How should I treat a left‑eye fungal keratitis that has persisted after 7 days of topical tobramycin with only slight residual swelling and a non‑painful, non‑tender infiltrate?

Stop Tobramycin Immediately and Switch to Antifungal Therapy

You are treating a fungal infection with an antibiotic—tobramycin has no activity against fungi and must be discontinued immediately. The persistent infiltrate after 7 days of tobramycin strongly suggests this is fungal keratitis, not bacterial, and continuing inappropriate therapy risks corneal perforation and vision loss.

Critical First Steps

Discontinue tobramycin now and initiate topical antifungal therapy. The current presentation—a non-painful, non-tender infiltrate with slight swelling after failed antibiotic therapy—is classic for fungal keratitis that has been inadequately treated 1.

Immediate Management Algorithm

1. Start topical natamycin 5% hourly as first-line therapy

   • Natamycin is superior to voriconazole for filamentous fungal keratitis, improving visual acuity by approximately 2 Snellen lines and reducing perforation risk by 58% 2
   • If natamycin is unavailable, use topical voriconazole 1% hourly as second-line 3, 4

2. Obtain corneal scrapings immediately for:

   • KOH preparation and fungal staining
   • Fungal culture on appropriate media
   • This should have been done before starting any therapy 1

3. Examine for specific fungal features:

   • Feathered edges of the infiltrate
   • Satellite lesions
   • Endothelial plaque
   • Ring infiltrate pattern
   • These findings confirm fungal etiology 1, 4

Why This Case Failed Initial Treatment

The lack of pain is actually concerning—it suggests the infection may be progressing despite minimal symptoms, particularly if the patient was on any corticosteroids (which you should verify immediately). Fungal keratitis treated with antibiotics alone will inevitably worsen 1.

Critical Pitfall to Avoid

Do NOT add corticosteroids at this stage. The guidelines are explicit: corticosteroids in fungal keratitis increase the risk of requiring penetrating keratoplasty and lead to poor outcomes 1, 5, 1. Steroids should only be considered after:

• Fungal infection is definitively ruled out, OR
• After 2-3 days of documented improvement on antifungal therapy with pathogen identification 1

Monitoring and Escalation Plan

Re-examine within 48-72 hours to assess response. Look for:

• Reduced infiltrate density
• Sharper demarcation of infiltrate borders
• Decreased stromal edema
• Beginning epithelial healing
• Resolution of any endothelial plaque 5

If No Improvement After 10-14 Days of Intensive Topical Therapy:

Consider intrastromal voriconazole injection (50 µg/0.1 mL) circumferentially around the ulcer:

• Achieves 90.5% complete resolution in recalcitrant cases 6
• Most cases (66.7%) respond to a single injection 6
• Can be combined with intrastromal amphotericin B (0.01 mg/0.1 mL) for persistent cases, achieving 87.5% resolution 7

Surgical Intervention Thresholds:

Therapeutic penetrating keratoplasty is indicated if:

• Progressive corneal thinning despite medical therapy
• Impending or actual perforation
• Failure of medical therapy with worsening infiltrate 6, 4

Key Clinical Pearls

• Aspergillus is the most common organism in fungal keratitis (52.4% of cases) 6
• The mean time to complete epithelial closure with appropriate antifungal therapy is approximately 45 days—this is a marathon, not a sprint 7
• Topical therapy should not be tapered below 3-4 times daily even when improving, as subtherapeutic dosing promotes resistance 5
• Consider anterior segment OCT to assess infiltrate depth (mean depth ~257 µm in fungal cases) to guide therapy intensity 6

Bottom line: This patient needs antifungal therapy starting today, not continued antibiotics. Every day of delayed appropriate treatment increases the risk of perforation and permanent vision loss.