Eye redness refers to a red appearance of the normally white part of the eye. The eye looks red or bloodshot because blood vessels on the surface of the eye widen (dilate), bringing extra blood into the eye. Pink eye Infectious Conjunctivitis Infectious conjunctivitis is inflammation of the conjunctiva usually caused by viruses or bacteria. Bacteria and viruses can infect the conjunctiva. Redness and tearing or discharge are common... read more 
typically refers to eye redness caused by a specific viral infection.
Blood vessels can dilate as a result of
Infection
Allergy
Inflammation caused by something other than an infection
Elevated pressure inside the eye, typically caused by sudden, closed-angle glaucoma, in which fluid pressure increases in the front chamber of the eye
Several parts of the eye may be affected, most commonly the conjunctiva (the thin membrane that lines the eyelid and covers the front of the eye), but also the iris (the colored part of the eye), the sclera (the tough white fiber layer covering the eye), and the episclera (the connective tissue layer between the sclera and the conjunctiva).
An Inside Look at the Eye
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Rarely is eye redness the only eye symptom. People may have tearing, itching, the feeling that a foreign object is in the eye (foreign body sensation), sensitivity to light, pain, or even changes in vision. Sometimes people have symptoms that affect other areas of the body, such as a runny nose or cough, or nausea and vomiting.
Causes
Many disorders can cause eye redness. Some are emergencies, but others are mild and go away without treatment. The degree of redness does not indicate the seriousness of the disorder. The presence of eye pain or vision problems is more likely to suggest a serious cause.
The most common causes of eye redness are
Inflammation of the conjunctiva caused by an infection (infectious conjunctivitis, or pink eye Infectious Conjunctivitis Infectious conjunctivitis is inflammation of the conjunctiva usually caused by viruses or bacteria. Bacteria and viruses can infect the conjunctiva. Redness and tearing or discharge are common... read more
)Inflammation of the conjunctiva caused by an allergic reaction (allergic conjunctivitis Allergic Conjunctivitis Allergic conjunctivitis is inflammation of the conjunctiva caused by an allergic reaction. Allergic reactions caused by, for example, airborne allergens, may inflame the conjunctiva. Redness... read more
)
Scratches of the cornea Corneal Abrasions and Corneal Foreign Bodies Foreign bodies in the cornea cause abrasions, resulting in pain and redness, and lead to infections, even after they are removed. Most of these injuries are minor. (See also Overview of Eye... read more (the clear layer in front of the iris and pupil) and foreign objects in the eye Corneal Abrasions and Corneal Foreign Bodies Foreign bodies in the cornea cause abrasions, resulting in pain and redness, and lead to infections, even after they are removed. Most of these injuries are minor. (See also Overview of Eye... read more are also common causes of eye redness. In these cases, however, the person is more likely to consider the problem to be an eye injury, eye pain, or both. Corneal scratches may be caused by contact lenses or by foreign objects or tiny particles trapped under the eyelid. Occasionally, very dry air can cause some eye redness and irritation.
Serious causes of eye redness are much less common. They include corneal ulcers Corneal Ulcer A corneal ulcer is an open sore on the cornea (the clear layer in front of the iris and pupil) that is usually caused by an eye infection. Contact lenses, injuries, disorders, drugs, and nutritional... read more 
, herpes simplex keratitis Herpes Simplex Keratitis Herpes simplex keratitis is an eye infection that involves the cornea (the clear layer in front of the iris and pupil) and is caused by herpes simplex virus. The infection commonly recurs and... read more 
(herpes infection in the cornea), herpes zoster ophthalmicus Herpes Zoster Ophthalmicus Herpes zoster ophthalmicus is a reactivated infection of the eye caused by the varicella-zoster virus, the virus that causes chickenpox and shingles. Symptoms include pain and tingling of the... read more 
(shingles in or around the eye), acute closed-angle glaucoma Glaucoma Glaucomas are a group of eye disorders characterized by progressive optic nerve damage (often, but not always, associated with increased eye pressure) that can lead to irreversible loss of vision... read more , anterior uveitis Uveitis Uveitis is inflammation anywhere in the pigmented inside lining of the eye, known as the uvea or uveal tract. The uveal tract may become inflamed because of infection, injury, a bodywide autoimmune... read more , and scleritis Scleritis Scleritis is severe, destructive inflammation of the sclera (the tough, white, fiber layer covering the eye) that may threaten vision. Scleritis sometimes occurs in people who have a bodywide... read more (a deep, painful inflammation of the sclera).
Evaluation
Not every case of eye redness requires evaluation by a doctor. The following information can help people decide when to see a doctor and to know what to expect during an evaluation. In most cases, people with eye redness can be evaluated by a general health care practitioner rather than an ophthalmologist (a medical doctor who specializes in the evaluation and treatment—surgical and nonsurgical—of eye disorders).
