AKT · Ophthalmology/Cornea & ant. segment

Microbial keratitis (bacterial)

Infective corneal ulcer (Staph, Strep, Pseudomonas — contact-lens-related)

Overview

A sight-threatening infection of the corneal stroma (corneal ulcer). Strongly associated with contact-lens wear (especially overnight); Pseudomonas causes rapid, aggressive ulcers. Presents as a painful red eye with a white corneal infiltrate ± hypopyon. An ophthalmic emergency — scrape, intensive topical antibiotics, NO steroids/lenses.

Recognise

Painful red eye, photophobia, watering, reduced vision and discharge
White/grey corneal infiltrate or ulcer with an overlying epithelial defect (stains with fluorescein) ± HYPOPYON
Contact-lens wear (especially extended-wear/poor hygiene), trauma, or ocular surface disease

Red flags

Any contact-lens wearer with a red painful eye → assume microbial keratitis until excluded — same-day referral
Hypopyon, enlarging infiltrate, or central ulcer → urgent ophthalmology (perforation/scarring risk)

Differentials & how to tell them apart

Corneal abrasionepithelial defect WITHOUT a stromal infiltrate

HSV keratitisdendritic ulcer, reduced corneal sensation; steroids are dangerous

Acanthamoeba keratitiscontact-lens wearer with pain out of proportion to signs, ring infiltrate, water exposure

Marginal keratitisperipheral immune infiltrate with a clear gap from the limbus, associated with blepharitis — less aggressive

Microbial keratitis — corneal infiltrate with a hypopyon
Imrankabirhossain / CC BY-SA 4.0 — Wikimedia Commons

Investigations

Slit-lamp exam; corneal SCRAPE for Gram stain, culture and sensitivities BEFORE starting antibiotics where possible.

Management

Urgent referral + intensive topical fluoroquinolone after corneal scrape

1Same-day ophthalmology. Corneal scrape for microscopy/culture, then intensive topical broad-spectrum antibiotic (hourly fluoroquinolone, or fortified antibiotics for severe/central ulcers). Stop lens wear.Gate: Do NOT prescribe topical steroids or start antibiotics in primary care that could compromise the corneal scrape — refer; treat any contact-lens-related red painful eye as keratitis
2Adjust to culture results; cycloplegia for comfort; consider admission for hourly drops. Corneal perforation → glue/graft.

Intensive topical fluoroquinolone (e.g. ofloxacin/levofloxacin) — hourly, day and night, initially — first-line empirical

Fortified topical antibiotics (cefuroxime + gentamicin) — specialist, for severe/central ulcers

Cycloplegic — for pain/ciliary spasm

STOP contact lens wear; avoid topical steroids — steroids worsen untreated infection (esp. fungal/acanthamoeba/HSV)

Key points

Contact lenses + painful red eye + white corneal spot = microbial keratitis until proven otherwise. Hypopyon means a severe anterior-chamber reaction. Steroids and lenses are out.

Monitor & prognosis

Daily review until improving; watch for thinning/perforation.

Good if treated early; central scarring can permanently reduce vision.

Source: College of Optometrists CMG; RCOphth