Author: Dr Val Phua
Estimated reading time: 14–16 minutes
What Is a Red Eye?
A red eye occurs when blood vessels on or around the surface of the eye become enlarged, inflamed or damaged.
The redness may appear as:
- Fine visible blood vessels
- General pinkness over the white of the eye
- Intense redness around the cornea
- A localised bright-red patch
- Deep bluish-red or purple discolouration
- Redness with swollen conjunctiva
- Redness affecting the eyelids and surrounding skin
Red eye is a symptom rather than a diagnosis.
Common causes include:
- Dry eye
- Blepharitis
- Allergy
- Viral conjunctivitis
- Bacterial conjunctivitis
- A broken surface blood vessel
- Contact-lens irritation
More serious causes include:
- Corneal infection
- Uveitis
- Scleritis
- Acute angle-closure glaucoma
- Chemical injury
- Eye trauma
- Infection after eye surgery or injection
- Orbital cellulitis
The appearance alone does not always reveal whether the cause is harmless. Pain, light sensitivity, reduced vision, contact-lens use, trauma and recent surgery are often more important than how red the eye looks.
Why Does the Eye Become Red?
The white part of the eye is called the sclera.
It is covered by a transparent membrane called the conjunctiva, which contains many small blood vessels.
When the eye is irritated or inflamed, these vessels may:
- Widen
- Become more visible
- Leak fluid
- Bleed
- Be joined by deeper inflamed vessels
Redness may arise from several layers:
- Conjunctiva
- Episclera
- Sclera
- Cornea
- Iris and ciliary body
- Eyelids
- Orbit
The pattern and depth of redness can help the clinician identify which tissues are involved.
Is Every Red Eye Conjunctivitis?
No.
Conjunctivitis is common, but several other conditions can look similar.
A red eye may result from:
- Dry eye
- Allergy
- Corneal abrasion
- Contact-lens-related keratitis
- Uveitis
- Episcleritis
- Scleritis
- Acute glaucoma
- Trauma
- Chemical exposure
- Herpes infection
- Eyelid or orbital infection
Conjunctivitis usually causes irritation, watering, itching or discharge. Severe pain, marked photophobia or true visual reduction should raise concern for a condition involving the cornea, internal eye, sclera or orbit.
What Details Help Determine the Cause?
Important questions include:
- Did the redness begin suddenly or gradually?
- Is one eye affected or both?
- Is the eye painful?
- Is there itching?
- Is there discharge?
- Is vision blurred or reduced?
- Is the eye sensitive to light?
- Is a contact lens being worn?
- Has there been trauma or chemical exposure?
- Was there recent eye surgery, laser or injection?
- Are the eyelids swollen?
- Is there fever?
- Does moving the eye hurt?
- Is there a rash or blisters around the forehead or nose?
- Are there headache, nausea or halos around lights?
These details help separate surface irritation from potentially urgent disease.
When Is a Red Eye an Emergency?
Seek immediate or same-day eye care for a red eye accompanied by:
- Moderate or severe pain
- Reduced or lost vision
- Marked sensitivity to light
- A cloudy cornea
- A white or grey spot on the cornea
- Severe headache
- Halos around lights
- Nausea or vomiting
- An abnormal or irregular pupil
- Contact-lens wear with pain or blur
- Chemical exposure
- Penetrating or high-speed trauma
- Recent eye surgery or injection
- Significant eyelid swelling with fever
- Pain or restriction when moving the eye
- A bulging eye
- Double vision
- A forehead or eyelid blistering rash
Pain, photophobia and changes in vision are recognised red flags in a red eye and should not be managed as routine conjunctivitis without examination.
Can a Serious Red Eye Be Painless?
Yes.
Some important conditions may cause little pain, including:
- Early corneal infection in a patient with reduced corneal sensation
- Neurotrophic keratopathy
- A postoperative wound leak
- Certain forms of uveitis
- Subconjunctival haemorrhage
- Some retinal or optic-nerve diseases occurring alongside surface redness
A painless red eye with normal vision is generally less concerning than a painful red eye with visual loss, but it should still be assessed when the redness is unexplained, recurrent or persistent.
Common Patterns of Redness
Diffuse Pink or Red Conjunctiva
May occur with:
- Viral conjunctivitis
- Bacterial conjunctivitis
- Allergy
- Dry eye
- Medication toxicity
- Environmental irritation
Redness Concentrated Around the Cornea
Sometimes called ciliary or circumcorneal injection.
It may suggest:
- Uveitis
- Keratitis
- Acute angle closure
- Significant corneal inflammation
Localised Bright-Red Patch
More suggestive of:
- Subconjunctival haemorrhage
- Local trauma
- A small conjunctival lesion
Deep Bluish-Red or Purple Redness
May occur with:
- Scleritis
- Severe deep inflammation
Redness with Marked Swelling
May occur with:
- Allergy
- Severe conjunctivitis
- Chemical injury
- Orbital or preseptal cellulitis
- Thyroid eye disease
These visual patterns are helpful but are not sufficiently reliable for self-diagnosis.
One Red Eye Versus Two Red Eyes
One Red Eye
More concerning causes include:
- Corneal abrasion
- Foreign body
- Keratitis
- Uveitis
- Episcleritis
- Scleritis
- Acute angle closure
- Trauma
- Herpes eye disease
- Orbital infection
Conjunctivitis may begin in one eye and later spread to the other.
Two Red Eyes
Common causes include:
- Viral conjunctivitis
- Allergy
- Dry eye
- Blepharitis
- Environmental irritation
- Medication toxicity
- Systemic inflammatory disease
Bilateral redness does not automatically mean the condition is harmless.
