Classic and Atypical Presentations of Nocardia Keratitis: A Two-Case Report Highlighting Diagnostic Challenges.

Nocardia keratitis (NK) is an uncommon infectious keratitis that may present with characteristic or atypical corneal morphology. We report two patients with contrasting clinical appearances and diagnostic courses, highlighting the differing contribution of in vivo confocal microscopy (IVCM) and microbiological testing. A 19-year-old male farmer presented after suspected dust exposure with multiple superficial pinhead infiltrates arranged in a wreath-like pattern. Gram staining showed Gram-positive branching bacilli, and high-quality IVCM demonstrated fine hyperreflective branching structures at the ulcer margin. A 37-year-old male welder presented after ocular trauma with a sharply demarcated paracentral infiltrate. Initial Gram staining was negative, and an IVCM examination performed at a different site was technically limited and non-diagnostic; however, culture on chocolate agar grew Nocardia species after 3 days, and modified acid-fast staining confirmed partially acid-fast branching filaments. Both patients were diagnosed with NK and improved with amikacin-based topical therapy and sulfacetamide. These cases show that NK may have classic or atypical morphology and that a technically limited or inconclusive IVCM examination does not exclude the diagnosis. Corneal scraping, appropriate staining, and culture remain essential when NK is clinically possible.