Subconjunctival hemorrhage—widely referred to as “red eye”—is the most common ocular problem seen by primary-care clinicians. Red eye refers to hyperemia of the superficially visible vessels of the conjunctiva (the mucous membrane lining the inner eyelids and part of the eyeball), sclera (the dense, opaque “white of the eye” that protects the eyeball), or episclera (the connective tissue between the conjunctiva and the sclera).1

Conjunctivitis accounts for most cases of red eye encountered in primary care. (Although commonly referred to as “pink eye,” the conjunctiva becomes red.) Instead of conjunctivitis, however, these patients may have hordeolum (which includes styes), orbital cellulitis, dacryocystitis, corneal abrasion, or a foreign body in the eye. Red-eye conditions that can cause vision loss include corneal inflammation (keratitis), acute iritis (uveitis—inflammation of the uvea, which consists of the iris, the ciliary body, and the choroid), and acute angle-closure glaucoma.

Patient history may point to cause

The clinician should ask patients with red eye about their chief complaint; the severity of pain on a scale of 0-10; timing issues as related to the onset, duration, frequency, and progression of  symptoms; and associated symptoms.2 Inquire about discharge from the eyes within the previous 12 hours, blurred vision, eye pain, sensitivity to light (photophobia), seeing colored halos around lights, itchy eyes, eyelids that feel “glued” closed in the morning, chest infection, fever, and neck tenderness or swelling. These symptoms can help identify the cause of red eye.

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A history of red eye in family members or other close contacts suggests possible conjunctivitis. If the patient has pets at home or has had recent exposure to other animals, the eye problem could be a sign of allergies. Conjunctivitis, longstanding red eye that has persisted despite treatment, or the presence of seasonal allergies can indicate allergic conjunctivitis, corneal abrasion, or iritis.

The patient’s medical history can provide other clues to the cause of red eye. For example, the use of diuretics or a history of collagen vascular disease can lead to dry eyes, which can in turn cause red eye, as in the case of keratoconjunctivitis sicca. This condition results from any decrease in tear production. Recent sexually transmitted infection (STI) could indicate bacterial conjunctivitis, which can be caused by chlamydia and gonorrhea. The STI must be treated immediately to prevent permanent damage to the patient’s vision.

Eye charts are part of the physical exam

The clinician should check a person with red eye for general discomfort, photophobia, or proptosis—an abnormal, bulging protrusion of one or both eyeballs. Use the Rosenbaum or Snellen eye chart to determine whether the patient’s visual acuity is normal. Decreased visual acuity suggests a serious ocular condition, such as keratitis, iridocyclitis (inflammation of the iris and ciliary body), or glaucoma.

Next, inspect the eyelid for inflammation, redness, or pain (blepharitis); determine whether the eyelashes are evenly distributed and whether the base of the eyelashes is inflamed; and examine the conjunctiva and sclera for conjunctival discharge.  If such discharge is present, note whether it is scant or profuse, purulent, mucopurulent, or serous. Distinguish among subconjunctival hemorrhage, conjunctival hyperemia (engorgement of the larger and more superficial bulbar vessels), and ciliary flush (injection of the deep conjunctival and episcleral vessels surrounding the cornea). Bear in mind that these conditions can exist alone or in combination.1 

Using a penlight to check pupil size (larger or smaller than the usual diameter of 2-6 mm), shape (regular or irregular), and reaction to light (sluggish or nonreactive) and the cornea for large keratic precipitates, irregular surface, or corneal reflections can help differentiate red eye (Table 1). For example, conjunctivitis does not affect the pupil. If the patient has one pupil that is smaller than the other, the diagnosis is iridocyclitis. Limitation of eye movement may be seen with orbital cellulitis that has affected cranial nerves III, V, and VI. 

Conduct an ophthalmoscopic examination with either the standard or the panoptic ophthalmoscope. If you suspect a corneal abrasion or disruption of the corneal epithelium, perform a fluorescein eye stain, which detects corneal ulcers, corneal lesions, and foreign bodies; any abnormalities will stain bright green. If a corneal lesion is revealed, refer the patient to an ophthalmologist.

If no obvious infection is present, using tonometry to measure intraocular pressure (IOP) can help confirm the diagnosis of acute angle-closure glaucoma (elevated IOP). Do not perform tonometry screening if an external infection is obvious.

Specific diagnoses and treatments

Conjunctivitis (Figure 1), which is defined as hyperemia of the conjunctival blood vessels, often is not a serious condition. It can have bacterial, viral, allergenic, or irritative causes. In bacterial conjunctivitis, the etiology may be Staphylococcus aureus, Streptococcus pneumoniae, Hemophilus influenzae, or Neisseria gonorrhoeae.
Conjunctivitis causes intensely itchy eyes, tearing, redness, mucous discharge, eyelids that stick together, and the sensation of a foreign body in the eye. An upper respiratory infection is often associated with bacterial conjunctivitis.