Itching, Pain, Discharge or Photophobia?
Prominent Itching
More suggestive of:
- Allergic conjunctivitis
- Eyelid allergy
- Contact dermatitis
Burning or Grittiness
More suggestive of:
- Dry eye
- Blepharitis
- Viral conjunctivitis
- Environmental irritation
Sticky or Purulent Discharge
May suggest:
- Bacterial conjunctivitis
- Severe infection
- Eyelid infection
Watery Discharge
May occur with:
- Viral conjunctivitis
- Allergy
- Dry eye
- Corneal irritation
Significant Pain
Raises concern for:
- Corneal abrasion
- Keratitis
- Uveitis
- Scleritis
- Acute angle closure
- Trauma
- Postoperative infection
Marked Photophobia
Raises concern for:
- Corneal disease
- Uveitis
- Severe ocular-surface inflammation
- Postoperative inflammation
No single symptom is perfectly diagnostic, but severe pain, photophobia and reduced vision should shift the assessment away from routine conjunctivitis.
Dry Eye Disease
Dry eye is a common cause of mild redness.
Associated symptoms may include:
- Burning
- Stinging
- Grittiness
- Watering
- Tired eyes
- Fluctuating blur
- Discomfort during screen use
- Symptoms in air conditioning or wind
The redness is often:
- Mild or moderate
- Present in both eyes
- Variable through the day
- Improved temporarily by blinking or lubrication
Persistent one-sided redness, significant pain, photophobia or reduced vision should not be attributed to dry eye without examination.
Blepharitis and Meibomian Gland Dysfunction
Blepharitis is inflammation of the eyelid margins.
It may cause:
- Red eyelid edges
- Crusting around the eyelashes
- Burning
- Grittiness
- Watering
- Recurrent styes
- Unstable tears
- Mild conjunctival redness
Meibomian gland dysfunction reduces the quality of the oily tear layer, allowing tears to evaporate more quickly.
Treatment may include:
- Warm compresses
- Eyelid hygiene
- Artificial tears
- Treatment of rosacea or Demodex
- Prescription medication in selected patients
Allergic Conjunctivitis
Allergic conjunctivitis occurs when the ocular surface reacts to an allergen.
Possible triggers include:
- Dust mites
- Pollen
- Animal dander
- Mould
- Cosmetics
- Eye drops
- Contact-lens solutions
Typical symptoms include:
- Intense itching
- Watering
- Redness
- Puffy eyelids
- Stringy mucus
- Symptoms affecting both eyes
- Associated sneezing or nasal allergy
Itching is one of the strongest clues favouring allergy.
Treatment may include:
- Avoiding the allergen
- Cool compresses
- Preservative-free lubricants
- Antihistamine or mast-cell-stabilising eye drops
- Treatment of associated eyelid inflammation
Singapore HealthHub lists red, itchy, watery eyes and eyelid swelling among typical allergic-conjunctivitis symptoms.
Can Eye Allergy Be Painful?
Mild burning or irritation can occur.
Severe pain, substantial photophobia or reduced vision is not typical and requires assessment for:
- Keratitis
- Uveitis
- Acute glaucoma
- Corneal abrasion
- Another diagnosis
Viral Conjunctivitis
Viral conjunctivitis commonly causes:
- Watery redness
- Grittiness
- Burning
- Swollen eyelids
- Light discharge
- Tender lymph nodes near the ear
- Recent cold, sore throat or respiratory infection
It often begins in one eye before spreading to the other.
Some viruses produce more severe inflammation, including:
- Corneal involvement
- Significant photophobia
- Blurred vision
- Pseudomembranes
- Prolonged corneal spots or haze
Viral conjunctivitis is often highly contagious and may spread through hands, towels, eye secretions and contaminated surfaces. HealthHub identifies conjunctivitis as the most common eye infection and notes that viral, bacterial and allergic causes are possible.
How Long Does Viral Conjunctivitis Last?
Mild cases may improve within one to two weeks.
More severe adenoviral disease may last several weeks, and corneal involvement may affect visual quality for longer.
The condition should be reviewed when:
- Vision becomes reduced
- Pain or photophobia increases
- Thick membranes develop
- The cornea becomes cloudy
- Symptoms are not improving
- The patient is immunocompromised
- Only one eye remains persistently affected
Is Antibiotic Treatment Needed for Viral Conjunctivitis?
Antibiotics do not kill viruses.
They may occasionally be prescribed when:
- Bacterial infection cannot be excluded
- There is a secondary bacterial concern
- The clinical situation is unusual
- The patient has other risk factors
Routine unnecessary antibiotic use may cause:
- Allergy
- Surface toxicity
- Resistance
- False reassurance
Can Steroid Drops Treat Viral Conjunctivitis?
Steroids may occasionally be used by an ophthalmologist for severe inflammation, membranes or visually significant corneal involvement.
They should not be self-started because steroids can:
- Worsen herpes infection
- Prolong some viral infections
- Raise eye pressure
- Cause cataract with prolonged use
- Mask worsening disease
Bacterial Conjunctivitis
Bacterial conjunctivitis may cause:
- Redness
- Yellow or green discharge
- Eyelids stuck together on waking
- Crusting
- Grittiness
- Mild burning
It may affect one or both eyes.
Treatment depends on:
- Severity
- Age
- Contact-lens use
- Immune status
- Corneal involvement
- Likely organism
A red eye with significant pain, photophobia or reduced vision should not be treated as simple bacterial conjunctivitis without examining the cornea.
What Does the Type of Discharge Mean?
