Red Eye: When It Is More Than Conjunctivitis

A red eye is one of the most common eye complaints, but redness itself is not a diagnosis. The eye can become red because of allergy, dryness, infection, inflammation, a surface injury or a problem deeper inside the eye.

Many causes are minor. Some are not.

What matters most is often what accompanies the redness. An itchy eye with watery discharge tells a different story from a deeply painful eye with blurred vision and light sensitivity.

Common Causes of Redness

Allergic eye disease commonly causes prominent itching, watering and swelling, often affecting both eyes. Conjunctivitis may cause redness together with a gritty sensation and discharge.

Dry eye and eyelid inflammation can also create persistent redness, burning and fluctuating discomfort.

A subconjunctival haemorrhage looks dramatic because a small blood vessel has leaked beneath the clear membrane covering the white of the eye. It usually appears as a sharply defined bright-red patch and, when there has been no significant injury and vision is unaffected, is often less serious than it looks.

These conditions can sometimes be distinguished from one another by their accompanying symptoms, but appearance alone is not always enough.

When the Cornea Is Involved

The cornea is the clear, sensitive surface at the front of the eye. An abrasion, infection or ulcer involving the cornea can cause significant pain, watering, blurred vision and sensitivity to light.

Contact lens wear is particularly important. A red, painful eye in someone wearing contact lenses should not simply be assumed to be ordinary conjunctivitis, because contact lens wear increases the risk of microbial keratitis, an infection that can progress quickly and damage the cornea.

Remove the contact lenses and seek prompt assessment rather than putting another pair in and waiting for the redness to settle.

Inflammation Inside the Eye

Uveitis describes inflammation within the eye. Anterior uveitis, sometimes called iritis, often causes a deep ache, redness around the cornea, blurred vision and marked light sensitivity.

Treatment is very different from the treatment of ordinary conjunctivitis and usually requires specialist examination and prescription medication.

Another important cause of a painful red eye is acute angle-closure glaucoma, where eye pressure rises rapidly. Severe pain, blurred vision or coloured halos together with headache, nausea or vomiting requires urgent medical attention.

Why Leftover Eye Drops Can Be a Problem

When an eye becomes red, it is tempting to use whatever eye drops happen to be in the medicine cabinet.

This is particularly risky with steroid-containing drops. Steroids are valuable medicines when used for the correct diagnosis, but they can worsen certain eye infections and may delay the correct treatment of a serious condition.

Antibiotic drops are also not appropriate for every red eye. Viral, allergic and inflammatory eye problems do not become better simply because an antibiotic has been added.

Treatment should match the cause.

When a Red Eye Needs Prompt Assessment

Seek urgent assessment when redness is accompanied by significant pain, reduced or distorted vision, pronounced light sensitivity, a recent eye injury, chemical exposure, severe headache or nausea.

A red eye in a contact lens wearer also deserves particular caution.

Redness without pain or visual change is often less urgent, but persistent or repeatedly recurring symptoms should still be investigated.

Medical information cross-checked against NHS ophthalmic guidance regarding red eye, eye pain and uveitis.