OP4.3 | Infective Keratitis: Differential Diagnosis and Management — Summary & Reflection

KEY TAKEAWAYS

Infective keratitis (corneal ulcer) requires organism-specific treatment. The four major categories are:

Bacterial (Pseudomonas in contact-lens wearers, Staphylococcus/Streptococcus in trauma/surface disease): rapid onset, dense creamy infiltrate, hypopyon, mucopurulent discharge; Gram stain from scraping; treat with topical fluoroquinolones or fortified antibiotics.

Fungal (filamentous: Aspergillus, Fusarium — vegetative/agricultural trauma; yeast: Candida — immunocompromised): subacute, feathery/hyphate margins, satellite lesions, endothelial plaque, viscous hypopyon; KOH mount of scraping; treat with natamycin 5% (filamentous) or voriconazole; no steroids.

HSV dendritic keratitis: branching ulcer with terminal bulbs; stains with BOTH fluorescein and rose bengal; reduced corneal sensation; treat with topical aciclovir 3% ointment 5 times daily or ganciclovir 0.15% gel; never use steroids in active epithelial disease — causes conversion to geographic ulcer.

Acanthamoeba (contact-lens wearers + tap-water exposure): severe neuritic pain out of proportion; ring infiltrate; radial keratoneuritis (pathognomonic); Giemsa/calcofluor white staining shows cysts; culture on non-nutrient agar + E.coli; treat with PHMB 0.02% + chlorhexidine 0.02% for months.

Complications: stromal thinning → descemetocele (emergency) → perforation → endophthalmitis. Post-infective scar: keratoplasty after full resolution.

REFLECT

Reflect on the theme of this module: the treatment mismatch. In rural India, a farmer with fungal keratitis often presents to a primary care doctor who prescribes the 'standard antibiotic + steroid' combination empirically — and the fungal ulcer explodes, the eye perforates within a week, and a working adult loses his eye and his livelihood. As a future doctor, what changes in your practice will you make to ensure you take a proper history (including vegetative trauma) before prescribing for any corneal ulcer? How would you explain to a primary care colleague in a rural area why they should never add a steroid to any red eye with a white spot unless they have excluded HSV keratitis?