Watery Discharge
More commonly associated with:
- Viral conjunctivitis
- Allergy
- Dry eye
- Corneal irritation
Stringy or Ropy Mucus
More commonly associated with:
- Allergy
- Severe dry eye
Thick Yellow or Green Discharge
May occur with:
- Bacterial conjunctivitis
- Eyelid infection
- More aggressive bacterial disease
Copious Purulent Discharge
May suggest a severe bacterial infection requiring urgent assessment and microbiological testing.
Discharge appearance helps guide the diagnosis but is not definitive.
How Can Conjunctivitis Be Prevented from Spreading?
Helpful measures include:
- Wash hands frequently.
- Avoid touching or rubbing the eyes.
- Do not share towels, pillows or cosmetics.
- Clean discharge using fresh disposable material.
- Do not share eye drops.
- Discard contaminated eye makeup.
- Avoid swimming while the eyes remain actively infected.
- Follow workplace, school or healthcare infection-control advice.
A drop bottle used in an infected eye should not be shared with another person.
Can I Go to Work or School with Conjunctivitis?
This depends on:
- Severity
- Cause
- Local policy
- Occupation
- Ability to maintain hygiene
- Whether the person works in healthcare, food preparation or childcare
Conjunctivitis spreads most easily when there is active discharge and frequent hand-to-eye contact.
Subconjunctival Haemorrhage
A subconjunctival haemorrhage occurs when a small blood vessel breaks beneath the transparent conjunctiva.
It commonly appears as:
- A sharply defined bright-red patch
- Blood covering part of the white of the eye
- A dramatic-looking area without general inflammation
It is usually:
- Painless
- Not associated with discharge
- Not associated with photophobia
- Not associated with visual loss
Possible triggers include:
- Coughing
- Sneezing
- Vomiting
- Straining
- Heavy lifting
- Eye rubbing
- Minor trauma
- High blood pressure
- Blood-thinning medication
The blood usually fades like a bruise, changing colour before disappearing over approximately one to two weeks.
When Should a Subconjunctival Haemorrhage Be Assessed?
Arrange assessment when:
- There was significant trauma.
- The eye is painful.
- Vision is affected.
- Blood appears inside the coloured or central part of the eye.
- Haemorrhages occur repeatedly.
- There is unexplained bruising or bleeding elsewhere.
- The patient uses anticoagulants.
- Blood pressure has not been checked.
- Both eyes are affected without a clear cause.
- The redness does not resolve as expected.
Do not stop prescribed blood-thinning medication independently.
Episcleritis
Episcleritis is inflammation of a superficial tissue layer between the conjunctiva and sclera.
It commonly causes:
- A localised red patch
- Mild irritation
- Mild tenderness
- Watering
- Little or no visual change
It is usually less painful and less dangerous than scleritis.
Some cases occur without an identifiable cause. Recurrent episodes may occasionally be associated with systemic inflammatory disease.
Scleritis
Scleritis is inflammation of the deeper white wall of the eye.
It may cause:
- Severe deep pain
- Throbbing or boring discomfort
- Pain radiating to the brow, temple, jaw or face
- Pain waking the patient at night
- Pain worsened by eye movement
- Deep red, bluish-red or purple discolouration
- Tenderness
- Reduced vision in severe disease
Scleritis may involve the cornea or internal eye and can threaten sight.
It may be associated with systemic autoimmune or inflammatory disease, including rheumatoid arthritis and vasculitis. The AAO describes scleritis as a painful inflammation of the sclera and surrounding tissues that may require investigation for an underlying systemic disorder.
How Is Episcleritis Different from Scleritis?
Episcleritis
- Usually mild discomfort
- Often localised redness
- Vision generally normal
- Usually self-limiting
- Less commonly associated with serious systemic disease
Scleritis
- Deep, often severe pain
- May wake the patient from sleep
- May be tender to touch
- Deeper bluish-red appearance
- May reduce vision
- May threaten the integrity of the eye
- More strongly associated with systemic inflammatory disease
Clinical examination is needed because the distinction may not be obvious from a photograph.
Corneal Abrasion
A corneal abrasion is a scratch on the clear front surface of the eye.
Possible causes include:
- Fingernails
- Paper
- Plant material
- Dust or grit
- Makeup tools
- Contact-lens injury
- Rubbing
Symptoms may include:
- Sudden sharp pain
- Watering
- Redness
- Foreign-body sensation
- Photophobia
- Blurred vision
- Difficulty opening the eye
Fluorescein dye and slit-lamp examination help identify the abrasion.
Retained Foreign Body
A foreign body may be located:
- On the cornea
- Under the upper eyelid
- In the conjunctiva
- Inside the eye after a penetrating injury
Pain with every blink may occur when a particle beneath the upper eyelid repeatedly scratches the cornea.
Do not attempt to remove:
- An embedded object
- Metal lodged in the cornea
- Glass
- An object protruding from the eye
- Any object following high-speed power-tool injury
Keratitis and Corneal Ulcer
Keratitis is inflammation or infection of the cornea.
A corneal ulcer is an area of epithelial loss with underlying corneal inflammation or infection.
Symptoms may include:
- Pain
- Redness
- Photophobia
- Blurred or reduced vision
- Watering
- Discharge
- A white or grey corneal spot
- Difficulty keeping the eye open
Possible causes include:
- Bacteria
- Fungi
- Herpes viruses
- Acanthamoeba
- Trauma
- Contact-lens wear
- Severe dry eye
- Eyelid exposure
Corneal infection can progress rapidly and result in scarring, perforation or permanent visual loss.
