Red Eyes

An eye that suddenly becomes red is one of the main reasons people seek the services of an eye doctor. And for good reason.

Significant discomfort, blurred vision or both often accompany a red eye. And, well, a red eye just looks bad, too.

The front surface of the eye is composed of two structures: the clear cornea in the center of the eye (overlying the colored iris and the pupil), and the tough, opaque sclera–the “white” of the eye that surrounds the cornea and forms the outer coating of most of the eyeball.

An eye becomes red when the tiny blood vessels that lie on top of the sclera (and under a thin, clear membrane called the conjunctiva) become inflamed. It is the blood in these engorged vessels that obscure the underlying white sclera and make the eye appear red.

Without an examination, it can be difficult, if not impossible, to determine the underlying cause of a red eye and whether the condition is an emergency or not.

Causes of Red Eye

There are many conditions that can cause an eye to become red. Here are a few of the most common:


Conjunctivitis, commonly called “pink eye,” can occur at any age and can affect one eye or both eyes. There are three main categories of pink eye, depending on the underlying cause:

  • Viral conjunctivitis. This is the type of conjunctivitis most people are referring to when they say they have pink eye. Caused by a common virus, viral pink eye (like a common cold) typically resolves over several days without treatment and is not associated with serious vision problems.Symptoms of viral conjunctivitis include redness, itching and a watery discharge. Though viral pink eye usually is not serious, it produces significant discomfort and is highly contagious.
  • Bacterial conjunctivitis. This is a less common but more serious type of pink eye, caused by bacteria. Symptoms include redness and a sticky, mucous-like discharge.Bacterial conjunctivitis should be treated promptly with medicated eye drops or ointments, to prevent a serious infection of the eye, which could lead to a corneal ulcer and scarring that could cause permanent vision loss.
  • Allergic conjunctivitis. As its name suggests, this type of pink eye is associated with common allergies. Symptoms are very similar to viral conjunctivitis, but both eyes are affected and the condition is accompanied by other allergy symptoms such as nasal congestion, a runny nose and sneezing.Since allergic conjunctivitis can be a chronic or seasonal problem, ask your eye doctor about medications that can prevent or lessen the severity of future episodes.

Dry eyes

Another common cause of eye redness is dry eyes. Other symptoms of dry eyes include a feeling that something is “in” your eyes (called a foreign body sensation), a scratchy feeling, sensitivity to light and intermittent blurred vision.

Oddly enough, another symptom is watery eyes. Dry eyes cause irritation of the surface of the eye, and this irritation causes the lacrimal glands located above and slightly behind the eyes to over-produce the watery component of normal tears as a reflex mechanism to protect the eyes from dryness-related damage.

Unfortunately, because other components of the normal tear layer (oil and mucous) are not present in these watery “reflex tears,” the dry eye condition persists despite the apparent surplus of tears.

Redness caused by dry eyes usually can be successfully treated with routine use of non-prescription artificial tears or by other treatments your eye doctor can prescribe.

Contact lenses

Contact lens wear is another cause of red eyes in some individuals. In particular, a condition called contact lens acute red eye (CLARE) is associated with contact lens wear and causes a fast onset of redness, eye pain, sensitivity to light and watery eyes.

CLARE appears to be an inflammatory condition caused by endotoxins produced by certain types of bacteria that can accumulate on contact lenses and in contact lens storage cases. The condition usually resolves within a few days after contact lens wear is discontinued. Your eye doctor might also prescribe anti-inflammatory eye drops to help clear the redness.

Corneal infections

Infections of the cornea (also called infectious keratitis) are a serious cause of red eyes that usually require prompt treatment to avoid corneal ulcers, scarring and vision loss. Most corneal infections are accompanied by eye pain, sensitivity to light and watery eyes. Blurred vision also can occur.

The cause of the infection–bacteria, fungus or other microorganisms–determines the proper treatment for infections keratitis. Treatment usually consists of frequent use of medicated eye drops and/or ointments.


Episcleritis is inflammation located between the sclera and overlying conjunctiva. It usually causes a pink or purple color to the sclera and sensitivity to light and watery eyes.

The cause of episcleritis usually is unknown, but it sometimes is associated with an underlying systemic condition, such as rheumatoid arthritis. The condition usually disappears without treatment within a week or two, but your eye doctor might prescribe corticosteroid eye drops to relieve symptoms faster.


Scleritis is inflammation of the sclera itself. Symptoms are similar to those of episcleritis, but typically are more severe.

Inflammation of the sclera usually is associated with autoimmune diseases such as rheumatoid arthritis and lupus, but sometimes the cause is unknown.

Corticosteroid eye drops commonly are prescribed to treat scleritis. Oral medicines sometimes are used as well. If your eye doctor suspects an underlying disease is involved, he or she might refer you to a physician for a physical exam and blood tests to rule out systemic diseases.

Acute glaucoma

A condition called acute angle closure glaucoma can cause an abrupt red eye accompanied by pain, blurred vision, nausea and vomiting. This type of glaucoma is a medical emergency and requires immediate treatment to prevent or limit permanent vision loss.

Don’t Take Chances

The only way to determine the cause and proper treatment of a red eye is to see your eye doctor for an evaluation.

Don’t take chances with your eyes by waiting to see if a red eye will get better on its own. Call your eye doctor immediately to see if urgent care is required.

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