Chronic infectious keratitis: A review of etiopathogenesis, clinical presentation and management challenges

Chronic infectious keratitis represents a distinct clinical entity characterized by indolent progression, diagnostic difficulty, and prolonged therapeutic courses. Unlike acute bacterial keratitis, chronic infections often present with subtle inflammatory signs, recurrent episodes, or poor response to empirical antimicrobial therapy. Among the most important causes are herpetic keratitis, acanthamoeba keratitis, Microsporidial stromal keratitis, and atypical (non-tuberculous) mycobacterial keratitis. Herpes simplex virus keratitis may manifest as recurrent epithelial disease or immune-mediated stromal inflammation resulting from viral latency and reactivation, frequently leading to corneal scarring and neurotrophic complications. Acanthamoeba keratitis, commonly associated with contact lens (CL) wear or water exposure, is characterized by severe pain disproportionate to clinical findings and the presence of cyst forms that confer significant treatment resistance. Microsporidial keratitis may present as either a self-limiting epithelial keratitis or a chronic stromal infection requiring surgical intervention, often masquerading as viral or fungal keratitis. Atypical mycobacterial keratitis typically follows corneal surgery or trauma and demonstrates a slow course with branching stromal infiltrates and minimal inflammation, frequently leading to delayed diagnosis. Other chronic infections such as Moraxella, Nocardia, Infectious Crystalline Keratopathy, Candida keratitis, and local adnexal factors causing chronic and recurrent bacterial infections have also been elaborated upon. These chronic pathogens share common challenges, including biofilm formation, intracellular persistence, cystic transformation, and steroid-modified presentations. Accurate diagnosis requires a multimodal approach incorporating smear, culture, polymerase chain reaction, and in vivo confocal microscopy. Management is organism-specific and often prolonged, sometimes necessitating therapeutic keratoplasty. Early recognition of chronic infectious keratitis is essential to prevent irreversible stromal damage and vision loss. This review is based on a literature search of PubMed, Google Scholar, and Cochrane databases using keywords such as 'infectious keratitis', 'herpes simplex viral keratitis', 'acanthamoeba keratitis', 'microsporidial keratitis', 'atypical mycobacterial keratitis', 'moraxella keratitis', 'infectious crystalline keratopathy', 'candida keratitis' and 'bacterial infections due to adnexal problems'.