Why Is a White Spot on the Cornea Important?
A visible white, cream or grey spot may represent:
- A corneal infiltrate
- An ulcer
- Infection
- Scar tissue
- A retained foreign body
A new white corneal spot with redness, pain or photophobia requires urgent assessment.
Red Eye in a Contact-Lens Wearer
A contact-lens wearer with a red eye should remove the lens immediately.
Urgent assessment is needed when there is:
- Pain
- Photophobia
- Sudden blur
- Discharge
- Excessive watering
- A white corneal spot
- Symptoms that persist after lens removal
Contact-lens-related microbial keratitis may be bacterial, fungal, viral or Acanthamoeba-related and can threaten sight.
The CDC advises contact-lens wearers with redness, worsening pain, light sensitivity, sudden blur, watering or discharge to remove their lenses and contact an eye doctor immediately.
Contact-Lens Behaviours That Increase Infection Risk
Risk increases with:
- Sleeping or napping in lenses
- Swimming in lenses
- Showering in lenses
- Rinsing lenses or cases with tap water
- Reusing old solution
- Topping up solution
- Wearing lenses longer than recommended
- Poor hand hygiene
- Using damaged lenses
- Using an old or dirty lens case
Sleeping in lenses substantially increases the risk of contact-lens-related eye infection, even when the lenses have been marketed for extended wear.
Acanthamoeba Keratitis
Acanthamoeba keratitis is an uncommon but serious corneal infection.
It is associated particularly with:
- Water exposure while wearing contact lenses
- Tap-water contact
- Swimming or showering in lenses
- Poor disinfection
- Homemade saline
- Contaminated lens cases
Symptoms may include:
- Persistent pain
- Redness
- Blurred vision
- Photophobia
- Watering
- Foreign-body sensation
The condition can resemble other infections and may require prolonged treatment.
Herpes Simplex Eye Infection
Herpes simplex virus may affect the:
- Eyelids
- Conjunctiva
- Corneal epithelium
- Deeper cornea
- Iris
Symptoms may include:
- Redness
- Pain
- Watering
- Photophobia
- Blurred vision
- Recurrent one-sided episodes
Herpes keratitis may scar the cornea and cause permanent visual loss.
Steroid drops can worsen active epithelial herpes if used without appropriate antiviral treatment and ophthalmic supervision.
Shingles Around the Eye
Herpes zoster ophthalmicus occurs when shingles affects the nerve supplying the forehead and eye.
Possible features include:
- Pain or burning on one side of the forehead
- Blisters on the forehead or upper eyelid
- Red eye
- Photophobia
- Blurred vision
- Keratitis
- Uveitis
- Raised eye pressure
A rash near the eye—especially involving the tip or side of the nose—requires prompt medical and ophthalmic assessment.
Shingles involving the eye may cause recurrent keratitis, iritis, glaucoma, scarring and visual loss.
Uveitis
Uveitis is inflammation inside the eye.
Anterior uveitis, also called iritis, commonly causes:
- Deep aching pain
- Redness concentrated near the cornea
- Photophobia
- Blurred vision
- Watering
- Floaters
- A small or irregular pupil
It may affect one or both eyes.
Possible causes include:
- Autoimmune disease
- Infection
- Trauma
- Previous surgery
- No identifiable cause
Uveitis requires prompt treatment because complications may include:
- Cataract
- Glaucoma
- Macular oedema
- Scar tissue
- Permanent visual loss
Uveitis commonly presents with pain, red or watery eyes, blurred vision and light sensitivity.
Acute Angle-Closure Glaucoma
Acute angle closure occurs when the eye’s drainage angle becomes suddenly blocked.
Eye pressure rises rapidly.
Symptoms may include:
- Severe eye or brow pain
- Marked redness
- Misty or blurred vision
- Rainbow halos
- Headache
- Nausea
- Vomiting
- A cloudy cornea
- A mid-sized or poorly reactive pupil
This is an emergency because sustained high pressure may permanently damage the optic nerve.
Singapore HealthHub advises urgent review for a painful red eye with blurred vision.
Does Chronic Glaucoma Cause a Red Eye?
Primary open-angle glaucoma and normal-tension glaucoma are generally:
- Painless
- Not visibly red
- Gradual
- Initially symptomless
A red eye in a patient with glaucoma may instead result from:
- Dry eye
- Allergy to glaucoma medication
- Preservative toxicity
- Acute angle closure
- Uveitis
- Corneal disease
- A surgical complication
Eye-Drop Allergy or Toxicity
Eye medications may cause redness through:
- Allergy to the active ingredient
- Preservative sensitivity
- Surface toxicity
- Chronic inflammation
- Incorrect or excessive use
Possible symptoms include:
- Redness
- Itching
- Puffy eyelids
- Burning
- Follicles under the eyelids
- Dryness
- Skin irritation
Common examples include:
- Brimonidine allergy
- Preserved glaucoma drops
- Frequent antibiotic use
- Cosmetic redness-relief drops
Do not stop essential glaucoma medication without an alternative pressure-control plan.
Redness-Relief Drops
Drops that constrict surface blood vessels may temporarily make the eye look whiter.
They do not treat the underlying cause.
Frequent use may produce:
- Rebound redness
- Surface irritation
- Masking of serious disease
- Dependence on repeated use
A persistently red eye should be diagnosed rather than cosmetically whitened.
Chemical Eye Injury
Chemical exposure is an emergency.
Potentially harmful substances include:
- Bleach
- Oven cleaner
- Drain cleaner
- Cement
- Lime
- Ammonia
- Laboratory chemicals
- Industrial solvents
- Cleaning products
- Agricultural chemicals
The most important immediate treatment is irrigation.
