Making the Diagnosis

To accurately assess and diagnose this patient’s condition, the clinician needs to eliminate other possible causes of symptoms. Conjunctivitis, which is the most common form of eye infection, usually presents with more diffuse redness, is usually bilateral, and is accompanied by discharge. Keratitis can mimic conjunctivitis; however, conjunctival injection or hyperemia is typically most pronounced at the limbus. Iritis may also produce conjunctival injection at the limbus. Episcleritis is usually an acute infection without pain that will blanch with application of a topical vasoconstrictor (phenylephrine) and will become numb with use of a topical anesthetic.


Scleritis is a rare cause of a painful red eye that can be distinguished from conjunctivitis by the following features: it is typically unilateral and the eye is tender to palpation through the eyelid.  There is usually no relief of pain with topical anesthetics and no blanching of the redness if topical vasoconstrictors are used. Unlike keratitis or iritis, scleritis typically presents with a peripheral location of redness and no photophobia. Vision is typically preserved.

If scleritis is suspected, the patient should be started on oral and or topical nonsteroidal anti-inflammatory drugs (NSAIDs). The patient should receive an urgent referral to ophthalmology for treatment with topical steroids if the diagnosis is confirmed as well as efforts to determine a primary cause, many of which will require additional disease-specific treatments.

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Conjunctivitis is the most common cause of red eye; however, when a patient’s eye condition does not fit the criteria for conjunctivitis it is critical to evaluate the patient for the less common causes of red eye and refer to ophthalmology.

Brady Pregerson, MD, is an emergency physician at Tri-City Medical Center and Scripps Coastal Urgent Care both in Oceanside, California.


Pregerson DB. Ophthalmology. Red Eye. Emergency Medicine 1-Minute Consult. 5th ed. 2017;5.