Mycotic Keratitis, a State-of-the-Art Review

Microbial corneal diseases are a serious ocular infection and the major cause of ocular morbidity and blindness in the world. The outcomes of fungal keratitis are unfavorable due to the protracted course of the condition and the diversity of respective clinical presentations. Trauma, contact lens wear, foreign material, and prior corneal surgery, may make the most background for permitting invasion by exogenous fungi by injecting the fungal conidia directly in the corneal stroma. Other risk factors consist of blocked naso-lacrimal duct, and ocular surface disease. More than 105 species of fungi, such as Aspergillus spp., Fusarium spp., Candida spp., Rhizopus, Mucor, and other fungi have been identified as the etiological agents of fungal keratitis. The first step of diagnosis begins with clinical suspicion, followed by corneal scrapings or biopsy for direct smear and culture confirming the etiological agent. Slit lamp biomicroscope is used for careful examination of the infected eye and pictorial documents like the ulcer size, site, depth, extent of infiltration, abscess formation, and any perforation are evaluated. Direct smears are prepared by potassium hydroxide wet mount, or Gram's staining. To identify the isolates, a lactophenol cotton blue wet mount is prepared, and diagnosis is based on morphology of the culture media and details of microscopic examination. The results are highly specific but have suboptimal sensitivity varying in different studies. Molecular assays are valuable for the diagnosis of fungal keratitis in patients. Various advantages and limitations are reported for such methods. Overall, PCR is a sensitive and promising tool for the diagnosis of fungal keratitis but the expertise required and the lack of sophisticated facilities renders it inferior to the smear techniques in routine laboratory procedures and is not recommended accordingly. Rapid diagnosis and proper treatment are essential for fungal keratitis, and many patients require several months of therapy until the infiltrate is resolved and epithelial stroma are healed. Patients not responsive to antifungal therapy usually require corneal transplantation.