Differential the causes of red eye
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I now have comprehensive data from multiple authoritative sources. Let me compile the full differential diagnosis of red eye.
Differential Diagnosis of Red Eye
Red eye is one of the most common presenting complaints in both primary care and emergency settings. The differential is broad, and the key to narrowing it is assessing: pain, visual acuity, photophobia, discharge type, pattern of injection, corneal appearance, pupil size, and IOP.
Anatomical Framework (Wills Eye Manual)
1. Adnexal Causes
- Trichiasis / distichiasis (inturned lashes rubbing the cornea)
- Floppy eyelid syndrome
- Entropion / ectropion
- Lagophthalmos (incomplete eyelid closure)
- Blepharitis / meibomitis
- Acne rosacea (sebaceous gland dysfunction)
- Dacryocystitis (lacrimal sac infection)
- Canaliculitis
2. Conjunctival Causes
- Conjunctivitis - the most common cause overall:
- Bacterial: purulent discharge, diffuse injection, lids stuck in morning
- Viral: watery discharge, preauricular lymphadenopathy, often follows URI
- Allergic: intense itching, bilateral, stringy white discharge, chemosis
- Atopic / Vernal: cobblestone papillae on upper tarsal plate, chronic
- Giant papillary conjunctivitis: contact lens wearers
- Chemical / toxic: history of exposure, medication toxicity
- Subconjunctival hemorrhage: bright red flat patch, painless, no visual loss
- Inflamed pinguecula / pterygium
- Superior limbic keratoconjunctivitis
- Symblepharon (mucous membrane pemphigoid, Stevens-Johnson syndrome, toxic epidermal necrolysis)
- Conjunctival neoplasia
- Ophthalmia neonatorum (in infants)
3. Corneal Causes
- Corneal abrasion: acute pain, foreign body sensation, watery discharge, visible on fluorescein staining
- Corneal foreign body: localized injection, visible FB
- Infectious keratitis:
- Bacterial: contact lens wearers, corneal ulcer with hypopyon
- Viral (HSV): dendritic ulcer on fluorescein, decreased corneal sensation
- Fungal: trauma with plant material, feathery edges
- Acanthamoeba: contact lens + water exposure, severe pain out of proportion
- Ultraviolet keratitis (snow blindness, welder's arc eye): onset 6-12 hrs after UV exposure, punctate lesions
- Recurrent corneal erosion: sudden pain on waking
- Neurotrophic keratopathy
- Chemical / alkali burn (emergency - alkali penetrates deeper than acid)
- Pterygium
- Contact lens-related problems
4. Other / Deeper Causes
| Condition | Key Features |
|---|---|
| Anterior uveitis (iritis/iridocyclitis) | Circumcorneal (ciliary) flush, photophobia, miotic pupil, keratic precipitates, cells/flare in anterior chamber, blurred vision, normal or low IOP |
| Acute angle-closure glaucoma | EMERGENCY - severe pain, nausea/vomiting, halos around lights, markedly blurred vision, fixed mid-dilated pupil, rock-hard eye, corneal haze, markedly elevated IOP |
| Episcleritis | Localized or diffuse redness, mild discomfort, normal vision, blanches with phenylephrine drops |
| Scleritis | Severe deep boring pain, tenderness, does NOT blanch, associated with systemic autoimmune disease (RA, SLE, GPA), risk of scleral perforation |
| Endophthalmitis | Post-surgical or post-traumatic, severe pain, hypopyon, very poor vision - ocular emergency |
| Trauma | History, may include hyphema, ruptured globe |
| Carotid-cavernous fistula | Pulsating exophthalmos, corkscrew conjunctival vessels, raised episcleral venous pressure |
| Cluster headache | Unilateral conjunctival injection + lacrimation, severe periorbital pain, Horner's syndrome |