Warning signs
In people with eye redness, certain symptoms and characteristics are cause for concern. They include
Sudden, severe pain and vomiting
Rash on the face, particularly around the eyes or on the tip of the nose
Decreased sharpness of vision (visual acuity)
An open sore on the cornea
When to see a doctor
Deep eye pain Eye Pain Eye pain may be severe and seem sharp, aching, or throbbing, or people may feel only mild irritation of the eye surface or the sensation of a foreign object in the eye (foreign body sensation)... read more should be distinguished from irritation. People who have warning signs, particularly deep pain or a change in vision, should see a doctor right away. If no warning signs are present, it is safe to wait a couple of days or so, but people may want to see a doctor sooner so that they can start treatment quickly.
What the doctor does
Doctors first ask questions about the person's symptoms and medical history and then do a physical examination. What they find during the history and physical examination often suggests a cause of eye redness and the tests that may need to be done (see table Some Causes and Features of Eye Redness Some Causes and Features of Eye Redness 
).
Doctors ask
How long redness has been present
Whether redness has occurred before
Whether there is pain or itching
Whether there is discharge or the eyes are tearing
Whether there is a change in vision
Whether there has been an eye injury
Whether the person wears contact lenses and whether they have been overused
Whether the person has been exposed to substances (such as dust or eye drops) that could irritate the eyes
Whether there are other symptoms (such as headache, halos around lights, runny nose, cough, or sore throat)
Whether the person has allergies
Pain together with nausea or vomiting or halos around lights is a potentially serious combination of symptoms. These symptoms often occur in acute closed-angle glaucoma Types of glaucoma Glaucomas are a group of eye disorders characterized by progressive optic nerve damage (often, but not always, associated with increased eye pressure) that can lead to irreversible loss of vision... read more . Pain and sensitivity to light may indicate a disorder of the cornea, such as a scratch or a foreign object. An absence of pain and sensitivity to light may indicate a disorder of the conjunctiva.
During the physical examination, doctors examine the head and neck for signs of disorders that may cause eye redness, such as runny nose and cough that may indicate an upper respiratory infection or allergy or a rash that may indicate shingles (herpes zoster infection).
The eye examination is the most important part of the physical examination. Doctors check the person's eye and the area around the eye for injuries or swelling. They check the person's vision (with glasses or contacts if the person wears them), pupil size and response to a light, and eye movement.
Doctors use a slit lamp What Is a Slit Lamp? 
(an instrument that enables a doctor to examine the eye under high magnification) to examine the eye. Doctors put a drop of anesthetic and then a drop of fluorescein stain in the eye to diagnose corneal disorders Introduction to Corneal Disorders The cornea is the clear layer in front of the iris and pupil. It protects the iris and lens and helps focus light on the retina. It is composed of cells, protein, and fluid. The cornea looks... read more . While the eye is anesthetized, pressure inside the eye (intraocular pressure) is often measured (called tonometry Tonometry A person who has eye symptoms should be checked by a doctor. However, some eye disorders cause few or no symptoms in their early stages, so the eyes should be checked regularly (every 1 to 2... read more ).
If pain develops in the affected eye (particularly if it is shut at this time) when a light is shined in the unaffected eye, the problem may be anterior uveitis Uveitis Uveitis is inflammation anywhere in the pigmented inside lining of the eye, known as the uvea or uveal tract. The uveal tract may become inflamed because of infection, injury, a bodywide autoimmune... read more or a corneal disorder. The use of an anesthetic makes the examination easier, and the person's response to the anesthetic may be a clue to the diagnosis. Anesthetic eye drops do not relieve pain that is caused by glaucoma, uveitis, or scleritis.
Testing
Testing is usually unnecessary.
If doctors suspect a viral infection (herpes simplex virus or varicella-zoster virus), they may take samples of discharge or blister fluid to send to the laboratory. The sample is placed in a culture medium (a substance that allows bacteria or viruses to grow). Samples for culture may also be taken when the person has a corneal ulcer so doctors can give antibiotics that are most likely to be effective. Gonioscopy (use of a special lens to examine the drainage channels in the eye) is done in people with glaucoma. Sometimes people with uveitis are tested for autoimmune disorders, especially if there is no obvious cause (such as an injury) for the uveitis.
People with scleritis Scleritis Scleritis is severe, destructive inflammation of the sclera (the tough, white, fiber layer covering the eye) that may threaten vision. Scleritis sometimes occurs in people who have a bodywide... read more are usually referred to an ophthalmologist who often does additional tests.
Treatment
The cause is treated. Eye redness itself does not require treatment. It usually clears up on its own as the cause resolves (for example, a few days for infectious conjunctivitis or a couple of weeks for subconjunctival hemorrhage). Cool washcloths or artificial tears can be applied if any itching is particularly bothersome. Eye drops that aim to eliminate redness (available over-the-counter) are not recommended.
Key Points
Usually, eye redness is caused by conjunctivitis.
Pain, a rash around the eye or nose, and changes in vision suggest a potentially serious cause.
