Infectious keratitis: A review

Abstract

Globally, infectious keratitis is the fifth leading cause of blindness. The main predisposing factors include contact lens wear, ocular injury and ocular surface disease. Staphylococcus species, Pseudomonas aeruginosa, Fusarium species, Candida species and Acanthamoeba species are the most common causal organisms. Culture of corneal scrapes is the preferred initial test to identify the culprit organism. Polymerase chain reaction (PCR) tests and in vivo confocal microscopy can complement the diagnosis. Empiric therapy is typically commenced with fluoroquinolones, or fortified antibiotics for bacterial keratitis; topical natamycin for fungal keratitis; and polyhexamethylene biguanide or chlorhexidine for acanthamoeba keratitis. Herpes simplex keratitis is mainly diagnosed clinically; however, PCR can also be used to confirm the initial diagnosis and in atypical cases. Antivirals and topical corticosteroids are indicated depending on the corneal layer infected. Vision impairment, blindness and even loss of the eye can occur with a delay in diagnosis and inappropriate antimicrobial therapy.

Keywords: acanthamoeba keratitis; bacterial keratitis; fungal keratitis; infectious keratitis; viral keratitis.

FIGURE 1

Slit lamp image of a case of bacterial keratitis in a contact lens wearer with typical features; there is a central corneal infiltrate with an overlying epithelial defect and conjunctival hyperaemia

FIGURE 2

Bacterial keratitis in a failed corneal graft with a broken suture. The graft is oedematous and inferiorly a white infiltrate and larger epithelial defect can be seen within the graft. There is peripheral host vascularisation and conjunctival hyperaemia

FIGURE 3

Slit lamp image of a protruding cornea with bacterial keratitis. The patient has keratoconus complicated by corneal hydrops and then bacterial infection. Scattered infiltrates can be seen across most of the protuberant cornea and the conjunctiva is hyperaemic

FIGURE 4

(A) Dendritic ulcer in epithelial herpes simplex keratitis stained with fluorescein. (B) Stromal herpes simplex keratitis with lipid keratopathy and vascularisation. (C) Stromal herpes simplex keratitis with ulceration. (D) Herpes simplex keratouveitis with anterior chamber cells

FIGURE 5

Corneal ulcer and infiltrates in a case Candida keratitis; the signs are similar to those found in bacterial keratitis

FIGURE 6

Ring infiltrate in acanthamoeba keratitis

FIGURE 7

Advanced acanthamoeba keratitis, scattered stromal infiltrates with corneal vascularisation and conjunctival hyperaemia are noted

FIGURE 8

In vivo confocal microscopy of acanthamoeba keratitis