**Abstract**

Infectious keratitis tops the list of diseases leading to visual impairment and corneal blindness. Corneal opacities, predominantly caused by infectious keratitis, are the fourth leading cause of blindness globally. In the developed countries, infectious keratitis is usually associated with contact lens wear, but in developing countries, it is commonly caused by trauma during agricultural work. The common causative organisms are bacteria, fungus, Acanthamoeba, and virus. Severe cases can progress rapidly and cause visual impairment or blindness that requires corneal transplantation, evisceration, or enucleation. The precise clinical diagnosis, accurate diagnostic tools, and timely appropriate management are important to reduce the morbidity associated with infectious keratitis. Despite the advancement of diagnostic tools and antimicrobial drugs, outcomes remain poor secondary to corneal melting, scarring, or perforation. Eye care strategies should focus on corneal ulcer prevention. This review addresses the epidemiology, diagnostic approach, clinical manifestations, risk factors, investigations, treatments, and the update of major clinical trials about common pathogens of infectious keratitis.

**Keywords:** infectious keratitis, corneal ulcer, corneal scar, blindness, visual impairment

### **1. Introduction**

Infectious keratitis tops the list of diseases leading to visual impairment and corneal blindness. Globally, it is approximated that 1.3 billion people live with visual impairment [1]. The major causes of corneal blindness included infectious keratitis, ocular trauma, trachoma, bullous keratopathy, corneal degenerations, and vitamin A deficiency [2]. Corneal opacities, predominantly caused by infectious keratitis, are the fourth leading cause of blindness globally [3]. Recent paper reported that 3.5% of global blindness could be attributed to corneal opacity [4]. According to the goal of the "Vision 2020: The Right to Sight," which was proposed by WHO, the prevention of avoidable corneal blindness should receive more awareness [5, 6].

Interestingly, the majority of visual impairment is avoidable [1]. Infectious keratitis accounts for 10% of avoidable visual impairment in the world's least-developed countries [3]. The number of people with avoidable visual loss has increased considerably because of population growth and aging. This trend will continue beyond

2020 [7] and will inevitably impact the eye care need in the near future. In the developed countries, infectious keratitis is usually associated with contact lens wear, but in developing countries, it is commonly caused by trauma during agricultural work [8–17]. Infectious keratitis is characterized by a corneal epithelial defect with underlying stromal inflammation caused by replicating microorganisms [14]. Acute eye pain and redness are the common presentation [14]. The common causative organisms are bacteria, fungus, Acanthamoeba, and virus [10, 17]. However, corneal infection involving more than one microorganisms such as bacteria and fungus is relatively uncommon [17] Microbial keratitis requires acute ophthalmic care and aggressive treatment to stop the disease progression and limit the extent of corneal scarring, which can cause loss of vision [14]. The precise clinical diagnosis, accurate diagnostic tools, and timely appropriate management are important to reduce the morbidity associated with infectious keratitis. This review addresses the epidemiology, diagnostic approach, clinical manifestations, risk factors, investigations, treatments, and the update of major clinical trials about common pathogens of infectious keratitis. The purpose of this review is to provide a concise and essential knowledge about common etiologic pathogens of infectious keratitis to improve understanding and reduce morbidity and visual loss due to this condition.
