What is Bacterial Keratitis?
Bacterial keratitis is a bacterial infection of the cornea that presents with pain, redness, blurred vision, photophobia, discharge, corneal infiltrates, ulcerations, and anterior chamber inflammation—a sight-threatening emergency requiring immediate ophthalmologic evaluation and treatment. 1
Definition and Clinical Significance
Bacterial keratitis is an infection of the cornea caused by bacteria that has the potential to cause permanent visual loss or blindness if not promptly diagnosed and treated. 1 The disease can progress extremely rapidly, with complete corneal destruction occurring within 24-48 hours when caused by virulent organisms, making it a true ophthalmic emergency. 1
Why Contact Lens Wearers Are at Highest Risk
Contact lens use is the single largest risk factor for bacterial keratitis in the United States, with extended wear contact lenses carrying dramatically higher risk than daily wear. 1
Specific Risk Stratification for Contact Lens Wearers:
- Extended wear: 20 per 10,000 wearers per year develop microbial keratitis 1
- Daily wear: 1-2 per 10,000 wearers per year develop microbial keratitis 1
- Daily disposable lenses: Lowest complication rate among all contact lens types 1
High-Risk Contact Lens Behaviors:
- Overnight wear (including orthokeratology) 1
- Inadequate disinfection or "topping off" solutions 1
- Rinsing contact lens cases with tap water 1
- Swimming, hot tub use, or showering while wearing lenses 1
- Overwear beyond FDA-approved replacement schedules 1
- Poor hand hygiene 1
Common Causative Organisms
The most common bacteria causing keratitis in contact lens wearers is Pseudomonas aeruginosa, followed by staphylococcal species. 1, 2
Organism Distribution:
- Gram-positive: Staphylococcus species (including coagulase-negative staphylococci and S. aureus), Streptococcus pneumoniae 1
- Gram-negative: Pseudomonas aeruginosa (most common gram-negative organism), Serratia marcescens 1, 2
- Polymicrobial infections: Occur in 43% of culture-positive cases 1
Geographic Variations:
- United States: Contact lens wear is the primary risk factor 1
- Southeast Asia and South India: Trauma is the primary risk factor 1
- Southern United States: Higher rates of gram-negative organisms compared to northern regions 1
Clinical Presentation
Patients present with the following constellation of symptoms and signs:
- Pain (often severe) 1
- Redness 1
- Blurred vision 1
- Photophobia 1
- Discharge 1
- Corneal infiltrates and ulcerations 1
- Anterior chamber inflammation 1
Natural History and Complications
Untreated or inadequately treated bacterial keratitis leads to corneal scarring, perforation, endophthalmitis, and potential loss of the eye. 1
Vision-Threatening Outcomes:
- Corneal opacification and irregularity causing permanent visual disability 1
- Central or paracentral infections carry the highest risk of substantial visual loss even with successful eradication 1
- Corneal perforation requiring emergency surgical intervention 1
- Progression to endophthalmitis with potential loss of the eye 1
Management Principles
Diagnosis and management require the clinical training and experience of an ophthalmologist, with corneal specialists preferred for severe or refractory cases. 1
When to Refer Immediately:
- Any suspected bacterial keratitis in a contact lens wearer 1
- Severe or vision-threatening keratitis 1
- Central or paracentral corneal involvement 1
- Refractory to initial treatment 1
Treatment Setting:
- Outpatient management: Appropriate for most cases with reliable patients 1
- Hospitalization indicated when: Severe or vision-threatening disease, compliance concerns, severe pain, or inability to self-administer drops due to age/disability 1
Antibiotic Therapy:
Broad-spectrum topical antibiotics remain the primary treatment, with empirical therapy based on Gram stain findings until culture results are available. 3, 4
- Most effective regimens (based on healing time): Vancomycin + ceftazidime, moxifloxacin monotherapy, or cefazolin + tobramycin 3
- Fluoroquinolone resistance: Increasing resistance of MRSA and Pseudomonas aeruginosa to fluoroquinolones documented from 2005-2015 1
- Corneal specialists: More likely to obtain cultures and prescribe fortified antibiotics for severe ulcers 1
Critical Patient Education Points
Contact lens wearers must understand that bacterial keratitis can cause permanent blindness and requires strict adherence to lens hygiene protocols. 1
Prevention Strategies:
- Never rinse lenses or cases with tap water 1, 5
- Use only sterile, commercially prepared contact lens solutions 5
- Replace lenses according to FDA-approved schedules 1
- Remove lenses before swimming, showering, or hot tub use 1
- Consider switching to daily disposable lenses after an episode of bacterial keratitis 1
Resuming Contact Lens Wear:
After bacterial keratitis, the risks and timing of resuming contact lens wear must be discussed, with reassessment of lens choice, fit, and mode of wear—strongly considering daily disposable lenses which have lower complication rates. 1
Global Burden
The WHO recognizes bacterial keratitis as a "silent epidemic" and a major cause of corneal blindness worldwide. 1