Summary: A common, self-limiting infection of the conjunctival mucous membrane. Characterised by mucopurulent discharge and conjunctival injection. While mostly benign, it must be distinguished from sight-threatening causes of "Red Eye" (Keratitis, Uveitis, Glaucoma).

Key Facts

• Prevalence: Very common in children and elderly.
• Microbiology: Staphylococcus aureus (Adults), Streptococcus pneumoniae + Haemophilus influenzae (Children).
• Course: 60% resolve without treatment in 5 days.
• Contact Lenses: A "Red Eye" in a contact lens wearer is Microbial Keratitis (Pseudomonas) until proven otherwise.

The "Golden Rules"

1. Check Vision: Always document Visual Acuity. If reduced, it's NOT simple conjunctivitis.
2. Fluorescein: Stain every red eye to rule out corneal ulcers/abrasions.
3. No Steroids: Never prescribe topical steroids (e.g., Maxitrol) in primary care. They can worsen Herpes Simplex Keratitis ("Amoeboid Ulcer").

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Pathogen	Demographic	Features	Severity
Staph aureus	Adults	Chronic, recurrent, associated with Blepharitis.	Mild
Strep pneumoniae	Children	"Glue Ear" of the eye. Often concurrent Otitis Media.	Moderate
Haemophilus	Children	"Conjunctivitis-Otitis Syndrome".	Moderate
Moraxella	Elderly/Immunocompromised	Chronic follicular conjunctivitis.	Mild
Pseudomonas	Contact Lens Wearers	AGGRESSIVE. Melts cornea in 24 hours.	SEVERE
Neisseria gonorrhoeae	Sexual / Neonatal	HYPERACUTE. Massive pus. Cornea perforates quickly.	EMERGENCY

Fungal Keratitis

The Farmer's Eye.

• Cause: Candida (Yeast) or Fusarium/Aspergillus (Filamentous).
• Risk: Trauma with vegetable matter (branch/leaf) or Chronic steroid drops.
• Sign: "Feathery" edges to the ulcer. Satellite lesions.
• Treatment: Natamycin / Amphotericin B. Hard to treat.

| Chlamydia | YA / Neonatal | Chronic (> weeks). Follicles. "Ophthalmia Neonatorum". | Moderate |

Trachoma (Chlamydia trachomatis A-C)

The leading cause of infectious blindness.

• Demographic: Developing world (flies, poor water).
• Mechanism: Chronic re-infection -> Scarring of underside of lid -> Entropion (Lashes turn in) -> Corneal Scratches -> Blindness.
• SAFE Strategy: Surgery, Antibiotics (Azithromycin), Facial cleanliness, Environmental.

Acanthamoeba Keratitis

The Contact Lens Nightmare.

• Source: Tap water / Swimming pools / Hot tubs.
• Sign: Ring abscess. Disproportionate PAIN.
• Treatment: Pool cleaner (PHMB)! Takes months/years to cure.

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History

• Onset: Acute (<24 hours).
• Discharge: Thick, yellow/green, purulent. "Stuck together in the morning".
• Laterality: Often starts in one eye, spreads to the other in 24-48 hours (via hands/pillow).
• Pain: None or mild grit/sand sensation. (Severe pain = Red Flag).
• Vision: Normal (maybe slightly blurred by gunk, clears with blinking).

Examination

• Injection: Generalised, diffuse redness.
• Discharge: Purulent exudate at lid margins/canthus.
• Cornea: Clear. No uptake with fluorescein.
• Pupils: Round, reactive.
• Lids: Mild oedema (chemosis) is common.

Clinical Investigation: Visual Acuity (VA)

The Vital Sign of the Eye.

• Method: Snellen Chart at 6 metres (or 3 metres with mirror).
• Notation: 6/6 (Normal), 6/9, 6/12, 6/60.
• Pinhole: If VA is reduced (e.g., 6/12), ask patient to look through a pinhole.
  • Improvement: Refractive Error (Needs glasses).
  • No Improvement: Pathology (Cataract, Macula, or Corneal Opacity).
• Rule: If VA is <6/9 and no improvement with pinhole -> REFER.

