Bacterial keratitis

Overview

•Topical steroid eye drops - suppress local corneal immune response, leaving epithelium vulnerable to bacterial invasion even by low-virulence organisms

•Contact lens wear - especially extended-wear or overnight use; strongly associated with *Pseudomonas aeruginosa*

•Pre-existing ocular surface disease - associated with *Staphylococcus aureus* keratitis in non-contact lens wearers

🎯

Patient on steroid eye drops for uveitis or allergic eye disease who develops a painful red eye with a corneal infiltrate - think bacterial keratitis until proven otherwise. Steroids remove corneal immune surveillance, creating an open door for bacteria.

Presentation

•Painful red eye - severe, rapidly worsening over hours to days

•Photophobia - reflex ciliary spasm from anterior segment inflammation

•Reduced visual acuity - corneal opacification over the visual axis

•Watery or mucopurulent discharge

•Corneal infiltrate/ulcer - white/grey stromal opacity on slit-lamp

•Hypopyon - sterile white cell layer in anterior chamber; late and serious sign

Investigations

🏆 Gold standard

•slit-lamp examination - visualises infiltrate depth, size, and anterior chamber reaction (hypopyon, flare)

🥇 First-line

•fluorescein staining - irregular epithelial defect (contrast with dendritic pattern of HSV keratitis)

•corneal scraping for microscopy, culture and sensitivity - taken before starting antibiotics where possible

Management

•Stop contact lens wear immediately; same-day ophthalmology referral for any contact lens wearer or patient on topical steroids with corneal changes

🥇 First-line

•ciprofloxacin 0.3% eye drops or ofloxacin 0.3% eye drops - fluoroquinolones with broad-spectrum cover including *Pseudomonas*; intensive dosing initially (every 15-30 minutes)

•cyclopentolate (cycloplegic) - relieves painful ciliary spasm and prevents posterior synechiae

🥈 Second-line

•targeted topical antibiotics based on culture results - gentamicin or tobramycin for Gram-negatives; fortified vancomycin (Gram-positive) or ceftazidime (Gram-negative) for severe/non-responding cases

🥉 Third-line

•therapeutic penetrating keratoplasty - for perforation, refractory infection, or post-infectious scarring

⚠️

Topical steroids are contraindicated in active bacterial keratitis - they will worsen infection if used before adequate antimicrobial cover is established. Only an ophthalmologist should decide if and when to introduce them.