What to Do Immediately
- Start rinsing the eye at once.
- Use clean tap water or saline.
- Hold the eyelids open.
- Remove contact lenses if they come out easily.
- Continue copious irrigation.
- Arrange emergency medical care.
- Bring the chemical container or safety information when possible.
Do not delay flushing while searching for a special solution.
Strong chemical exposure requires immediate irrigation and emergency assessment.
What Should Not Be Put into a Chemically Injured Eye?
Do not use:
- Vinegar
- Baking soda
- Another chemical intended to neutralise the first
- Redness-relief drops
- Household fluids
- Unprescribed medication
Use water or saline and obtain emergency care.
Eye Trauma
Trauma may cause redness from:
- Conjunctival injury
- Corneal abrasion
- Subconjunctival haemorrhage
- Inflammation inside the eye
- Bleeding into the anterior chamber
- Lens injury
- Raised pressure
- Retinal injury
- Open-globe injury
Seek emergency care for:
- Penetrating injury
- High-velocity impact
- Reduced vision
- Severe pain
- An irregular pupil
- Blood visible inside the eye
- Double vision
- Nausea after trauma
- Fluid leaking from the eye
- An object protruding from the eye
Do not press on an eye when penetration is suspected.
Hyphema
A hyphema is blood within the front chamber of the eye, usually after trauma.
It may cause:
- Pain
- Photophobia
- Blurred or blocked vision
- Visible blood behind the cornea
- Raised eye pressure
Hyphema requires urgent assessment because complications include rebleeding, pressure elevation and corneal staining.
Red Eye After Eye Surgery
Some mild redness is expected after certain procedures.
Urgent warning signs include:
- Increasing pain
- Worsening rather than improving redness
- Reduced vision
- Marked photophobia
- Discharge
- Eyelid swelling
- Nausea or vomiting
- A cloudy cornea
- New floaters or a curtain
- Fluid leaking from the wound
Postoperative infection inside the eye can progress rapidly.
Red Eye After an Intravitreal Injection
A localised subconjunctival haemorrhage may occur where the needle entered and is often harmless.
Mild irritation from antiseptic can also occur.
Urgent assessment is needed for:
- Increasing pain
- Worsening redness
- Reduced vision
- Marked light sensitivity
- Discharge
- Symptoms worsening after initial improvement
A painful red eye with deteriorating vision after an injection may indicate endophthalmitis and requires immediate contact with the treating clinic.
Red Eye After Glaucoma Surgery
A patient with a filtering bleb should seek urgent care for:
- Redness
- Pain
- Photophobia
- Discharge
- Sudden blur
- A white or yellow bleb
- Reduced vision
Bleb infection may occur months or years after trabeculectomy and can spread into the eye.
A visible exposed glaucoma tube also requires prompt assessment.
Preseptal Cellulitis
Preseptal cellulitis is an infection of the eyelid and tissues in front of the orbital septum.
It may cause:
- One-sided eyelid redness
- Swelling
- Tenderness
- Warm skin
- Difficulty opening the eye
- Fever
Vision and eye movements are usually preserved.
The patient still requires medical assessment and antibiotic treatment.
Orbital Cellulitis
Orbital cellulitis is infection involving tissues behind the orbital septum.
It is a serious emergency.
Warning features include:
- Fever
- Severe or worsening eyelid swelling
- Pain with eye movement
- Restricted eye movement
- Double vision
- Reduced vision
- A bulging eye
- Severe headache
- General illness
- Confusion
Orbital cellulitis may threaten sight and spread towards the brain. It usually requires urgent imaging, intravenous antibiotics and specialist care.
Thyroid Eye Disease
Thyroid eye disease may cause:
- Red or gritty eyes
- Puffy eyelids
- Eyelid retraction
- Incomplete closure
- Bulging eyes
- Pain or pressure
- Photophobia
- Double vision
- Restricted eye movement
Rarely, swollen orbital tissues compress the optic nerve.
Urgent assessment is required for:
- Reduced vision
- Faded colour vision
- New field loss
- Severe exposure
- Inability to close the eye
- Rapidly worsening double vision
The NEI lists redness, irritation, puffy eyelids, bulging eyes, pain, pressure and movement difficulty among common features.
Can Lack of Sleep Cause Red Eyes?
Poor sleep may worsen:
- Dry eye
- Tear-film instability
- Eye rubbing
- Contact-lens intolerance
- Eyelid inflammation
Lack of sleep does not adequately explain:
- Severe pain
- Photophobia
- Reduced vision
- A cloudy cornea
- A unilateral persistent red eye
Can Screens Cause Red Eyes?
Long periods of screen use reduce blinking and may aggravate:
- Dry eye
- Burning
- Grittiness
- Fluctuating blur
- Mild redness
Screens do not usually cause a painful, severely red eye or corneal infection by themselves.
Can Swimming Cause a Red Eye?
Possible causes include:
- Chlorine irritation
- Dry eye
- Allergy
- Contact-lens-related infection
- Acanthamoeba exposure
- Viral conjunctivitis
- Corneal abrasion
Contact lenses should not be exposed to swimming-pool, sea, lake, shower or tap water.
Pain, photophobia or blur after swimming requires prompt assessment, particularly in a contact-lens wearer.
Can Smoke or Haze Cause Red Eyes?
Smoke, haze and airborne irritants may cause:
- Burning
- Watering
- Dryness
- Mild redness
- Worsening allergy
Move away from the irritant, avoid rubbing and consider preservative-free lubrication.