Differential Diagnosis Table

Feature	Bacterial	Viral (Adenovirus)	Allergic	Acute Glaucoma
Discharge	Purulent (Pus)	Watery / Serous	Stringy / Mucoid	None
Itch	Minimal	Minimal	SEVERE	None
Nodes	No	Pre-auricular (Tender)	No	No
Systemic	Occasional Earache	Recent Cold / Sore Throat	Atopy History	Nausea/Vomiting
Vision	Normal	Normal	Normal	Halos / Blurred
Pain	Gritty	Gritty	Gritty	Deep Ache / Headache

Viral Conjunctivitis (Adenovirus)

The "Cold in the Eye".

• Highly Contagious: Can survive on surfaces for weeks.
• Signs: Watery, Follicles on lid (white bumps), Pre-auricular node (tender bump in front of ear).
• Course: Gets worse for 5 days, then better over 2 weeks.
• Betadine Protocol: Some specialists use dilute Betadine wash (off-label) to kill virus.
• Steroids: If cornea involved (Sub-epithelial infiltrates), may need weak steroid (Under Specialist).

Advanced Microbiology: The Adenovirus

The commonest cause of red eye worldwide.

• Serotypes 8, 19, 37: Cause Epidemic Keratoconjunctivitis (EKC). Severe, pseudomembranes, corneal scars.
• Serotypes 3, 7: Cause Pharyngoconjunctival Fever (PCF). Sore throat + Fever + Red Eye (Kids/Swimming pools).
• Enterovirus 70: Causes Acute Haemorrhagic Conjunctivitis (Blood everywhere).

Herpes Simplex Keratitis (HSV)

The Dendritic Ulcer.

• Cause: Reactivation of HSV-1 (Cold sore virus) in Trigeminal nerve.
• Sign: Branching "Tree-like" ulcer on cornea (Stains with Fluorescein).
• Treatment: Topical Acyclovir (Zovirax). NEVER STEROIDS (Fuels the fire).

Herpes Zoster Ophthalmicus (Shingles)

The belt of fire.

• Sign: Rash on forehead (V1 dermatome).
• Hutchinson's Sign: Vesicle on tip of nose = High risk of eye involvement (Nasociliary nerve).
• Treatment: Oral Acyclovir (800mg 5x/day).

Allergic Conjunctivitis Types

1. Seasonal (Hayfever): Pollen. Itchy +++.
2. Perennial: Dust mites. Year-round.
3. Vernal (VKC): Boys 5-15 years. Giant papillae (Cobblestones). Sight threatening (Shield ulcers).
4. Giant Papillary (GPC): Contact lens reaction to protein deposits.

The "Red Eye" Differential Diagnosis

The "Red Eye" Differential Diagnosis

What NOT to miss.

• Iritis (Anterior Uveitis): Photophobia + Pain + Small Pupil.
• Acute Glaucoma: Haloes + Headache + Fixed Mid-dilated Pupil + Cloudy Cornea.
• Scleritis: Deep, boring pain (wakes patient at night). Violet hue. Associated with Rheumatoid Arthritis.
• Episcleritis: Segmental redness. Mild pain. Self-limiting.
• Subconjunctival Haemorrhage: Bright red blood patch. Painless. "Bruise of the eye". Benign.

The Great Mimic: Dry Eye Syndrome

It feels like sand, but it's not infection.

• Mechanism: Tear film instability -> Nerve exposure -> Reflex tearing (Watery eye).
• Paradox: "My eye is watering, how can it be dry?" -> The tears produced are poor quality (watery, no oil).
• Signs: Reduced Tear Break Up Time (TBUT <10s). Punctate Epithelial Erosions (PEE) on fluorescein.
• Treatment: Lubricants (Drops associated with Hyaluronic Acid), Warm Compresses.

Systemic Associations (The "Reactive" Eye)

• Reiter's Syndrome: "Can't see, Can't pee, Can't climb a tree". Conjunctivitis + Urethritis + Arthritis. (Chlamydia trigger).
• Stevens-Johnson Syndrome: Mucosal blistering. Emergency.
• Sjogren's Syndrome: Dry eyes + Dry mouth (Autoimmune).
• Rosacea: Chronic Blepharitis/Conjunctivitis (Ocular Rosacea).

Exam Pearls: How to look like a Pro

1. Flip the Lid: Essential for suspected foreign body. Use a cotton bud.
2. The Pre-Auricular Node: Palpate just in front of the tragus. If tender -> VIRAL or CHLAMYDIA. Bacterial does NOT cause nodes.
3. Fluorescein Pattern:
   • Dendrite: Herpes.
   • Punctate (Dots): Dry eye / Viral / Toxicity.
   • Geography: Abrasion.
   • Pooling: Ulcer.
4. Pinholes: If vision is reduced, use a pinhole. If it improves -> Refractive error (Glasses need). If not -> Pathology.

