TABLE 1

Common microbiologic causes of keratitis

EtiologyOrganismTypical clinical manifestationsMicrobiologic diagnosis notesTreatment
ViralHerpes simplex virus (HSV)Decreased visual acuity, loss of corneal sensation, scar formation; dendritic epithelial lesions upon slit lamp examination (8)PCR testing of corneal swab/scrapings is the preferred diagnostic method; direct immunofluorescence and viral culture may also be used (8)Antivirals (acyclovir, valacyclovir, ganciclovir); topical corticosteroids may be used for stromal or endothelial involvement (8)
AdenovirusPhotophobia, pruritus, tearing, burning, or foreign body sensation; examination may show a superficial punctate keratitis and hyperemia (9)PCR of conjunctival scraping of epithelial cells is preferred; direct immunofluorescence and viral culture may also be used (9)Usually self-limiting; symptomatic treatment with topical corticosteroids or antihistamines; cidofovir or topical alpha interferon can be used for refractory cases (9)
Varicella-zoster virus (VZV)Variety of syndromes, including herpes zoster ophthalmicus, conjunctivitis, and keratitis; dermatomal pain and erythematous macules that progress to pustules, which rupture and crust; slit lamp examination can reveal subepithelial infiltrates (10)PCR of corneal swab/scrapings is the preferred diagnostic method; direct immunofluorescence and viral culture may also be used (11)Acyclovir and topical or oral steroids are effective for keratitis or uveitis; intravenous acyclovir and laser intervention are recommended for acute retinal necrosis or progressive outer retinal necrosis (10)
BacterialPseudomonas aeruginosaCommonly associated with contact lens use; decreased visual acuity and corneal ulcers (12)Gram staining and bacterial culture of corneal scrapings (13)Systemic and topical antibiotics, such as ceftazidime (13), are used; there is no significant benefit of corticosteroids (12)
Staphylococcus aureusTypically associated with centrally located corneal ulcers; preexisting ocular surface disease is a risk factor (14)Gram stain and bacterial culture of corneal scrapingsTopical antibiotics, such as vancomycin, are used depending on antimicrobial susceptibility test results; therapeutic penetrating keratoplasty may be needed for refractory cases (14)
FungalFusarium speciesDecreased visual acuity, corneal ulcer, or abscess (15); typically follows trauma involving inoculation with vegetable matter or wood (16)Fungal smear and fungal culture of corneal scraping or contact lens solution (15)Topical natamycin, adjunctive oral voriconazole, or penetrating keratoplasty for corneal perforation (15, 16)
Aspergillus speciesTraumatic inoculation with vegetable matter, which may cause a corneal scar or epithelial defect (17)Fungal smear and fungal culture of corneal scraping or contact lens solution (18)Topical and/or oral voriconazole (17)
Candida speciesTypical host resides in temperate climates and has preexisting ocular surface disorder; may present with hypopyon (19)Fungal smear and fungal culture of corneal scraping or contact lens solution (19)Oral voriconazole for mild or moderate infections; addition of topical amphotericin B for severe infection (19)
Microsporidia (e.g., Vittaforma corneae, Encephalitozoon hellem) (20)Recurrent erythema, pain, photophobia, and decreased vision; usually affects contact lens wearers and those with HIV (20)Spores are seen upon conjunctival/corneal scrapings or biopsy; electron microscopy or PCR is required for definitive diagnosis and species identification (20)No known definitive medical treatment; options include topical 0.1% propamidine isethionate or systemic itraconazole; penetrating keratoplasty is useful for medically refractory cases (20)
Parasitic or protozoalAcanthamoeba speciesPain, photophobia, and increased lacrimation; usually affects contact lens wearers (1)Cysts and trophozoites are visualized with various stains, including the H&E and Papanicolaou stains; plate culture on nonnutrient agar overlain with bacteria or PCR (where available) is preferred for diagnosis (1)Topical chlorhexidine gluconate (6); penetrating keratoplasty is used for disease that spreads to the corneal stroma (1)