Infective Keratitis
Infective keratitis, also known as infectious keratitis and microbial keratitis, refers to an infection of the cornea and is a potentially sight-threatening cause of red eye.
This updated UKMLA guide to infective keratitis covers causes, risk factors, symptoms, diagnosis and management. Common subtypes include bacterial keratitis, fungal keratitis, Acanthamoeba keratitis, and herpes simplex keratitis.
Causes and Risk Factors
Infective keratitis can be classified into: [Ref]
| Category | Subcategories | Specific organisms | Risk factors |
|---|---|---|---|
| Microbial keratitis (includes 3 subtypes) | Bacterial keratitis (most common) | Gram +ve
Gram -ve
|
|
| Fungal keratitis | Filamentous fungi: Fusarium spp., Aspergillus spp., and Curvularia spp.
Yeasts: Candida spp. |
Corneal injury, especially involving vegetative matter or objects contaminated with soil | |
| Parasitic keratitis | Acanthamoeba species |
|
|
| Viral keratitis | Herpes simplex virus
Varicella zoster virus |
HSV:
VZV:
|
|
Clinical Features
General / shared presentation: [Ref]
- Red, painful eye
- Reduced visual acuity or blurred vision
- Photophobia
- Foreign body sensation
- Ocular discharge
- Hypopyon (collection of WBCs / pus in the anterior chamber of the eye)
Contact lens use is an important risk factor, especially for bacterial and Acanthamoeba keratitis
Conjunctivitis vs keratitis
- Conjunctivitis is inflammation of the conjunctiva and is usually less serious, typically causing redness, irritation/grittiness and discharge, with normal vision and no significant pain or photophobia.
- Keratitis is inflammation/infection of the cornea and is potentially sight-threatening, suggested by eye pain, photophobia, reduced visual acuity, and contact lens use.
Complications
Key acute complications: [Ref]
- Corneal perforation
- Infectious spread → endophthalmitis
- Uveitis, scleritis
Chronic complications: [Ref]
- Corneal scarring
- Blurred vision and astigmatism
- Permanent vision loss
- Neurotrophic keratopathy (damaged sensory nerves innervating the cornea → loss of corneal sensation, reduced blink reflex, tear dysfunction)
Investigation and Diagnosis
ALL cases of corneal keratitis / ulcer are potentially sight-threatening emergencies, which warrant same-day referral to emergency eye service.
Work-up:
- Slit lamp examination +/- fluorescein staining to highlight surface defects (see below)
- Corneal scrapes for Gram stain, culture, and PCR (viral and acanthamoeba) – if the ulcer is >1 mm
Ocular appearance depending on the causative organism: [Ref]
| Causative organism | Typical ocular appearance |
|---|---|
| Gram +ve bacterial keratitis |
|
| Gram -ve bacterial keratitis (e.g. Pseudomonas) | Often more aggressive:
|
| Fungal keratitis |
|
| Acanthamoeba (parasitic) keratitis |
|
| Herpes simplex keratitis |
|
Management
ALL cases of infective corneal keratitis / ulcer are potentially sight-threatening emergencies, which warrant same-day referral to emergency eye service.
Disclaimer:
- There is no single universal UK guideline for the detailed management of all infective keratitis. Management varies by local ophthalmology/microbiology protocols
- For exam purposes, focus on recognising infective keratitis as an emergency and understanding the main drug classes used, rather than memorising exact organism-specific regimens listed below
The summary below is based on NHS GGC guidance and standard medical literature.
Only consider surgical interventions if medical therapies failed or the infection causes severe structural damage:
- 1st line surgical option: cyanoacrylate tissue adhesives or amniotic membrane transplants
- Last resort: therapeutic penetrating keratoplasty (corneal transplant)
Choice of medical therapies:
Bacterial Keratitis
Stop wearing contact lenses
Empirical antimicrobial therapy: [Ref]
| <1 mm | >1 mm |
Topical:
|
Topical:
Oral antibiotics to be considered by the corneal team in severe cases |
Admission criteria: [Ref]
- Ulcer >2mm
- Central ulcer
- Hypopyon present
- Impending corneal perforation
- Limbal / scleral involvement
- Likelihood of poor treatment compliance (e.g. lives alone)
Fungal Keratitis
Depends on the type of fungus: [Ref]
- Topical natamycin 5% for Filamentous fungi (e.g. Fusarium)
- Topical amphotericin B 0.15% or voriconazole 1% for yeasts (e.g. Candida)
Fungal keratitis generally has poor clinical outcomes because antifungal medications have poor penetration into the eye
Parasitic Keratitis (Acanthamoeba)
Acanthamoeba is highly resistant to therapy in its cyst form, so no single drug is effective [Ref]
- Primary regimen: polyhexamethylene biguanide 0.02% PLUS chlorhexidine 0.02%
- Drops are administered every hour for the first several days, and the overall treatment must be maintained for 6 to 12 months to prevent recurrence
Viral Keratitis
Herpes simplex keratitis (management depends on the layer of the cornea involved):
- Epithelial keratitis: topical OR oral antivirals (e.g. aciclovir, valaciclovir)
- Deeper (stromal and endothelial) keratitis: oral antivirals PLUS topical corticosteroids
- Long-term antiviral prophylaxis is also recommended to prevent recurrences
Herpes zoster keratitis:
- Oral antivirals (aciclovir / valaciclovir / famciclovir) to be started <72 hours of the onset