Conjunctivitis can be bilateral but usually is seen unilaterally. Diagnostic tests include visual acuity; culture when the patient is a contact-lens wearer or when bacterial infection is suspected, or Gram’s stain of discharge if gonococcus is suspected; and fluorescein staining.

Therapy for conjunctivitis includes cool compresses applied to the eye four times a day. Instruct the patient to avoid smoke, dry wind, and sun exposure; discard eye makeup; and discontinue contact-lens use. For viral nonherpetic conjunctivitis, treatment with a vasoconstrictor/antihistamine (naphazoline/pheniramine) four times a day to relieve severe itching or topical treatment, such as a ½-inch of erythromycin ophthalmic ointment twice a day for five days, may be used. Also effective is two drops of 10% sulfacetamide ophthalmic drops every four hours for five days. Herpetic conjunctivitis should be treated with one drop of trifluridine 1% five to six times a day, vidarabine 3% ointment five times a day, or oral acyclovir 200 mg five times a day. Gonorrheal conjunctivitis should be treated with ceftriaxone 1 g IM one time and a ½-inch of bacitracin ophthalmic ointment four times a day. Bacterial conjunctivitis is treated for seven days with either ciprofloxacin drops four times a day or erythromycin ointment four times a day. Show the patient how to use drops and ointments properly.

Differential diagnoses for conjunctivitis include episcleritis, scleritis, uveitis, acute angle-closure glaucoma, corneal ulcer, and foreign body.3

Hordeolum (Figure 2) is an acute or subacute inflammation or bacterial infection of the glands or hair follicles in the eyelids. It can be external (stye) or internal (chalazion), causing pain until the hordeolum ruptures or drains. Symptoms include redness at the margin of the eyelid, with scaling and collection of discharge and localized inflammation of the base of the eyelashes. Typically, the patient reports that the lid’s redness and swelling are worst in the morning. Slit-lamp examination of eyelid margins will reveal plugged meibomian glands.

A warm compress for 15-20 minutes three times a day may help with the pain and aid drainage of the hordeolum. An incision also may help drain the hordeolum, thereby reducing pain and speeding recovery. Erythromycin ophthalmic ointment applied to the eyelid can prevent the spread of the infection. Doxycycline, minocycline, erythromycin, or dicloxacillin is used for resistant cases. Artificial tears may benefit dry eyes. Instruct the patient on the correct use of drops and ointments, proper eyelid hygiene, and the importance of prompt treatment to avoid recurrence.

Differential diagnoses for hordeolum include eyelid abscess, allergic or contact dermatitis, herpes simplex, and cellulitis of the eyelid.4

Orbital cellulitis is an inflammatory response associated with orbital trauma or infection, dental abscess, or upper respiratory infection.5  More than 60% of cases develop from infection of the ethmoid sinuses. The causative agents may be staphylococci or streptococci.

Patients will have pain or redness in the orbital area, swelling, pressure, tearing,eyelid redness, blurred vision, diplopia (double vision), and/or exophthalmos (ocular proptosis) due to inflammation or decreased vision. The clinician should perform an ocular evaluation and order a complete blood count as well as a culture of the ocular material. CT or MRI may be needed if the eye is too swollen for ocular exam.

Treatment options for orbital cellulitis include warm compresses to the eye, parenteral antibiotics, or incision and drainage of the abscess or infected area.

Differential diagnoses include allergic reaction, Graves’ disease, orbital mucocele, and neoplasms.
Dacryocystitis (Figure 3) is an infection of the lacrimal sac, caused by obstruction of the nasolacrimal system. It can be acute or chronic. Dacryocystitis is usually unilateral and occurs most often in infants and in persons older than age 40.6 A patient with acute dacryocystitis presents with pain, swelling, tenderness, and redness in the tear sac. A patient with a chronic case will have tearing and discharge (mucus or purulent material may be expelled). In adults, acute infection is due to Staphylococcus aureus or, occasionally, b-hemolytic streptococci.

Dacryocystitis is confirmed by applying pressure on the lacrimal sac and expressing drainage (mucus or purulent material) from the punctum, the opening in the lacrimal drainage system located in each eyelid. The pus should be collected and sent for Gram’s stain smear and culture.

A warm compress three to four times a day, gentle massage of the punctum, and/or systemic antibiotics (cephalexin or amoxicillin-clavulanate) may be used to treat acute dacryocystitis. In chronic cases, a topical antibiotic is needed; some cases may require incision and drainage of the abscess. The patient should have a follow-up appointment in one to three days.

Differential diagnoses for dacryocystitis include chalazion, facial and orbital cellulitis, sinus tumors, and ethmoid sinusitis.

Corneal abrasion (Figure 4) is a loss of corneal surface epithelial tissue resulting from trauma.4 The patient presents with blurred vision, photophobia, sharp pain, foreign-body sensation in the eye, watery eye, and/or discharge. Corneal abrasions are diagnosed by checking visual acuity, inspecting the eye, and then applying fluorescein stain to visualize changes in the epithelial lining. Cobalt blue light or Wood’s lamp can be used for visualization.