| Dry eye syndrome | Chronic, burning/gritty, worsens through day, Schirmer's test reduced |
| Pharmacologic | Prostaglandin analogs (e.g., latanoprost) cause conjunctival hyperemia |
Classic Comparison Table
| Feature | Bacterial Conjunctivitis | Viral Conjunctivitis | Anterior Uveitis (Iritis) | Keratitis | Acute Angle-Closure Glaucoma |
|---|---|---|---|---|---|
| Vision | Normal | Normal | Blurred | Blurred | Markedly blurred |
| Pain | None / irritation | Mild | Moderate-severe, stabbing | Sharp, severe | Severe + nausea/vomiting |
| Photophobia | None | Mild | Moderate | Moderate | Moderate |
| Discharge | Purulent, yellow-green | Watery / serous | None | None to mild watery | None |
| Itching | No | No | No | No | No |
| Injection pattern | Diffuse | Diffuse | Circumcorneal (ciliary flush) | Circumcorneal | Diffuse |
| Cornea | Clear | Clear | Clear | Cloudy / ulcer | Hazy |
| Pupil | Normal | Normal | Constricted (miosis) | Normal | Fixed mid-dilated |
| IOP | Normal | Normal | Normal or low | Normal | Markedly elevated |
(Adapted from Textbook of Family Medicine 9e, Table 17-1)
Danger Signs Requiring Urgent Ophthalmology Referral
Any red eye with the following features is a red flag:
- Reduced visual acuity
- Moderate-to-severe pain
- Photophobia
- Corneal staining / opacity
- Corneal edema
- Unequal pupils
- Elevated IOP
- Hypopyon (pus in anterior chamber)
- Proptosis or chemosis
- History of penetrating trauma
If none of these are present, conjunctivitis is the most likely diagnosis.
Quick Mnemonic by Injection Pattern
- Diffuse injection (all quadrants, vessels branch from periphery centrally): conjunctivitis, subconjunctival hemorrhage, dry eye, chemical
- Circumcorneal / ciliary flush (red ring around cornea, deep vessels, no branching): uveitis, keratitis, acute glaucoma - all more serious
- Localized injection: episcleritis, pterygium, inflamed pinguecula, foreign body
Sources: Wills Eye Manual 7e, p. 42 | Textbook of Family Medicine 9e, p. 347 | Tintinalli's Emergency Medicine, Table 241-3 | Goldman-Cecil Medicine, Table 391-3/4
Causes of red eye how toh differenciate to each other
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I now have all the data needed to build a thorough, clinically useful differentiation guide. Let me compile this comprehensively.
How to Differentiate the Causes of Red Eye
The key clinical parameters to systematically assess are:
Pain → Vision → Photophobia → Discharge → Injection pattern → Cornea → Pupil → IOP
STEP 1 - Start with the Most Important Question: Is Vision Affected?
| Vision Normal | Vision Reduced |
|---|---|
| Conjunctivitis (bacterial, viral, allergic) | Keratitis |
| Subconjunctival hemorrhage | Anterior uveitis (iritis) |
| Episcleritis | Acute angle-closure glaucoma |
| Blepharitis | Chemical burn |
| Dry eye | Endophthalmitis |
| Hordeolum / chalazion | Scleritis (severe cases) |
Rule: The triad of red eye + pain + loss of vision always signals a potentially blinding condition requiring urgent ophthalmology referral. - Textbook of Family Medicine 9e, p. 348
STEP 2 - The Master Differentiation Table
| Feature | Bacterial Conjunctivitis | Viral Conjunctivitis | Allergic Conjunctivitis | Anterior Uveitis (Iritis) | Keratitis | Acute Angle-Closure Glaucoma | Episcleritis | Scleritis | Subconjunctival Hemorrhage |
|---|---|---|---|---|---|---|---|---|---|
| Pain | None / irritation | Mild / gritty | None / itching | Moderate-severe, intermittent stabbing | Sharp, severe | Severe + headache, N&V | Mild discomfort | Severe, deep, boring | None |
| Itching | No | No | YES (hallmark) | No | No | No | No | No | No |
