A review of technological advances in the management of bacterial, fungal, viral, and <i>Acanthamoeba</i> keratitis

Microbial keratitis is a major cause of monocular blindness worldwide. Trauma and contact lens wear are major risk factors. Bacteria are a major cause, but fungi, viruses, and <i>Acanthamoeba</i> can also cause the disease. Therapeutic options are dwindling with the rise of antimicrobial resistance in all of these microbes, but especially bacteria. Infection with resistant strains results in worse clinical outcomes. New antimicrobial therapies are being developed but most have yet to be either used to treat ocular infections or become commercially available. For bacterial keratitis, antimicrobial peptides (AMPs) are a potential new option, as are bacteriophages and even bacteria that eat other bacteria or maggot secretions. For fungal keratitis, ocular natamycin, with oral ketoconazole or voriconazole treatments, offer improved outcomes for severe cases. For viral keratitis, AMPs again offer hope as new therapeutics, as do RNA interference and CRISPR-Cas systems. The recent release of a commercially available polyhexamethylene biguanide eye drop is a step forward, but new therapies that can kill both <i>Acanthamoeba</i> trophozoites and cysts are still needed. Beyond antibiotics, photoactivated chromophores for keratitis-corneal collagen cross-linking and photodynamic therapy have been successfully used. Therapies for large ulcers or scarring include corneal gluing, tissue scaffolds such as amniotic membrane or conjunctival flaps, and tissue replacement through penetrating or lamellar keratoplasty.