Therapeutic interventions for microbial keratitis

Abstract

Corneal infections by bacterial, viral, fungal or parasitic organisms are most commonly treated with topical agents. Unfortunately, due to a lack of evidence-based recommendations, prescribing behaviour can often be influenced by drug availability and prescriber preference. To address this gap and provide a sound evidence-base upon which to inform clinical decisions, a series of related studies were conducted investigating therapeutic interventions for microbial keratitis. A prospective observational study was conducted reviewing the clinical records of patients with microbial keratitis over a six month period. Bacterial keratitis (79% related to contact-lens use) presented most commonly. Associations were observed between herpes simplex keratitis and; Maori ethnicity, asthma, cardiovascular disease and long-term corticosteroid use. Further investigations into these associations are warranted and in particular, research is required on the effect of corticosteroid inhalers and topical applications on the ocular surface with regards to herpetic reactivation. Two systematic reviews were performed investigating the most appropriate topical ocular antibiotics and antifungals in patients with keratitis. The review of antibiotics revealed that treatment success, time to cure and serious complications of infection were comparable among all treatments. There was no difference in risk of corneal perforation with any antibiotics. Fluoroquinolones reduced risk of ocular discomfort and chemical conjunctivitis compared with aminoglycoside/cephalosporin, while fortified tobramycin/cefazolin was three times more likely to cause ocular discomfort. The review of antifungal treatment suggested that voriconazole was almost twice as likely to result in therapeutic keratoplasty compared with natamycin. Final visual acuity was significantly better with natamycin compared with voriconazole. A randomised controlled trial was conducted comparing a non-tapered course of prednisolone acetate 1.0% with placebo in patients with bacterial keratitis. No significant difference was noted in any of the study outcomes. However, patients using prednisolone experienced more epiphora on day three and worse visual acuity on day 14. The results of this RCT study, whilst ultimately underpowered due to patient recruitment issues, however, still contribute to the growing body of evidence regarding use of topical corticosteroids in bacterial keratitis. These aforementioned, inter-related, studies provide key evidence-based information for clinicians treating microbial keratitis, while also identifying particular areas requiring further research.