Eye Redness: What Causes Red Eyes

Why eyes turn red

The white of the eye (sclera) is covered by a thin, clear membrane called the conjunctiva. It contains tiny blood vessels that are normally almost invisible. When the eye is irritated or inflamed, these vessels widen and the eye looks pink or bloodshot. This is called ocular hyperemia.

The pattern of redness tells a doctor where the problem is:

• Diffuse redness, strongest toward the corners: the conjunctiva, as in conjunctivitis or dry eye.
• A red ring around the colored part of the eye (ciliary flush): inflammation inside the eye or of the cornea, as in uveitis, keratitis or glaucoma.
• A solid, bright red patch: blood under the conjunctiva.
• Deep, purplish redness with boring pain: scleritis.

Types of eye redness and their causes

Conjunctivitis (pink eye)

Conjunctivitis is the most common cause of a red eye.

Vision is normal and pain is mild in all three.

Dry eye

Dry eye causes mild redness, burning, a gritty or sandy feeling, and paradoxically watery eyes. It worsens with screen use, air conditioning, wind and as the day goes on. It is common after age 50, in women after menopause, and with some medicines.

Blepharitis

Blepharitis is inflammation of the eyelid margins. Eyelids look red and crusty, especially in the morning, with flakes on the lashes. It often comes with dry eye and styes.

Subconjunctival hemorrhage

A subconjunctival hemorrhage is a broken blood vessel under the conjunctiva. It looks alarming, a bright red patch, but it is painless, does not affect vision and fades over 1 to 2 weeks. Coughing, sneezing, straining, rubbing the eye and blood thinners make it more likely. Repeated episodes should prompt a blood pressure check.

Irritants and contact lenses

Smoke, chlorine, cosmetics, a speck of dust and lack of sleep can all redden the eyes. Contact lens overwear causes redness from reduced oxygen to the cornea. A contact lens wearer with a painful red eye needs urgent review to rule out infection.

Serious causes

• Acute angle-closure glaucoma: a sudden rise in eye pressure. Severe eye pain, headache, blurred vision, haloes around lights, a mid-sized pupil that does not react, and nausea or vomiting. It can cause permanent vision loss within hours.
• Uveitis or iritis: inflammation inside the eye. Aching pain, redness around the cornea, light sensitivity and a small pupil. It is linked with ankylosing spondylitis, inflammatory bowel disease and psoriasis.
• Keratitis and corneal ulcer: infection or inflammation of the cornea. Pain, light sensitivity, blurred vision and sometimes a white spot. Contact lenses, injury and herpes are common causes.
• Scleritis: deep, severe, boring pain that may wake you at night, with a dark red or purple tinge. Often linked to rheumatoid arthritis.
• Injury: scratches, foreign bodies and chemical burns.

Harmless or serious: how to tell

How a red eye is diagnosed

A doctor or optometrist will ask about pain, vision, discharge, itch, contact lens use, injury and other conditions. They will:

1. check vision with an eye chart
2. look at the pattern of redness, the pupils and the eyelids
3. use fluorescein, an orange dye, with a blue light to show scratches or ulcers on the cornea
4. use a slit lamp microscope to look for inflammatory cells inside the eye
5. measure eye pressure if glaucoma is possible

A swab is taken only for severe or unusual conjunctivitis, newborns, or suspected corneal infection.

Treatment and home care

Self-care for mild red eyes

• Artificial tears (preservative-free if used more than 4 times a day) for dry eye and irritation.
• Cool compresses for itch and swelling.
• Antihistamine eye drops from a pharmacy for allergic redness.
• Warm compresses and eyelid cleaning for blepharitis.
• Stop wearing contact lenses until the eye is completely normal.
• Wash your hands often and avoid sharing towels if conjunctivitis is possible.

Avoid using "redness relief" drops that contain decongestants such as tetrahydrozoline for more than a few days. They shrink the vessels briefly, but rebound redness follows.

Treatment from a doctor

• Antibiotic drops or ointment for bacterial conjunctivitis or corneal infection.
• Antiviral treatment for herpes eye infections.
• Steroid drops for uveitis, prescribed only by an eye specialist, because steroids can make some infections much worse.
• Emergency pressure-lowering treatment and laser for acute glaucoma.

Frequently asked questions

What causes eye redness?

The most common causes are conjunctivitis (viral, bacterial or allergic), dry eye, blepharitis, a broken blood vessel, tiredness and irritants like smoke or contact lenses. Less often, redness comes from glaucoma, inflammation inside the eye or an infected cornea, which cause pain and blurred vision.

What eye diseases cause redness?

Conjunctivitis, dry eye disease, blepharitis, subconjunctival hemorrhage, uveitis (iritis), keratitis, corneal ulcers, acute angle-closure glaucoma, scleritis and episcleritis all cause red eyes. The serious ones usually also cause pain, light sensitivity or reduced vision.

When should I worry about a red eye?

See a doctor the same day if the red eye is painful, light-sensitive, has blurred vision, follows an injury or chemical splash, or occurs in a contact lens wearer. Go to the ER for sudden severe pain with haloes, headache and vomiting.

Is a bright red spot on the white of my eye dangerous?

Usually not. A painless, flat, bright red patch is most often a subconjunctival hemorrhage, a small broken blood vessel. It clears in 1 to 2 weeks without treatment. See a doctor if it follows an injury, keeps happening, or you take blood thinners.

Why are my eyes red when I wake up?

Morning redness is often from dry eye, especially if you sleep with a fan or your eyelids do not close fully, from blepharitis, from sleeping in contact lenses, or from alcohol or poor sleep the night before. Allergies to dust mites can also cause it.