Persistent one-sided redness, pain or visual change requires examination.
Can High Blood Pressure Cause a Red Eye?
High blood pressure may be associated with subconjunctival haemorrhage, although many haemorrhages occur without an identifiable cause.
High blood pressure does not usually cause diffuse painful conjunctival redness.
A blood-pressure check may be appropriate for recurrent or unexplained haemorrhage.
Can Blood Thinners Cause a Red Eye?
Anticoagulant or antiplatelet medication may make subconjunctival bleeding:
- More extensive
- More noticeable
- More likely to recur
The medication should not be stopped independently.
Seek medical advice when:
- The bleeding is recurrent
- There is bruising elsewhere
- There was significant trauma
- Vision is affected
- Blood is visible inside the eye
Red Eye in Babies and Children
Children may develop redness from:
- Viral conjunctivitis
- Bacterial conjunctivitis
- Allergy
- Foreign bodies
- Corneal abrasion
- Eyelid infection
- Trauma
- Uveitis
- Orbital cellulitis
Young children may not describe pain or visual loss clearly.
Warning behaviours include:
- Refusal to open one eye
- Avoidance of light
- Persistent crying
- Repeated eye rubbing
- New squint
- Reduced visual attention
- Marked eyelid swelling
- Fever
- A cloudy cornea
- A white pupil
Red or Sticky Eye in a Newborn
A newborn with redness and significant discharge requires prompt medical assessment.
Possible causes include:
- Blocked tear duct
- Bacterial infection
- Viral infection
- Birth-related infection
- Corneal disease
Some neonatal infections can progress rapidly and should not be managed with another family member’s eye drops.
How Is a Red Eye Examined?
History
The clinician asks about:
- Onset
- One or both eyes
- Pain
- Photophobia
- Vision change
- Discharge
- Itching
- Contact lenses
- Trauma
- Surgery
- Medication
- Autoimmune disease
- Infection exposure
- Rash
- Fever
- Headache or nausea
Visual-Acuity Testing
Each eye is tested separately.
Reduced visual acuity is an important red flag and may indicate:
- Corneal disease
- Uveitis
- Acute glaucoma
- Optic-nerve disease
- Postoperative infection
- Orbital disease
Pupil Examination
The pupils are assessed for:
- Size
- Shape
- Symmetry
- Light reaction
- A relative afferent pupillary defect
An abnormal pupil may occur with:
- Acute angle closure
- Uveitis
- Trauma
- Optic-nerve disease
- Neurological disease
Eye-Movement Examination
The clinician checks for:
- Painful movement
- Restricted movement
- Double vision
- Proptosis
These findings are important when orbital disease is suspected.
Slit-Lamp Examination
The slit lamp allows detailed examination of:
- Eyelids
- Conjunctiva
- Cornea
- Anterior chamber
- Iris
- Lens
- Anterior vitreous
It helps distinguish:
- Conjunctivitis
- Keratitis
- Uveitis
- Scleritis
- Foreign body
- Postoperative complications
Fluorescein Staining
Fluorescein dye highlights areas where the corneal surface is damaged.
It may reveal:
- Abrasion
- Ulcer
- Contact-lens injury
- Herpetic patterns
- Dry-eye staining
- Surgical wound leakage
Eyelid Eversion
Turning the upper eyelid helps identify:
- Foreign bodies
- Contact-lens fragments
- Papillae
- Follicles
- Membranes
- Eyelid inflammation
Eye-Pressure Measurement
Tonometry helps detect:
- Acute angle closure
- Steroid response
- Uveitic pressure changes
- Postoperative pressure elevation
- Secondary glaucoma
Pressure measurement may be avoided initially when an open-globe injury is suspected.
Dilated Examination
Dilation may be required to examine:
- Retina
- Vitreous
- Optic nerve
- Posterior inflammation
- Trauma-related damage
- Endophthalmitis
Corneal Cultures or Scrapings
Microbiological testing may be required for:
- Large ulcers
- Central infection
- Severe infection
- Contact-lens-related disease
- Fungal or Acanthamoeba concern
- Atypical appearance
- Poor response to initial treatment
Imaging and Blood Tests
Depending on the findings, additional tests may include:
- Anterior-segment OCT
- Corneal imaging
- Retinal OCT
- Ultrasound
- CT of the orbit and sinuses
- MRI
- Blood count
- Inflammatory markers
- Autoimmune investigations
- Infectious-disease testing
Can a Red Eye Be Diagnosed from a Photograph?
A photograph may show the distribution of redness, discharge or swelling.
It cannot reliably determine:
- Corneal staining
- Anterior-chamber inflammation
- Eye pressure
- Pupil reactions
- Optic-nerve function
- A small corneal ulcer
- Orbital involvement
- The depth of scleral inflammation
A normal-looking photograph does not exclude a serious painful or vision-threatening condition.
What Can Be Done Safely at Home?
For mild bilateral irritation without red flags:
- Stop contact-lens wear.
- Avoid rubbing the eyes.
- Use preservative-free artificial tears.
- Apply a cool compress for allergy.
- Maintain eyelid hygiene when blepharitis is present.
- Avoid smoke, dust and direct airflow.
- Wash hands regularly.
- Avoid sharing towels or cosmetics.
- Take breaks from prolonged screen use.
Home care should not delay assessment when the eye is painful, photophobic or visually affected.
What Should Not Be Done?
Do not:
- Use leftover steroid drops.
- Share another person’s eye medication.
- Continue wearing contact lenses.
- Cover a painful contact-lens eye with a patch.
- Use tap water as contact-lens solution.
- Rub an injured eye.
