Keratitis is a medically significant inflammatory condition involving the corneal epithelium and stroma, typically triggered by infectious agents.
Its rapid onset, potential for visual compromise, and diagnostic complexity demand a thorough understanding of microbial etiology, host responses, and therapeutic interventions.
Globally, keratitis remains a leading cause of preventable visual disability, particularly in tropical and developing regions where ocular trauma and inadequate access to care are prevalent.
Etiological Spectrum: Microbes That Invade the Cornea
Keratitis may be infectious or non-infectious, though the former accounts for the majority of vision-threatening cases. Infectious keratitis is subdivided based on pathogen type:
Bacterial Keratitis: Commonly caused by Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pneumoniae. P. aeruginosa, often associated with contact lens misuse, exhibits rapid corneal degradation due to its proteolytic enzymes.
Fungal Keratitis: Frequently found in agricultural settings, Fusarium and Aspergillus species dominate. Fungi gain access through minor trauma with vegetative matter, and diagnosis is often delayed due to insidious presentation.
Viral Keratitis: Typically due to Simplex Virus type 1 (HSV-1). Recurrent episodes can lead to stromal scarring and neovascularization.
Acanthamoeba Keratitis: Linked primarily to poor contact lens hygiene, this protozoan infection may mimic viral or fungal keratitis and is often refractory to conventional therapy.
Clinical Presentation: Hallmarks of Corneal Infection
Symptoms include photophobia, conjunctival hyperemia, tearing, and reduced visual acuity. Examination may reveal epithelial defects, stromal infiltrates, hypopyon or ulceration. Slit-lamp biomicroscopy remains the standard in assessing corneal pathology.
According to Dr. Penny Asbell, an ophthalmologist, "Early recognition and microbiological work-up are pivotal, as delays in appropriate antimicrobial treatment can significantly affect outcomes."
Diagnosis: Beyond Visual Inspection
Corneal scrapings are essential for Gram staining, culture, and sensitivity testing. Confocal microscopy may assist in detecting fungal elements or Acanthamoeba cysts in ambiguous cases. Polymerase chain reaction (PCR) is increasingly employed to detect viral DNA in atypical presentations.
Treatment Approaches: Pathogen-Directed Therapy
Management of keratitis must be guided by microbial identification:
Bacterial: Empirical therapy often starts with fortified antibiotics such as vancomycin and tobramycin until culture results are available.
Fungal: Natamycin 5% is the first-line agent for filamentous fungi, with amphotericin B reserved for yeast infections. Systemic anti-fungals may be required in deeper or refractory cases.
Viral: HSV keratitis is managed with topical trifluridine or ganciclovir, alongside antivirals like acyclovir in recurrent or stromal involvement.
Acanthamoeba: Treated with polyhexamethylene biguanide (PHMB) and chlorhexidine, though long-term therapy is often necessary.
Prevention and Prognosis: Avoiding Long-Term Sequelae
Preventive strategies include strict adherence to contact lens hygiene, use of protective eye-wear in high-risk environments, and prompt management of ocular trauma. Prognosis depends heavily on early intervention; delayed or inappropriate treatment can result in corneal perforation or the need for transplantation.
A recent study emphasized contact lens–related microbial keratitis remains the most preventable cause of infectious corneal blindness in the developed world.
Keratitis represents a convergence of microbial pathology and clinical urgency. With pathogen-specific responses and evolving resistance profiles, precise diagnosis and aggressive intervention are paramount. As antimicrobial resistance and environmental exposure patterns shift globally, continuous vigilance and up-to-date clinical protocols remain indispensable for effective management.
