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Red Eye

(Pink Eye)


Christopher J. Brady

, MD, Wilmer Eye Institute, Retina Division, Johns Hopkins University School of Medicine

Last full review/revision May 2021| Content last modified May 2021
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Red eye refers to a red appearance of the opened eye, reflecting dilation of the superficial ocular vessels.


Dilation of superficial ocular vessels can result from

  • Infection

  • Allergy

  • Inflammation (noninfectious)

  • Elevated intraocular pressure (less common)

Several ocular components may be involved, most commonly the conjunctiva, but also the uveal tract, episclera, and sclera.


The most common causes of red eye include

Corneal abrasions and foreign bodies are common causes (see table Some Causes of Red Eye). Although the eye is red, patients usually present with a complaint of injury, eye pain, or both. However, in young children and infants, this information may be unavailable.


Some Causes of Red Eye


Suggestive Findings

Diagnostic Approach

Conjunctival disorders and episcleritis*

Bilateral, prominent itching, possibly conjunctival bulging (chemosis)

Known allergies or other features of allergies (eg, seasonal recurrences, rhinorrhea)

Sometimes use of topical ophthalmic drugs (particularly neomycin)

Clinical evaluation

Chemical (irritant) conjunctivitis

Exposure to potential irritants (eg, dust, smoke, ammonia, chlorine, phosgene)

Clinical evaluation

Unilateral focal redness, mild irritation, minimal lacrimation

Clinical evaluation

Infectious conjunctivitis

Scratchy sensation, photosensitivity

Sometimes mucopurulent discharge, eyelid edema, or papillae on tarsal conjunctiva

Clinical evaluation

Unilateral, asymptomatic focal red patch or confluent redness

Possibly prior trauma or Valsalva maneuver

Often history of use of anticoagulants or antiplatelet drugs (eg, aspirin, NSAIDs, warfarin)

Clinical evaluation

Intense itching, stringy discharge

Usually preadolescent or adolescent males

Other atopic disorders

Waxing in spring and waning in winter

Clinical evaluation

Corneal disorders†

Contact lens keratitis

Prolonged wearing of contact lenses, lacrimation, corneal edema

Clinical evaluation

Onset after injury (but this history may be inapparent in infants and young children)

Foreign body sensation

Lesion on fluorescein staining

Clinical evaluation

Often grayish opacity on the cornea, followed by a visible crater

Possibly a history of sleeping with contact lenses

Culture of ulcer (scrapings done by an ophthalmologist)

Epidemic keratoconjunctivitis (adenoviral conjunctivitis with keratitis), if moderate or severe

Copious watery discharge

Often eyelid edema, preauricular lymphadenopathy, chemosis (bulging of the conjunctiva)

Occasionally severe temporary loss of vision

Punctate pattern on fluorescein staining

Clinical evaluation

Onset after conjunctivitis, blisters on eyelid

Classic dendritic corneal lesion on fluorescein staining


Clinical evaluation

Viral culture if diagnosis is unclear

Unilateral vesicles and crusts on an erythematous base in a V1 distribution, sometimes affecting the tip of the nose

Eyelid edema

Red eye

May be associated with uveitis

Possibly severe pain

Clinical evaluation

Viral culture if diagnosis is unclear

Other disorders

Severe ocular ache

Headache, nausea, vomiting, halos around lights

Hazy cornea (caused by edema), marked conjunctival erythema

Decreased visual acuity

Intraocular pressure usually > 40 mm Hg

Tonometry and gonioscopy by ophthalmologist

Ocular ache, photophobia

Ciliary flush (redness most concentrated and often confluent around the cornea)

Often a risk factor (eg, autoimmune disorder, blunt trauma within previous few days)

Possibly decreased visual acuity or pus in anterior chamber (hypopyon)

Cells and flare on slit-lamp examination

Clinical evaluation

Severe pain, often described as boring

Photophobia, lacrimation

Red or violaceous patches under bulbar conjunctiva

Scleral edema

Tenderness of globe when palpated

Often history of autoimmune disorder

Clinical evaluation

Further testing by or in conjunction with an ophthalmologist

* Unless otherwise described, usually characterized by itching or scratchy sensation, lacrimation, diffuse redness, and often photosensitivity, but no change in vision and absence of pain and true photophobia.

† Unless otherwise described, usually characterized by lacrimation, pain, and true photophobia. Vision affected if the lesion involves the visual axis.

NSAIDS = nonsteroidal anti-inflammatory drugs; V1= ophthalmic division of the trigeminal nerve.


Most disorders can be diagnosed by a general health care practitioner.


History of present illness should note the onset and duration of redness and presence of any change in vision, itching, scratchy sensation, pain, or discharge. Nature and severity of pain, including whether pain is worsened by light (photophobia), are noted. The clinician should determine whether discharge is watery or purulent. Other questions assess history of injury, including exposure to irritants and use of contact lenses (eg, possible overuse, such as wearing them while sleeping). Prior episodes of eye pain or redness and their time patterns are elicited.

