Eye redness (red eye)
Redness of the white of the eye, from dilated surface blood vessels. Most causes are minor — conjunctivitis, allergy, dryness or a harmless burst vessel — but redness with pain, reduced vision or light sensitivity can signal a serious eye problem needing urgent care.
What it means
A red eye is redness of the normally white part of the eye, caused by widening or leaking of the small surface blood vessels. The great majority of causes are minor and self-limiting: conjunctivitis (inflammation of the surface membrane) from a viral or bacterial infection or an allergy, dry eye, mild irritation from smoke, dust or contact lenses, or a subconjunctival haemorrhage — an alarming but harmless bright-red patch from a tiny burst vessel that clears on its own. The key task is to separate these from the smaller number of serious causes, which threaten sight and share particular warning features: significant eye pain, reduced or blurred vision, marked sensitivity to light, or a red eye with a headache and nausea. These can indicate conditions such as iritis (uveitis), a corneal ulcer or scratch, acute glaucoma, or scleritis, all of which need urgent eye assessment. A painless red eye with normal vision, by contrast, is usually not serious.
Common causes
- Conjunctivitis — viral (watery, often both eyes, with a cold), bacterial (sticky discharge), or allergic (itchy, with hay-fever symptoms).
- Dry eye — gritty, tired, intermittently red eyes.
- Subconjunctival haemorrhage — a bright-red painless patch from a burst surface vessel; harmless, clears in days.
- Irritation — smoke, dust, chlorine, contact lens overuse.
- Serious causes (with pain, reduced vision or light sensitivity) — iritis/uveitis, corneal ulcer or scratch, acute glaucoma, scleritis — these need urgent care.
- Sometimes — a red eye is part of an autoimmune condition (e.g. with Sjögren's or inflammatory arthritis).
Lab work-up approach
A red eye is diagnosed by examining the eye, not by blood tests, and most cases need no tests. Blood tests have a limited, supporting role: when a red eye is part of a suspected autoimmune condition (for example recurrent iritis, or dryness suggesting Sjögren's), tests such as ANA, inflammatory markers (CRP, ESR) and specific antibodies may be relevant, arranged alongside an eye assessment. Mediora.AI can surface an autoimmune or inflammatory pattern from your results when the eye problem points that way; the essential step for a red eye — especially a painful one or with reduced vision — is a direct eye examination, not a blood test.
Tests Mediora.AI can interpret
Related conditions
Panels to consider
When to see a doctor
Seek urgent eye assessment (same day) for a red eye with significant pain, reduced or blurred vision, marked sensitivity to light, a red eye after an injury or with a chemical splash, a red eye with a headache and nausea (possible acute glaucoma), or in a contact lens wearer with pain — these can threaten sight. A newborn with a red, discharging eye also needs prompt review. Most other red eyes — itchy allergic eyes, a sticky infective conjunctivitis, or a painless bright-red haemorrhage with normal vision — are minor and settle with simple measures or briefly with your GP or pharmacist. Mediora.AI helps flag an autoimmune contributor when relevant; a painful red eye or one affecting vision needs an eye specialist urgently.