DEFINITIONS AND EPIDEMIOLOGY
Infection of the cornea (infectious keratitis) is potentially sight-threatening and requires prompt referral to an ophthalmologist. Infectious keratitis can be caused by a wide variety of pathogens with differing presentations. Prompt identification of the underlying etiology is imperative to guide the appropriate treatment choice and to prevent permanent vision loss, especially in children.
The cornea is a transparent, avascular structure that covers the anterior surface of the eye. At birth, the cornea measures 9.5–10.5 mm horizontally, growing to an adult size of 11–12 mm horizontally by age 2 years. The average newborn central corneal thickness is 960 µm, decreasing over time to an adult thickness of approximately 550 µm between ages 2 and 4 years.1 The corneal layers from anterior to posterior include epithelium, Bowman’s membrane, stroma, Descemet’s membrane, and endothelium. Infectious keratitis can involve one or more corneal layers, with varying clinical presentations. The anterior surface of the cornea is covered by the tear film, which contains components of the complement cascade, immunoglobulins, and cytokines.2 The tear film delivers nutrients to the avascular cornea and functions as a first-line defense against infections. Even distribution of the tear film over the corneal surface requires properly positioned eyelids and an intact blink reflex, which depends on intact corneal sensation. Inadequate eyelid closure and decreased corneal sensation predispose to infectious keratitis. These risk factors are of particular concern in the hospital setting since sedated patients may not completely close their eyelids, blink, or make adequate tears.
Vision loss can result from infectious keratitis due to obstruction of the visual axis from corneal scarring, or, in severe cases, from complications following corneal perforation. In children less than 7 years of age, several additional considerations make diagnosis and management of infectious keratitis more challenging. The developing cortical visual system requires symmetric and unobstructed visual input from each eye. Amblyopia can develop when corneal infection disrupts vision in one eye for any significant period of time, either by obstructing the visual axis or by causing significant refractive error. Prompt restoration of a clear visual axis with appropriate refractive correction can help prevent the development of amblyopia, but corneal scarring may prevent restoration of a clear visual axis. Furthermore, children may have difficulty expressing symptoms and cooperating with examinations, so they can present with more severe disease,3 further predisposing them to amblyopia. Even after appropriate diagnosis, treatment often requires extended courses of topical antibiotics, which may be difficult to administer.4 For these reasons, early diagnosis and intervention for infectious keratitis in children is particularly important.
The annual incidence of keratitis has been estimated at 11 in 100,000 in the United States and has increased significantly in recent decades with the growing popularity of contact lenses.5 For most underlying etiologies, no gender predilection has been identified. However, some studies ...