Infectious
keratitis is a major global cause of
visual impairment and
blindness, often affecting marginalized populations. Proper diagnosis of the causative organism is critical, and although culture remains the prevailing diagnostic tool, newer techniques such as in vivo confocal microscopy are helpful for diagnosing fungus and Acanthamoeba. Next-generation sequencing holds the potential for early and accurate diagnosis even for organisms that are difficult to culture by conventional methods. Topical
antibiotics remain the best treatment for bacterial
keratitis, and a recent review found all commonly prescribed topical
antibiotics to be equally effective. However, outcomes remain poor secondary to corneal melting,
scarring, and perforation. Adjuvant
therapies aimed at reducing the immune response associated with
keratitis include topical
corticosteroids. The large, randomized, controlled
Steroids for Corneal
Ulcers Trial found that although
steroids provided no significant improvement overall, they did seem beneficial for
ulcers that were central, deep or large, non-Nocardia, or classically invasive Pseudomonas aeruginosa; for patients with low baseline vision; and when started early after the initiation of
antibiotics. Fungal
ulcers often have worse clinical outcomes than bacterial
ulcers, with no new treatments since the 1960s when topical
natamycin was introduced. The randomized controlled Mycotic
Ulcer Treatment Trial (MUTT) I showed a benefit of topical
natamycin over topical
voriconazole for fungal
ulcers, particularly among those caused by Fusarium. MUTT II showed that oral
voriconazole did not improve outcomes overall, although there may have been some effect among Fusarium
ulcers. Given an increase in nonserious adverse events, the authors concluded that they could not recommend oral
voriconazole. Viral
keratitis differs from bacterial and fungal cases in that it is often recurrent and is common in developed countries. The Herpetic
Eye Disease Study (HEDS) I showed a significant benefit of topical
corticosteroids and oral
acyclovir for stromal
keratitis. HEDS II showed that oral
acyclovir decreased the recurrence of any type of herpes simplex virus
keratitis by approximately half. Future strategies to reduce the morbidity associated with infectious
keratitis are likely to be multidimensional, with adjuvant
therapies aimed at modifying the immune response to
infection holding the greatest potential to improve clinical outcomes.