- Attempt to remove an embedded object.
- Delay irrigation after chemical exposure.
- Use redness-relief drops to conceal persistent inflammation.
- Assume every red eye is conjunctivitis.
Why Are Steroid Eye Drops Potentially Dangerous?
Steroids may:
- Worsen herpes simplex keratitis
- Worsen fungal infection
- Delay epithelial healing
- Raise eye pressure
- Cause cataract with prolonged use
- Mask progression of infection
They are valuable for properly diagnosed inflammatory conditions but should be used under medical supervision. HealthHub notes that ophthalmic corticosteroids treat several inflammatory conditions but require appropriate precautions and monitoring.
How Is a Red Eye Treated?
Treatment depends on the cause.
Possible treatments include:
- Artificial tears
- Eyelid hygiene
- Antihistamine drops
- Antibiotic drops or ointment
- Antiviral medication
- Antifungal or anti-Acanthamoeba treatment
- Anti-inflammatory drops
- Pressure-lowering medication
- Foreign-body removal
- Corneal protection
- Retinal or glaucoma laser
- Intravenous antibiotics
- Surgery
- Treatment of an underlying autoimmune disease
There is no single “red-eye drop” suitable for every diagnosis.
Frequently Asked Questions
Is a red eye always infectious?
No.
Dry eye, allergy, haemorrhage, episcleritis, scleritis, uveitis, glaucoma and trauma can all cause redness without contagious infection.
How can I tell viral from bacterial conjunctivitis?
Viral disease is more often watery and associated with respiratory symptoms.
Bacterial disease is more often associated with thick discharge and eyelid crusting.
There is substantial overlap, and examination may be needed.
Does green discharge always mean bacterial infection?
It makes bacterial infection more likely but is not completely diagnostic.
Does itching mean allergy?
Prominent itching strongly favours allergy, but allergy may coexist with dry eye or infection.
Can dry eye make the eyes very red?
It can, particularly when severe or associated with medication toxicity.
Marked one-sided redness, pain or visual reduction still requires assessment.
Why is only one eye red?
Possible causes include:
- Foreign body
- Abrasion
- Keratitis
- Uveitis
- Episcleritis
- Scleritis
- Acute glaucoma
- Trauma
- Early conjunctivitis
- Herpes infection
Why are both eyes red?
Possible causes include:
- Viral conjunctivitis
- Allergy
- Dry eye
- Blepharitis
- Environmental irritation
- Medication reaction
Does a bright-red patch mean the eye is bleeding internally?
Usually, a painless patch on the white of the eye is a subconjunctival haemorrhage.
Blood inside the central or coloured portion of the eye after trauma is different and requires urgent care.
Why is the red patch getting larger?
Blood may spread beneath the conjunctiva before it begins to resolve.
Pain, visual loss or significant trauma still requires examination.
Can a subconjunctival haemorrhage affect vision?
An uncomplicated haemorrhage should not reduce vision.
Visual change suggests another condition or injury.
Can I exercise with a subconjunctival haemorrhage?
Ordinary activity is generally safe when the diagnosis is confirmed and there was no significant trauma.
Repeated haemorrhages may warrant blood-pressure and medical review.
Is a painful red eye glaucoma?
Acute angle closure is one important possibility, but corneal infection, uveitis and scleritis may present similarly.
Does chronic glaucoma cause redness?
Not usually.
The redness may instead be due to medication, dry eye or another eye condition.
Can cataract cause a red eye?
Ordinary age-related cataract is painless and does not cause redness.
Can retinal detachment cause redness?
Retinal detachment is usually painless and does not commonly produce a red eye.
Can migraine cause a red eye?
Migraine may cause eye watering or facial autonomic symptoms, but a markedly red painful eye with visual change requires examination.
Can sinusitis make the eye red?
Sinus infection may contribute to eyelid or orbital inflammation.
Redness with swelling, fever, pain on eye movement, double vision or proptosis requires emergency care.
Can contact-lens irritation settle after lens removal?
Minor dryness may improve.
Pain, photophobia, blur or persistent redness after removal requires urgent examination.
Can I wear my lenses again once the redness improves?
Do not resume lens wear until:
- The cause has been established
- The eye is white and comfortable
- Vision is normal
- Treatment has been completed
- The eye-care professional approves
Replace potentially contaminated lenses and cases when instructed.
Can artificial tears treat conjunctivitis?
They may improve comfort and rinse surface irritants but do not treat every infection.
Can I use antibiotic drops preventively?
Routine use is not recommended without a clinical indication.
Can I use antihistamine drops for any red eye?
No.
They help allergy but do not treat infection, uveitis, keratitis or acute glaucoma.
Why did the clinic dilate my red eye?
Dilation may be needed to examine the retina, optic nerve, vitreous or posterior inflammation.
It may also help treat pain from selected cases of uveitis.
Can pupil dilation worsen a narrow angle?
In anatomically susceptible eyes, dilation can rarely precipitate angle closure.
The clinician assesses the risk and monitors symptoms.
Why is my eye still red after the infection has improved?
Persistent redness may result from:
- Ongoing inflammation
- Dry eye
- Medication toxicity
- Corneal involvement
- Blepharitis
- Slow vascular recovery
- An incorrect diagnosis
Can red eyes be caused by an autoimmune disease?
Yes.
Autoimmune disease may be associated with:
- Dry eye
- Episcleritis
- Scleritis
- Uveitis
- Peripheral corneal inflammation
- Orbital inflammation
When should recurrent red eyes be investigated?