| Photophobia | None | Mild | None | Moderate | Moderate | Moderate | None | None | None |
| Vision | Normal | Normal | Normal | Blurred | Blurred | Markedly blurred | Normal | Normal (usually) | Normal |
| Discharge | Purulent, yellow-green | Watery / serous | Stringy, white, mucoid | None | None to mild watery | None | None | None | None |
| Injection pattern | Diffuse (peripheral > central) | Diffuse | Diffuse + chemosis | Circumcorneal (ciliary flush) | Circumcorneal | Diffuse | Localized sector | Deep red-purple, does NOT blanch with phenylephrine | Flat, bright red patch |
| Cornea | Clear | Clear | Clear | Clear | Cloudy / ulcer / dendrite | Hazy / edematous | Clear | Clear | Clear |
| Pupil | Normal | Normal | Normal | Constricted (miosis) | Normal | Fixed mid-dilated | Normal | Normal | Normal |
| IOP | Normal | Normal | Normal | Normal or LOW | Normal | MARKEDLY HIGH | Normal | Normal | Normal |
| Laterality | Usually bilateral (one eye first) | Bilateral (second eye follows) | Bilateral | Usually unilateral | Unilateral | Unilateral | Unilateral | Unilateral | Unilateral |
| Systemic features | None | URI, fever, adenopathy | Atopy, hay fever | HLA-B27 diseases (AS, IBD, Reiter's) | Contact lens use, trauma | Nausea, vomiting | Occasional autoimmune | RA, GPA, SLE, ANCA vasculitis | Valsalva, trauma, bleeding disorders |
STEP 3 - Key Distinguishing Features Per Condition
1. Bacterial Conjunctivitis
- Hallmark: Mucopurulent yellow-green discharge, lids stuck together on waking ("morning gluing")
- Diffuse conjunctival injection, papillae on tarsal plate
- Common organisms: S. aureus, S. pneumoniae, H. influenzae; in neonates: N. gonorrhoeae, C. trachomatis
- Vision normal, no photophobia, no corneal involvement
2. Viral Conjunctivitis
- Hallmark: Watery discharge + preauricular lymphadenopathy (absent in bacterial)
- Often follows a cold/URI, highly contagious
- Follicles (not papillae) on lower tarsal plate
- Subepithelial infiltrates may develop (adenovirus)
- Self-limiting over 2-3 weeks
3. Allergic Conjunctivitis
- Hallmark: Intense bilateral itching - the most discriminating symptom
- Stringy white mucoid discharge, chemosis (conjunctival swelling)
- Cobblestone papillae on upper tarsal plate (vernal / atopic)
- Associated with atopy (asthma, eczema, hay fever)
- Seasonal or perennial pattern
4. Anterior Uveitis (Iritis / Iridocyclitis)
- Hallmark: Circumcorneal (ciliary) flush + photophobia + miotic pupil
- Deep aching/stabbing pain, worsens with light (consensual photophobia - pain on shining light in the OTHER eye is positive)
- Slit-lamp: keratic precipitates (KPs) on corneal endothelium, cells and flare in anterior chamber
- Pupil irregular / constricted due to posterior synechiae
- IOP normal or LOW (ciliary body inflammation reduces aqueous production)
- Associated systemic diseases: ankylosing spondylitis, HLA-B27, IBD, Reiter's, sarcoidosis, JIA
5. Keratitis (Corneal Inflammation)
- Hallmark: Severe sharp pain + corneal opacity visible to naked eye
- Fluorescein staining reveals epithelial defect
- Types:
- Bacterial: contact lens wearer, dense white ulcer, hypopyon (pus in anterior chamber)
- HSV (herpetic): branching dendritic ulcer on fluorescein, reduced corneal sensation (test with wisp of cotton)
- Acanthamoeba: contact lens + tap water/swimming, disproportionate pain
- Fungal: feathery edges, trauma with plant material
- UV keratitis (welder's flash / snow blindness): punctate lesions, delayed onset 6-12 hrs post UV exposure, bilateral severe pain
6. Acute Angle-Closure Glaucoma (EMERGENCY)
- Hallmark: Rock-hard eye + fixed mid-dilated pupil + halos around lights