To Swab or Not to Swab?

• Standard Cases: Do NOT swab. It is a clinical diagnosis.
• Indications for Swab:
  1. Neonates (Ophthalmia Neonatorum is a notifiable disease).
  2. Hyperacute (Suspect Gonorrhoea).
  3. Treatment Failure (After 1 week of correct drops).
  4. Recurrent (Suspect Chlamydia/Viral).

Public Health Notification

When to tell the authorities.

• Ophthalmia Neonatorum: NOTIFIABLE in the UK. (Public Health Act).
• Reason: To prevent blindness and trace Gonorrhoea contacts.
• Action: Fill out the NOIDS (Notification of Infectious Diseases) form.
• Viral Outbreaks: EKC in a school/hospital/barracks must be reported to Infection Control.

Contact Lens Protocol

• Rule: ANY red eye in a CL wearer -> REFER TO OPHTHALMOLOGY/CASUALTY.
• Reason: High risk of Pseudomonas Keratitis.
• Action: Stop lens wear immediately. Do not discard the lens/case (culture them).

When to Refer (The Red Flags Revisited)

Don't sit on these.

1. Neonates: Same day referral ( Paeds/Ophth).
2. Contact Lens Wearers: Same day (Casualty).
3. Pain/Photophobia: Same day (Uveitis/Glaucoma).
4. Visual Loss: Immediate.
5. Herpes Zoster: Same day (if tip of nose involved).
6. Corneal Opacity: Immediate (Ulcer).
7. Hyperacute (Pus everywhere): Immediate (Gonorrhoea).

Contact Lens Hygiene Facts

• Sleeping in Lenses: Increases infection risk by 10x.
• Tap Water: NEVER use tap water (Acanthamoeba risk - devastating).
• Swimming: Goggles or dailies (discard immediately).
• Case Replacement: Must replace case monthly (Biofilms form).

Clinical Vignette: The Student's Mistake

A cautionary tale.

• History: 21yo student ran out of solution, used tap water to store lenses.
• Presentation: Severe pain, photophobia, ring ulcer.
• Diagnosis: Acanthamoeba Keratitis.
• Outcome: 9 months of toxic drops (PHMB) every hour. Corneal transplant required.
• Lesson: NEVER USE TAP WATER.

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Conservative Management

The "Wait and See" approach.

• Rational: 65% of cases resolve alone in 2-5 days.
• Hygiene:
  • Wash hands frequently.
  • Separate towels/pillows (Highly contagious).
  • Clean discharge with cotton wool soaked in cooled boiled water.
• School: Do NOT exclude from school (Public Health England / CDC guidance). Similar infectivity to a common cold.
  • Letter for School: "Conjunctivitis does not require exclusion unless the child is unwell."
  • Nursery: Some nurseries have their own (incorrect) rules demanding treatment before return. Give Chloramphenicol to appease them.

Paediatric Pearls

• The "Sticky" Infant: If <1 year old and well -> likely Blocked Tear Duct. Massage the nose.
• The "Screaming" Toddler: Don't fight. Use the "Inner Corner" trick (Drop in closed eye).
• The "Recurrent" Child: Check for Glue Ear (Strep pneumo link).

Patient Handout: The "Do's and Don'ts"

DO:

• Wash hands before and after touching the eye.
• Use cool boiled water and cotton wool to clean crusts (wipe inward to outward, once only).
• Discard makeup (Mascara/Eyeliner) used during infection.
• Change pillowcases daily.

DON'T:

• Share towels or flannels.
• Wear contact lenses until 48 hours after the eye is completely white.
• Rub the eye (it spreads infection).
• Use breast milk (Old wives tale - sticking sugar in an eye is asking for bacterial growth).

Pharmacological (Topical Antibiotics)

For those who want a "quick fix" or moderate severity.

First Line: Chloramphenicol

• Form: Drops (0.5%) qds (Every 2-4 hours initially) or Ointment (1%) at night.
• Course: 5-7 days.
• Safety: Rare risk of Aplastic Anaemia (1 in 10 million). Safe in pregnancy (mostly).
• Note: Ointment blurs vision (greasy). Best for kids/night use.