Assessment is appropriate when episodes:
- Are repeatedly one-sided
- Are painful
- Cause photophobia or blur
- Occur with joint, skin, bowel or respiratory symptoms
- Respond only temporarily to treatment
- Are associated with steroid dependence
A Practical Urgency Guide
Emergency Care Now
- Chemical exposure
- Penetrating or high-velocity trauma
- Severe pain with reduced vision
- Painful red eye with halos, headache, nausea or vomiting
- Contact-lens-related redness with pain or blur
- Severe postoperative or post-injection pain and redness
- Eyelid swelling with fever, proptosis or painful restricted movement
- A cloudy cornea or new white corneal spot
Same-Day or Prompt Eye Assessment
- Moderate pain
- Significant photophobia
- Persistent one-sided redness
- Reduced vision
- Corneal foreign-body sensation
- New redness after eye surgery
- A forehead or eyelid blistering rash
- Recurrent deep redness
- Symptoms that worsen despite treatment
Routine Assessment May Be Appropriate
- Mild bilateral itching
- Mild watery redness
- Stable dry-eye symptoms
- Mild blepharitis
- Painless isolated subconjunctival haemorrhage with normal vision
Any development of pain, photophobia or visual change moves the condition into a more urgent category.
A Practical Clinical Approach
Step 1: Check Vision
Test each eye separately.
A true reduction in vision is a major red flag.
Step 2: Ask About Pain and Photophobia
These symptoms suggest corneal, intraocular or deeper inflammation rather than uncomplicated surface conjunctivitis.
Step 3: Review Contact-Lens Use
A painful red eye in a contact-lens wearer is considered keratitis until examination proves otherwise.
Step 4: Assess the Pattern of Redness
- Diffuse conjunctival
- Circumcorneal
- Localised patch
- Deep bluish-red
- Associated swelling
Step 5: Examine the Cornea
Look for:
- Abrasion
- Ulcer
- Infiltrate
- Foreign body
- Herpetic pattern
- Wound leak
Step 6: Examine the Anterior Chamber and Pupil
Look for:
- Inflammatory cells
- Blood
- Abnormal pupil
- Angle-closure features
Step 7: Measure Eye Pressure
When safe and clinically appropriate.
Step 8: Assess Eyelids and Orbit
Look for:
- Blepharitis
- Cellulitis
- Proptosis
- Painful or restricted eye movement
Step 9: Treat the Specific Cause
Avoid treating redness alone without establishing which structure is affected.
Common Myths About Red Eyes
“Every red eye is conjunctivitis.”
False.
Corneal infection, uveitis, scleritis and acute glaucoma may look similar but require very different treatment.
“If there is discharge, the condition cannot be serious.”
False.
Corneal and postoperative infections may also produce discharge.
“If the eye does not hurt, it is harmless.”
False.
Some important conditions cause limited pain, particularly when corneal sensation is reduced.
“A very dramatic red patch means the eye is badly damaged.”
False.
A painless subconjunctival haemorrhage often looks alarming but is usually harmless.
“Steroid drops are the fastest treatment for redness.”
False.
They can worsen certain infections and raise eye pressure.
“Contact-lens wearers can wait a day or two after removing the lens.”
False.
Microbial keratitis may progress rapidly and threaten vision.
“Redness-relief drops cure the problem.”
False.
They temporarily constrict vessels without treating the cause.
“Clear vision means the cornea is healthy.”
False.
A small peripheral corneal ulcer may initially spare central acuity.
“Both eyes being red proves it is contagious.”
False.
Allergy, dry eye and medication reactions often affect both eyes.
The Bottom Line
Red eye is a symptom with many possible causes.
Common and usually less dangerous causes include:
- Dry eye
- Blepharitis
- Allergy
- Mild viral or bacterial conjunctivitis
- Subconjunctival haemorrhage
- Episcleritis
Potentially sight-threatening causes include:
- Corneal infection
- Contact-lens-related keratitis
- Herpes eye disease
- Uveitis
- Scleritis
- Acute angle closure
- Chemical injury
- Significant trauma
- Postoperative infection
- Orbital cellulitis
The most important warning signs are:
- Pain
- Photophobia
- Reduced vision
- Contact-lens use
- Corneal clouding or a white spot
- Headache, halos, nausea or vomiting
- Trauma or chemical exposure
- Recent eye surgery or injection
- Fever, proptosis or painful eye movement
A red eye should not be judged by redness alone. A mildly pink eye may be harmless, while a less dramatic eye with pain, photophobia or visual loss may represent a sight-threatening emergency.
References
- National Eye Institute. Pink Eye and Other Conjunctival Conditions.
- Singapore HealthHub. Eye Infections.
- Singapore HealthHub. Allergic Conjunctivitis. Updated December 2024.
- National Health Service. Eye Pain and Red-Eye Warning Symptoms.
- Moorfields Eye Hospital. Red Eyes and Red Flags—When to Refer.
- National Eye Institute. Corneal Conditions. Updated August 2025.
- Centers for Disease Control and Prevention. Contact-Lens-Related Eye Infections. Updated May 2025.
- Centers for Disease Control and Prevention. Acanthamoeba Keratitis. Updated June 2025.
- National Health Service. Uveitis.
- American Academy of Ophthalmology. What Is Scleritis? Updated January 2026.
- Singapore HealthHub. Glaucoma.
- American Academy of Ophthalmology. Subconjunctival Haemorrhage.
- National Health Service. Eye Injuries and Chemical Exposure.
- National Eye Institute. Herpes Zoster Ophthalmicus and Recurrent Eye Disease.
- Manchester University NHS Foundation Trust. Periorbital and Orbital Cellulitis.