- Sudden severe pain, frontal headache, nausea and vomiting (can mimic GI emergency)
- Shallow anterior chamber on oblique illumination (shadow on far iris)
- Corneal haze / steamy appearance
- IOP markedly elevated (>40 mmHg, sometimes >60)
- Risk factors: hypermetropia (small eye), elderly, dim lighting / dilating drops triggers attack
- Treatment is urgent: IV/IM acetazolamide 500 mg, topical pilocarpine, glycerin, immediate ophthalmology referral
7. Episcleritis vs. Scleritis
| Feature | Episcleritis | Scleritis |
|---|---|---|
| Pain | Mild discomfort | Severe, deep, boring, wakes from sleep |
| Appearance | Superficial, bright red, localized sector | Deep red-purple / violaceous hue |
| Phenylephrine blanching test | Blanches (superficial vessels) | Does NOT blanch (deep scleral vessels) |
| Nodules | Possible (nodular type) | Possible (nodular anterior scleritis) |
| Vision | Normal | May be reduced |
| Systemic disease | Occasional | ~50% have systemic disease (RA, GPA, SLE, ANCA vasculitis) |
| Tenderness | Mild | Marked tenderness on gentle palpation |
| Self-limiting | Yes, usually | No - requires systemic NSAIDs / immunosuppression |
8. Subconjunctival Hemorrhage
- Hallmark: Sharply demarcated, flat, bright red patch under conjunctiva - looks alarming but is benign
- Completely painless, vision normal, no discharge
- Caused by: Valsalva (coughing, straining), trauma, bleeding disorders, hypertension, anticoagulants
- Resolves spontaneously over 1-2 weeks (turns yellow-green like a bruise)
- No treatment needed - reassure the patient
9. Blepharitis
- Hallmark: Morning crusting / scaling at lid margins, eyelashes involved
- Gritty/burning sensation, worse on waking
- Staphylococcal: collarette scales around lashes, posterior margin involvement
- Associated with: meibomitis, acne rosacea, seborrhoea
- Chronic, recurrent; treated with lid hygiene + warm compresses
10. Dacryocystitis
- Hallmark: Localized pain and swelling at the medial canthus (inner corner of eye)
- Pus expressible from lacrimal punctum on pressure over lacrimal sac
- Epiphora (tearing) + mucopurulent discharge from the punctum
- May have fever if severe (systemic infection)
- Caused by nasolacrimal duct obstruction
STEP 4 - Discharge Type is a Quick Discriminator
| Discharge Type | Cause |
|---|---|
| Purulent (yellow-green, creamy) | Bacterial conjunctivitis |
| Watery / serous | Viral conjunctivitis |
| Stringy, white, mucoid | Allergic conjunctivitis |
| Morning crusting / scaling at lid margin | Blepharitis |
| No discharge | Uveitis, angle-closure glaucoma, scleritis, UV keratitis |
STEP 5 - Injection Pattern at a Glance
Diffuse injection (all quadrants, branching from periphery inward)
→ Conjunctivitis, dry eye, chemical, subconjunctival hemorrhage
Circumcorneal / ciliary flush (red ring around limbus, no branching)
→ Uveitis, keratitis, acute glaucoma ← MORE SERIOUS
Localized / sectoral
→ Episcleritis, pterygium, foreign body, inflamed pinguecula
RED FLAGS - Refer to Ophthalmology Urgently if ANY Present
- Reduced visual acuity
- Moderate to severe pain
- Photophobia
- Corneal opacity / staining
- Ciliary flush (circumcorneal injection)
- Unequal or irregular pupils
- Elevated IOP (hard eye)
- Hypopyon (pus level in anterior chamber)
- Proptosis or chemosis
- Penetrating trauma history
Sources: Wills Eye Manual 7e, p. 42 | Textbook of Family Medicine 9e, pp. 347-348 | Tintinalli's Emergency Medicine, Table 241-3 | Rheumatology 2-Volume Set, p. 239 | Goldman-Cecil Medicine, Tables 391-3/4
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