Review of systems should seek symptoms suggesting possible causes, including headache, nausea, vomiting, and halos around lights (acute angle-closure glaucoma); runny nose and sneezing (allergies, upper respiratory infection); and cough, sore throat, and malaise (upper respiratory infection).

Past medical history includes questions about known allergies and autoimmune disorders. Drug history should specifically ask about recent use of topical ophthalmic drugs (including over-the-counter drugs), which might be sensitizing.

Physical examination

General examination should include head and neck examination for signs of associated disorders (eg, upper respiratory infection, allergic rhinitis, zoster rash).

Eye examination involves a formal measure of visual acuity and usually requires a penlight, fluorescein stain, and slit lamp.

Best corrected visual acuity is measured. Pupillary size and reactivity to light are assessed. True photophobia (sometimes called consensual photophobia) is present if shining light into an unaffected eye causes pain in the affected eye when the affected eye is shut. Extraocular movements are assessed, and the eye and periorbital tissues are inspected for lesions and swelling. The tarsal surface is inspected for papillae. The corneas are stained with fluorescein and examined with magnification. If a corneal abrasion is found, the eyelid is everted and examined for hidden foreign bodies. Inspection of the ocular structures and cornea is best done using a slit lamp. A slit lamp is also used to examine the anterior chamber for cells, flare, and pus (hypopyon). Ocular pressure is measured using tonometry, although it may be permissible to omit this test if there are no symptoms or signs suggesting a disorder other than conjunctivitis.

Red flags

The following findings are of particular concern:

  • Sudden, severe pain and vomiting

  • Zoster rash

  • Decreased visual acuity

  • Corneal crater

  • Branching, dendritic corneal lesion

  • Ocular pressure > 40 mm Hg

  • Failure to blanch with phenylephrine eye drop

Interpretation of findings

Conjunctival disorders and episcleritis are differentiated from other causes of red eye by the absence of pain, photophobia, and corneal staining. Among these disorders, episcleritis is differentiated by its focality, and subconjunctival hemorrhage is usually differentiated by the absence of lacrimation, itching, and photosensitivity. Clinical criteria do not accurately differentiate viral from bacterial conjunctivitis.

Corneal disorders are differentiated from other causes of red eye (and usually from each other) by fluorescein staining. These disorders also tend to be characterized by pain and photophobia. If instillation of an ocular anesthetic drop (eg, proparacaine 0.5%), which is done before tonometry and ideally before fluorescein instillation, completely relieves pain, the cause is probably limited to the cornea. If pain is present and is not relieved by an ocular anesthetic, the cause may be anterior uveitis, glaucoma, or scleritis. Because patients may have anterior uveitis secondary to corneal lesions, persistence of pain after instillation of the anesthetic does not exclude a corneal lesion.

Anterior uveitis, acute angle-closure glaucoma, and scleritis can usually be differentiated from other causes of red eye by the presence of pain and the absence of corneal staining. Anterior uveitis is likely in patients with pain, true photophobia, absence of corneal fluorescein staining, and normal intraocular pressure; it is definitively diagnosed based on the presence of cells and flare in the anterior chamber. However, these findings may be difficult for general health care practitioners to discern. Acute angle-closure glaucoma can usually be recognized by the sudden onset of its severe and characteristic symptoms, but tonometry is definitive.

Pearls & Pitfalls

  • If pain persists despite an ocular anesthetic in a patient with a normal fluorescein examination, consider anterior uveitis, scleritis, or acute angle-closure glaucoma.

Instillation of phenylephrine 2.5% causes blanching in a red eye unless the cause is scleritis. Phenylephrine is instilled to dilate the pupil in patients needing a thorough retinal examination. However, it should not be used in patients who have the following:


Testing is usually unnecessary. Viral cultures may help if herpes simplex or herpes zoster is suspected and the diagnosis is not clear clinically. Corneal ulcers are cultured by an ophthalmologist. Gonioscopy is done in patients with glaucoma. Testing for autoimmune disorders may be worthwhile in patients with uveitis and no obvious cause (eg, trauma). Patients with scleritis undergo further testing as directed by an ophthalmologist.


The cause is treated. Red eye itself does not require treatment. Topical vasoconstrictors are not recommended.

Key Points

  • Most cases are caused by conjunctivitis.

  • Pain and true photophobia suggest other more serious diagnoses.

  • In patients with pain, slit-lamp examination with fluorescein staining and tonometry are key.

  • Persistence of pain despite an ocular anesthetic in a patient with a normal fluorescein examination suggests anterior uveitis, scleritis, or acute angle-closure glaucoma.

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