Treatment should begin early with an antibiotic ointment or topical/systemic nonsteroidal anti-inflammatory drugs (NSAIDs). Artificial tears may alleviate some of the symptoms. Eye patches are not indicated. Teach the patient how to use drops and ointments and how to prevent further abrasions, e.g., by handling contact lenses properly.
The eye should be rechecked in 24 hours. In most cases, the corneal abrasion will heal within 24-48 hours after the initiation of treatment. Refer the patient to an ophthalmologist if there is no response to treatment or if the infection spreads.5

Differential diagnoses for corneal abrasion include acute angle-closure glaucoma, herpes ulcers, other corneal ulcers, and a foreign body in the cornea.4

Acute iritis or iridocyclitis (uveitis) (Figure 5) is an inflammation of the iris or the iris and ciliary body. It is often manifested by ciliary flush, which is considered serious.3 Patients with uveitis typically present with bilateral or unilateral achy eye pain, redness, significant photophobia, blurred vision, or floaters (a dead cell or cell fragment or other optical debris perceived as a spot in the visual field). Other physical findings include retinal irritation and decreased papillary responses. Patients may have a history of autoimmune, connective tissue, or infectious disease. Slit-lamp and funduscopic examination should be performed. Prompt treatment with short-acting mydriatic drops (1% tropicamide) dramatically reduces the photophobia and pain, facilitating examination.3 Topical steroids or NSAIDs also relieve symptoms.

Immediate referral to an ophthalmologist can prevent blindness in a person with uveitis.3 The clinician should explain the condition to the patient and emphasize the importance of following up with an ophthalmologist.

Differential diagnoses include glaucoma, conjunctivitis, retinal detachment, retinopathy, keratitis, scleritis, and episcleritis.4

Acute angle-closure glaucoma (Figure 6) occurs when outflow of the aqueous humor (the fluid between the cornea and the crystalline lens) is blocked. It frequently results in an intraocular pressure (IOP) that is elevated beyond the normal level of 10-21 mm Hg.5 The patient reports visual field loss, seeing halos around lights, and a sudden unilateral ocular pain or headache. Older adults may experience nausea, vomiting, or abdominal discomfort, sometimes leading to a misdiagnosis of appendicitis.

Patients usually seek treatment immediately because of the extreme pain. On examination, the eye appears red and acutely inflamed. When acute angle-closure glaucoma is suspected, the person may need tests in addition to an ophthalmoscopic evaluation: IOP measurement (usually >50 mm Hg, producing a hard eye on palpation), gonioscopy (revealing a closed angle), slit-lamp examination (steamy or cloudy, edematous cornea), and observation of pupils (fixed, mid-dilated). Also, the anterior chamber is shallow, as revealed by holding a penlight laterally and directing it nasally. In an eye with a narrow angle or shallow anterior chamber, a shadow is cast on the nasal side of the iris.6

The goal of treatment is preventing vision loss through a 20% reduction in IOP. This can be accomplished with acetazolamide 500 mg IV, followed by 250 mg by mouth four times a day. Some patients may require incision of the iris (iridotomy) to maintain IOP reductions or laser therapy to the peripheral iris (iridoplasty). Pilocarpine 4% (one drop every 15 minutes for one hour and then four times a day) can be used once IOP is below 50 mm Hg, to continue to lower the pressure. The patient should be informed of the importance of medication adherence and ophthalmology follow-up.

Differential diagnoses include temporal arteritis, acute iritis, corneal ulcer, and other causes of red eye (conjunctivitis, trauma, scleritis, keratitis, foreign body, or allergies).


Primary-care clinicians should be prepared to recognize, diagnose, and treat the less serious causes of red eye. Be sure to establish a working relationship with a local ophthalmologist for emergency situations.

Ms. Danforth is assistant professor and associate director at the Clinical Learning Center at Florida State University College of Medicine in Tallahassee.

1. Bradford CA, ed. Basic Ophthalmology for Medical Students and Primary Care Residents. 7th ed. San Francisco, Calif.: American Academy of Ophthalmology; 1999: 58-76.

2. Kiesler J. The red eye. In: Steele D, Susman J, McCurdy F, eds. Student Guide to Primary Care: Making the Most of Your Early Clinical Experience, Philadelphia, Pa.: Hanley and Belfus; 2003:281-284.

3. Red eye. MD Consult Preview. December 20, 2006. Available at:, accessed July 8, 2008.

4. Ferri FF. 2006 Ferri’s Clinical Advisor: Instant Diagnosis and Treatment, St. Louis, Mo.: Mosby; 2005:221.
5. Davis A, ed. Adult Nurse Practitioner Certification Review. St. Louis, Mo.: Mosby; 2001:491-515.

6. Riordan-Eva P. Disorders of the eyes and lids. In: McPhee SJ, PapadakisMA, Tierney LM Jr, eds. Current Medical Diagnosis & Treatment 2008, New York, N.Y.: McGraw-Hill Medical; 2008:141-167.