

  • Conjunctivitis typically results from infection, allergy, or irritation.

  • Infectious conjunctivitis is usually highly contagious.

  • Typical findings are redness (without ciliary flush) and discharge, without significant pain or loss of vision.

  • Diagnosis is usually clinical.

  • Treatment includes measures to prevent spread and treatment of the cause (sometimes antimicrobials).

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