What are the characteristics and treatment of a peripheral bacterial corneal ulcer?

Characteristics and Treatment of Peripheral Bacterial Corneal Ulcer

Peripheral bacterial corneal ulcers are characterized by stromal infiltration with suppurative appearance at the corneal periphery, often with an epithelial defect, and require prompt treatment with topical fluoroquinolones or fortified antibiotics depending on severity.

Clinical Characteristics

Location and Appearance

• Located at the peripheral cornea (away from central 3mm zone)
• Crescent-shaped infiltration pattern following the limbus
• Epithelial defect with underlying stromal involvement
• Suppurative appearance with white-yellow infiltrate
• Distinct infiltrate margin that may show:
  • Suppuration
  • Necrosis
  • Soft or feathery edges
  • Crystalline appearance in some cases 1

Associated Findings

• Conjunctival injection/hyperemia
• Anterior chamber reaction (cells and flare)
• Possible hypopyon in severe cases
• Corneal thinning or melting may occur
• Neovascularization from adjacent limbus 1

Differential Features

• May be associated with systemic autoimmune conditions (rheumatoid arthritis)
• Can be triggered by bacterial conjunctivitis in predisposed individuals 2
• Must be distinguished from peripheral ulcerative keratitis (PUK) which has an immune-mediated etiology 3
• Different from fungal ulcers which typically have dry appearance, feathered edges, and satellite lesions 1

Diagnostic Approach

Slit Lamp Examination

1. Evaluate corneal epithelium for defects using fluorescein staining
2. Assess stromal involvement:
   • Depth of infiltrate
   • Degree of thinning
   • Presence of suppuration
   • Character of infiltrate margins 1
3. Check anterior chamber for inflammation and hypopyon
4. Examine adjacent conjunctiva and limbus for inflammation

Microbiological Testing

• For small, peripheral ulcers without stromal melting:

  • Cultures and stains are optional 1
  • Empiric therapy may be initiated without cultures

• For ulcers that are:

  • Large (≥2mm)
  • Associated with stromal melting
  • Chronic or unresponsive to treatment
  • Atypical in appearance
  • Multiple in number
  • Cultures and smears should be obtained prior to initiating antibiotics 1

Proper Culture Technique

1. Use topical anesthetic without preservatives (avoid tetracaine due to antimicrobial effect)
2. Obtain scrapings from advancing borders of the infected area using:
   • Heat-sterilized platinum spatula
   • Sterile blade
   • Jeweler's forceps 1
3. Inoculate directly onto appropriate culture media or place in transport media
4. Send for Gram and Giemsa staining 1

Treatment Algorithm

For Small Peripheral Bacterial Ulcers

1. First-line therapy: Topical fluoroquinolone monotherapy

   • Ciprofloxacin 0.3%
   • Ofloxacin 0.3%
   • Levofloxacin 1.5% 1
   • Apply every hour while awake initially, then taper based on clinical response

2. Dosing schedule:

   • Initial loading: Every 15 minutes for first 6 hours
   • First day: Every 30 minutes
   • Subsequent days: Every hour while awake until healing 4

For Severe or Central Bacterial Ulcers

1. Preferred therapy: Fortified antibiotics

   • Combination of fortified cefazolin (50mg/ml) and fortified gentamicin/tobramycin (14mg/ml) 5
   • Apply every 5-15 minutes as loading dose, then hourly 1

2. Add cycloplegic agents to:

   • Decrease synechiae formation
   • Reduce pain from anterior segment inflammation 1

3. Monitor closely for:

   • Clinical response
   • Development of corneal thinning/perforation
   • Anterior chamber reaction

Monitoring and Follow-up

Response Assessment

• Re-evaluate within 24-48 hours after initiating treatment
• Look for:
  • Decrease in infiltrate density
  • Reduction in anterior chamber inflammation
  • Re-epithelialization of the ulcer
  • Resolution of symptoms

Treatment Modification

• If no improvement after 48 hours:
  • Consider changing antibiotics based on culture results
  • Consider stopping antibiotics for 12-24 hours and reculturing 1
  • For deep stromal involvement, consider corneal biopsy

Complications to Monitor

• Corneal perforation
• Progressive corneal thinning
• Development of endophthalmitis (rare but serious)
• Corneal scarring affecting vision 6

Prevention Strategies

• Proper contact lens hygiene for lens wearers
• Prompt treatment of corneal abrasions with prophylactic antibiotics
• Management of predisposing ocular surface disease
• Patient education about signs and symptoms requiring urgent evaluation 1

Common Pitfalls and Caveats

1. Misdiagnosis: Bacterial and fungal keratitis can be difficult to distinguish clinically (correct in <70% of cases by specialists) 1

2. Delayed cultures: Obtaining cultures after starting antibiotics reduces yield; cultures should be taken before initiating treatment in severe cases

3. Inadequate treatment: Peripheral ulcers may seem less threatening but can progress rapidly with certain virulent organisms

4. Overlooking systemic disease: Peripheral ulcers may be associated with systemic autoimmune conditions requiring systemic evaluation 3

5. Inappropriate patching: Avoid patching eyes with contact lens-related corneal abrasions due to increased risk of bacterial keratitis 1