Red Eye: A Merck Manual of Patient Symptoms podcast

Red eye refers to a red appearance of the opened eye, reflecting dilation of the superficial ocular vessels.

Pathophysiology

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.

Etiology

The most common causes of red eye include

• Infectious conjunctivitis
• Allergic conjunctivitis

Corneal abrasions and foreign bodies are common causes (see Table 11: Symptoms of Ophthalmologic Disorders: 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.

Table 11
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Some Causes of Red Eye Cause Suggestive Findings Diagnostic Approach Conjunctival disorders and episcleritis* Allergic or seasonal conjunctivitis 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 Episcleritis Unilateral focal redness, mild irritation, minimal lacrimation Clinical evaluation Infectious conjunctivitis Scratchy sensation, photosensitivity Sometimes mucopurulent discharge, eyelid edema, or follicles on tarsal conjunctiva Clinical evaluation Subconjunctival hemorrhage 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 Vernal conjunctivitis 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 Corneal abrasion or foreign body Onset after injury (but this history may be inapparent in infants and young children) Foreign body sensation Lesion on fluorescein staining Clinical evaluation Corneal ulcer 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 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 Herpes simplex keratitis Onset after conjunctivitis, blisters on eyelid Classic dendritic corneal lesion on fluorescein staining Unilateral Clinical evaluation Viral culture if diagnosis is unclear Herpes zoster ophthalmicus 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 Acute angle-closure glaucoma 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 Anterior uveitis 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 Scleritis 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. V1 = ophthalmic division of the trigeminal nerve. Some Causes of Red Eye Cause Suggestive Findings Diagnostic Approach Conjunctival disorders and episcleritis* Allergic or seasonal conjunctivitis 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 Episcleritis Unilateral focal redness, mild irritation, minimal lacrimation Clinical evaluation Infectious conjunctivitis Scratchy sensation, photosensitivity Sometimes mucopurulent discharge, eyelid edema, or follicles on tarsal conjunctiva Clinical evaluation Subconjunctival hemorrhage 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 Vernal conjunctivitis 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 Corneal abrasion or foreign body Onset after injury (but this history may be inapparent in infants and young children) Foreign body sensation Lesion on fluorescein staining Clinical evaluation Corneal ulcer 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 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 Herpes simplex keratitis Onset after conjunctivitis, blisters on eyelid Classic dendritic corneal lesion on fluorescein staining Unilateral Clinical evaluation Viral culture if diagnosis is unclear Herpes zoster ophthalmicus 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 Acute angle-closure glaucoma 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 Anterior uveitis 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 Scleritis 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. V1 = ophthalmic division of the trigeminal nerve.

Evaluation

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

History

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, URI); and cough, sore throat, and malaise (URI).

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

Physical examination

General examination should include head and neck examination for signs of associated disorders (eg, URI, 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 follicles. 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 skin 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, glaucoma, 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.

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:

• Suspected acute angle-closure glaucoma
• A history of angle-closure glaucoma
• A narrow anterior chamber

Testing

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.

Treatment

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. These diagnoses should not be missed.

Last full review/revision November 2012 by Kathryn Colby, MD, PhD