What is Conjunctivitis?

Conjunctivitis is an eye condition characterized by inflammation and redness of the conjunctiva, the outer membrane of the eye.  The condition is most often caused by allergies, viruses, or bacterial infection.  Individuals usually experience eye redness, itchiness, and irritation.  Occasionally, the eye will feel as if there is sand in it.

Severe causes of red eye that can lead to visual loss include keratitis, iritis, and acute angle-closure glaucoma.  These conditions require emergent referral to an eye specialist (ophthalmologist).

What Causes Conjunctivitis?

Conjunctivitis caused by inflammation of the conjunctiva.  The conjunctiva is a translucent membrane that lines the front of the sclera and inner eyelids.  The bulbar part of the conjunctiva covers the visible part of the sclera and the palpebral part of the conjunctiva covers the inner eyelids.  Various factors such as environmental allergens (e.g., pollen, animal dander), viruses, or bacterial infection can lead to irritation and inflammation of the conjunctiva.  This causes blood vessels in the conjunctiva to dilate, ultimately resulting in eye redness (hyperemia) and discharge.  Viral and bacterial conjunctivitis are very contagious.

How Common is Conjunctivitis?

In the United States, an estimated 1% of primary care visits are related to conjunctivitis.  About 70% of individuals with conjunctivitis go to their primary care provider or urgent care.  Advanced cases of the condition may require referral to an ophthalmology specialist, particularly if first-line treatment was unsuccessful.

Viral infection is the most common cause of conjunctivitis and is more frequent in the summer.  Bacterial infection is the second most common etiology – this is responsible for approximately 50%-75% of cases in children. The most common bacterial organisms include H. influenzae, S. pneumoniae, S. aureus, and Moraxella catarrhalis.  Worldwide, C. trachomatis keratoconjunctivitis is responsible for up to 8% of the population.  Allergic conjunctivitis occurs in about 15%-40% of cases of conjunctivitis and is more common in the spring and summer.

Signs and Symptoms

The symptoms of conjunctivitis usually depend on the underlying cause.  Bacterial conjunctivitis is normally characterized by a purulent discharge at the lid margins seen throughout the day.  It most often affects one eye, but both eyes are occasionally infected.  Individuals with Neisseria gonorrhea infection frequently develop a rapidly progressive and severe conjunctivitis that can threaten eye sight.

Viral conjunctivitis normally causes eye redness, clear or mucous discharge, and burning in one eye.  The second eye usually becomes involved within 24-48 hours.  Individuals may have associated viral symptoms such as fever, body aches (myalgias), diarrhea, and headache.  Patients can develop preauricular lymphadenopathy – swelling and tenderness of the lymph nodes in front of the ear.  Symptoms often worsen for the first 5 days, then gradually improve after 1-2 weeks.

Patients with allergic conjunctivitis usually experience redness in both eyes, itchiness, and watery discharge.  Itchiness is a key distinguishing factor between allergic conjunctivitis and other forms of the disease.  Individuals often have coexisting seasonal allergies and asthma.

All of these forms of conjunctivitis may result in the eyes being stuck closed in the morning.


The diagnosis of conjunctivitis is suggested based on symptoms, history, and physical examination.  The diagnosis is highly suggested in an individual with red eye and discharge who has no visual changes or evidence of keratitis, iritis, or angle closure glaucoma.  These later conditions often lead to significant eye pain and loss of vision, and are considered eye emergencies that requires urgent ophthalmologic evaluation.

Your doctor will perform a detailed eye examination – this includes eye inspection, pupillary light reflex testing, extraocular movement assessment, visual acuity testing with the Snellen chart, visual field examination, and funduscopic examination.  If your eyes have pus draining from them, your doctor may send a sample to the laboratory for gram stain and culture.  This is normally done in individuals with recurrent or refractory cases of bacterial conjunctivitis.

Conjunctivitis Medication and Treatment

The treatment of conjunctivitis depends on its cause.  Bacterial conjunctivitis is normally treated with topical antibiotics such as:

  • Erythromycin 5 mg/g ophthalmic ointment
  • Trimethoprim-polymyxin B 0.1%-10,000 units/mL drops
  • Ofloxacin 3% drops
  • Ciprofloxacin 3% drops

Children, individuals with poor medical compliance, or those who experience trouble administering eye drops should use ointmentOintment may temporarily cause blurriness for about 20 minutes after administration.  Fluoroquinolones such as ciprofloxacin are preferred in individuals who wear contact lenses.

Viral conjunctivitis has no specific treatment.  Patients may have symptomatic relief with the use of topical antihistamine/decongestants or from lubricating agents.

Allergic conjunctivitis is normally treated with allergen avoidance and general measures such as the avoidance of eye rubbing, discontinuation of contact lens use during symptomatic episodes, application of cool compresses over the eyes, and use refrigerated artificial tears as needed.

Short term (< 2 weeks) use of topical antihistamine/vasoconstrictor preparations can be beneficial.  These include Naphcon-A, Opcon-A, or Visine-A (naphazoline HCl/pheniramine maleate).  Individuals with more than 2 episodes per month and those with perennial allergic disease often receive one of the following topical agents:

  • Patanol (olopatadine)
  • Alrex (loteprednol etabonate)
  • Lastacaft (alcaftadine)
  • Bepreve (bepotastine)
  • Optivar (azelastine HCl)
  • Elestat (epinastine)
  • Ketotifen (ketotifen fumarate)

These medications have antihistamine and mast cell stabilizing properties.  Antihistamines may worsen symptoms in patients with underlying dry eye.  Patients with refractory allergic conjunctivitis are occasionally referred to an allergy specialist for consideration of allergen immunotherapy.



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  2. Erdinest N, Solomon A. Topical immunomodulators in the management of allergic eye diseases. Curr Opin Allergy Clin Immunol 2014; 14:457.
  3. Leibowitz HM. The red eye. N Engl J Med 2000; 343:345.

The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.