Ocular Infections - Overview

Basic eye anatomy - Tietz Textbook of Laboratory Medicine, 7th Edition

1. Conjunctivitis ("Pink Eye")

Viral Conjunctivitis

• Most common type in adults
• Classic features: watery discharge, conjunctival redness, often starts in one eye and spreads bilateral
• May come with fever, runny nose, sore throat
• Adenoviruses account for up to 90% of viral cases - highly contagious
• Some adenovirus serotypes cause epidemic keratoconjunctivitis (involving the cornea), with symptoms lasting weeks to months
• HSV and VZV can also cause conjunctivitis and may extend to deeper eye structures
• Other causes: influenza, EBV, measles, mumps, molluscum contagiosum
• Treatment: Usually self-resolves within 2 weeks; supportive care

Bacterial Conjunctivitis

• More common in children than adults
• Typical organisms: Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis - in adults, S. aureus predominates
• Usually self-limited; benefit of topical antibiotics is debated but they are commonly prescribed

• Neisseria gonorrhoeae (and less often N. meningitidis)
• Copious, thick yellow-green discharge
• Requires systemic antibiotics (IM ceftriaxone), not just topical

• Chlamydia trachomatis - usually sexually acquired
• Trachoma (serotypes A, B, Ba, C) is the leading infectious cause of blindness worldwide - repeated infections cause eyelid scarring and corneal scarring
• Treatment: tetracycline eye ointment and/or oral azithromycin; oral doxycycline for genital chlamydia types

2. Keratitis (Corneal Infection)

Bacterial Keratitis

• Occurs with eye trauma, contact lens overwear, or corneal disease
• Organisms: Staphylococcus (including MRSA), Streptococcus, occasionally Mycobacterium
• Presents as a corneal ulcer - requires slit lamp examination to diagnose
• Treatment: topical fluoroquinolones (e.g., ciprofloxacin) as first-line; ideally after cultures taken from the ulcer
• Ophthalmology referral urgently needed

Herpes Simplex Keratitis

• Common corneal viral pathogen
• Classic finding: dendritic (branching) pattern on fluorescein staining
• Often recurs with any corneal stress (UV exposure, trauma, immunosuppression)
• Treatment: topical or oral antivirals (e.g., acyclovir, ganciclovir ophthalmic gel)

Acanthamoeba Keratitis

• A parasitic infection increasingly linked to contact lens use and exposure to contaminated water
• Presents as a red eye where initial bacterial cultures are negative - often misdiagnosed early
• Pathophysiology not fully understood; can be devastating if treatment is delayed
• Requires specific anti-amoebic therapy (e.g., PHMB, chlorhexidine eye drops)

Fungal Keratitis

• Consider in chronic ulcers or immunocompromised patients
• Common in agricultural settings (trauma with plant material)
• Treatment: topical natamycin or voriconazole

3. Orbital Cellulitis

Orbital cellulitis: proptosis, eyelid swelling, restricted eye movement - Tintinalli's Emergency Medicine

• Most common source: Extension from sinusitis (especially ethmoid sinus)
• Also from: trauma, hematogenous spread
• Peak age: ~12 years old
• Pathogens: S. pneumoniae, S. aureus, S. pyogenes, M. catarrhalis, anaerobes (Bacteroides, Fusobacterium), nontypeable H. influenzae

• Proptosis (bulging eye)
• Impaired or painful eye movements
• Decreased visual acuity
• Chemosis (swelling of the conjunctiva)
• Afferent pupillary defect

• First-line: cefuroxime (50 mg/kg IV q8h) or ampicillin-sulbactam (50 mg/kg IV q6h)
• Add clindamycin or metronidazole if anaerobes suspected
• Add vancomycin if MRSA suspected
• Total course: ~3 weeks (IV then oral)
• Ophthalmology + ENT co-management; surgery if abscess present

4. Endophthalmitis (Intraocular Infection)

Exogenous Endophthalmitis

• More common; pathogens enter via the ocular surface
• Main risk factors: Cataract surgery, intravitreal injections (e.g., for macular degeneration)
• Eye trauma is the leading cause in some countries
• Pathogens: Coagulase-negative staphylococci (most common), Bacillus cereus after trauma (causes fulminant rapid vision loss)
• Treatment: Intravitreal antibiotic injections (primary); vitrectomy for severe or refractory cases; systemic antibiotics generally not added except in fungal cases

Endogenous Endophthalmitis

• Pathogens reach the eye via bloodstream (bacteremia or fungemia)
• Fungal: Candida spp. most common - candidemia carries ~9% risk of chorioretinitis and ~1.6% progression to endophthalmitis
• Risk factors: central venous catheters, IV drug use, severe immunocompromise
• Also caused by molds (Aspergillus, Fusarium)
• Treatment: systemic antifungal therapy with voriconazole or fluconazole for at least 4-6 weeks (IDSA guidelines) + intravitreal injections

5. Posterior Segment Infections (Retinitis)

CMV Retinitis

• Occurs in immunocompromised patients (HIV/AIDS, post-transplant)
• Features: retinal hemorrhages, perivascular exudates, granular retinitis with minimal vitritis
• Treatment: Induction with IV ganciclovir 5 mg/kg q12h OR oral valganciclovir 900 mg q12h for 2-3 weeks, then maintenance valganciclovir 900 mg daily

Acute Retinal Necrosis (ARN) / Progressive Outer Retinal Necrosis (PORN)

• Caused by VZV or HSV; extremely rare but an ophthalmologic emergency
• Mechanism: vaso-occlusive angiitis of retinal and choroidal vessels
• Rapid irreversible vision loss possible
• Symptoms: sudden vision decline, photophobia, floaters, eye pain/redness
• Requires urgent systemic antivirals

Summary Table