Formulation Battle: Drops vs Ointment

Feature	Eye Drops (Gutt)	Eye Ointment (Oc)
Contact Time	Short (minutes)	Long (hours)
Vision	Clear	Blurred (Greasy)
Compliance	Hard (miss the eye)	Easy (wipe on lid?)
Preservatives	Yes (Stings)	No (Usually)
Best For	Daytime / Adults	Night / Children

Antibiotic Spectrum Table

Antibiotic	Class	Spectrum	Pros	Cons
Chloramphenicol	Amphenol	Broad (G+ and G-)	Cheap, OTC, Safe	Aplastic Anaemia risk (theoretical)
Fusidic Acid	Steroid-like structure	Staph Aureus	BD dosing (easy)	Resistance, Sticky
Gentamicin	Aminoglycoside	Gram Negatives	Potent	Toxicity (Epithelium)
Ofloxacin	Quinolone	Pseudomonas	High penetration	Resistance
Azithromycin	Macrolide	Chlamydia / Trachoma	Oral or Drop (Azyter)	Expense

Second Line: Fusidic Acid (Fucithalmic)

• Form: Viscous gel (1%) bd (Twice a day).
• Benefit: Better compliance (BD dosing). Good for Staph.
• Cons: Sticky. Resistance rising.

Third Line: Fluoroquinolones (Ofloxacin/Ciprofloxacin)

• Indication: Contact lens wearers (covers Pseudomonas) or severe cases.
• Setting: Usually Specialist use only.

The Pharmacy Shelf (OTC options)

• Golden Eye Ointment: Chloramphenicol 1%.
• Optrex Infected Eye: Chloramphenicol 0.5% drops.
• Brolene (Propamidine): Antiseptic. Weaker than antibiotics but covers Acanthamoeba (weakly).
• Lubricants: Hylo-Forte / Thealoz Duo. Wash out allergens/bacteria.

Advanced Management (Specialist Only)

• Topical Steroids (Dexamethasone/Prednisolone): Potent anti-inflammatory but risk of glaucoma/cataract/HSV flare.
• Cyclosporine (Ikervis): For severe Dry Eye or VKC.
• Systemic Immunosuppression: For Mucous Membrane Pemphigoid (Autoimmune conjunctivitis leading to scarring).

The "Chloramphenicol Debate"

1. Preparation: Wash hands. Tilt head back (or lie down).
2. The Pocket: Pull down the lower eyelid to create a "pocket".
3. The Drop: Squeeze one drop into the pocket. (The eye can only hold 20% of a drop, the rest runs down the face).
4. Occlusion: Press the inner corner (punctum) for 1 minute (Prevents systemic absorption and bad taste).
5. Child Trick: If they won't open eyes, put drop in the inner corner while closed. When they open, it falls in.

The "Chloramphenicol Debate"

• USA vs UK:
  • UK: Available Over-the-Counter (OTC). Standard of care.
  • USA: Rarely used due to theoretical Aplastic Anaemia risk. Prefer Erythromycin/Trimethoprim.
• Evidence: Meta-analyses show modest benefit (shortens duration by ~1 day).

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Ophthalmia Neonatorum

Sticky eyes in the first 28 days.

• Definition: Conjunctivitis in the first month of life.
• Causes:
  • Chemical (<24 hours): Silver nitrate reaction (historical).
  • Gonococcal (2-5 days): EMERGENCY. Hyperacute. Risk of corneal perforation. Rx: IV Ceftriaxone.
  • Chlamydial (5-14 days): Mucopurulent. Pneumonia risk. Rx: Oral Erythromycin.
  • Herpes (HSV): Vesicles. Rx: IV Acyclovir.
• Action: Hospital Referral is Mandatory.

The History of "Credé's Prophylaxis"

• The Problem: In the 19th Century, Gonorrhoea caused massive blindness in newborns.
• The Solution: Karl Credé (1881) introduced 2% Silver Nitrate drops at birth.
• The Result: Blindness dropped from 10% to 0.3%.
• Modern Era: Replaced by Erythromycin ointment (USA) or Povidone-Iodine.
• UK Policy: No prophylaxis. Treat if infection occurs (Screening for Chlamydia/Gonorrhoea in pregnancy is preferred).

Chlamydial Conjunctivitis (Adult Inclusion)

The sexually active red eye.

• Clue: "Chronic" conjunctivitis (>3 weeks) that doesn't respond to Chloramphenicol.
• Sign: Follicles (bumpy cobblestones) in the lower fornix.
• History: New partner? Urethritis?
• Rx: Systemic Doxycycline (Target the genital reservoir) + Topical.

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