Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 7-09: Infectious Keratitis + Key Features Download Section PDF Listen +++ ++ Important categories of infectious keratitis include bacterial, herpetic, fungal, and amebic Bacterial keratitis Risk factors Contact lens wear—especially overnight wear Corneal trauma, including refractive surgery Commonly isolated pathogens Staphylococci, including methicillin-resistant Staphylococcus aureus (MRSA) Streptococci Pseudomonas aeruginosa Moraxella species Other gram-negative bacilli Herpes simplex keratitis An important cause of ocular morbidity The ability of the virus to colonize the trigeminal ganglion leads to recurrences that may be precipitated by fever, excessive exposure to sunlight, or immunodeficiency Herpetic corneal disease is typically unilateral but can occur bilaterally in the setting of atopy or immunocompromise Herpes zoster ophthalmicus Frequently involves the ophthalmic division of the trigeminal nerve Long-term complications Recurrent anterior segment inflammation Neurotrophic keratitis Posterior subcapsular cataract Optic neuropathy, cranial nerve palsies, acute retinal necrosis, and cerebral angiitis occur infrequently HIV infection is an important risk factor and increases the likelihood of complications Fungal keratitis Tends to occur after corneal injury involving plant material or in an agricultural setting, in eyes with chronic ocular surface disease, and in contact lens wearers Usually an indolent process Amebic keratitis Seen in contact lens wearers Severe pain with perineural and ring infiltrates in the corneal stroma + Clinical Findings Download Section PDF Listen +++ ++ Bacterial keratitis Cornea has an epithelial defect and an underlying opacity Hypopyon may be present Herpes simplex keratitis The dendritic (branching) corneal ulcer is the most characteristic manifestation of herpetic corneal disease More extensive ("geographic") ulcers also occur, particularly if topical corticosteroids have been used Stromal herpes simplex keratitis produces increasingly severe corneal opacity with each recurrence Herpes zoster ophthalmicus Malaise, fever, headache, and periorbital burning and itching may precede the eruption by a day or more The rash is initially vesicular, quickly becoming pustular and then crusting Involvement of the tip of the nose or the lid margins predicts involvement of the eye Ocular signs include conjunctivitis, keratitis, episcleritis, and anterior uveitis, often with elevated intraocular pressure Fungal keratitis May be an indolent process Corneal infiltrate may have feathery edges and multiple "satellite" lesions A hypopyon may be present Unlike bacterial keratitis, an epithelial defect may or may not be present Amebic keratitis Although severe pain with perineural and ring infiltrates in the corneal stroma is characteristic, earlier forms are identifiable with changes confined to the corneal epithelium + Diagnosis Download Section PDF Listen +++ ++ Bacterial keratitis For severe central ulcers, diagnostic scrapings can be sent for Gram stain and culture Herpes simplex keratitis These ulcers are most easily seen after instillation of fluorescein and examination with a cobalt blue light Herpes zoster ophthalmicus Diagnosis usually made on clinical grounds alone Direct fluorescent antibody staining of exudate from the base of any unroofed lesion among the grouped, tense, deep-seated vesicles is diagnostic Fungal keratitis Corneal scrapings should be cultured on media suitable for fungi Diagnosis is often delayed Amebic keratitis Diagnosis is facilitated by confocal microscopy and Giemsa staining of cornea smears Culture requires specialized media + Treatment Download Section PDF Listen +++ ++ Bacterial keratitis Topical fluoroquinolones, such as levofloxacin 0.5%, ofloxacin 0.3%, norfloxacin 0.3%, or ciprofloxacin 0.3%, are commonly used as first-line agents Apply compounded high-concentration topical antibiotic drops hourly day and night for at least the first 48 hours Fourth-generation fluoroquinolones (moxifloxacin 0.5% and gatifloxacin 0.3%) are also frequently used in this setting Although early adjunctive topical corticosteroid therapy may improve visual outcome, it should be prescribed only by an ophthalmologist Herpes simplex keratitis Resolution of corneal herpetic disease is hastened by treatment with topical antiviral agents (trifluridine drops, ganciclovir gel, acyclovir ointment [not available in the United States]) or oral antiviral agents such as acyclovir, 400–800 mg five times daily or valacyclovir 500–1000 mg three times daily for 7–14 days Topical antiviral agents may cause corneal toxicity after approximately 10–14 days of therapy and for that reason are not commonly used for chronic suppressive therapy Herpes zoster ophthalmicus High-dose oral acyclovir (800 mg five times a day), valacyclovir (1 g three times a day), or famciclovir (250–500 mg three times a day) started within 72 hours after the appearance of the rash reduces the incidence of ocular complications but not of postherpetic neuralgia Keratitis can be treated with topical antiviral such as ganciclovir 0.15% gel, 1 drop five times daily until healing has occurred and then one drop three times daily for 1 more week Anterior uveitis requires treatment with topical corticosteroids and cycloplegics Neurotrophic keratitis is an important cause of long-term morbidity Any patient with herpes zoster ophthalmicus and ocular symptoms or signs should be referred urgently to an ophthalmologist Fungal keratitis Natamycin 5% 1 gtt every 1–2 hours for 3–4 days, then 1 gtt six to eight times/day for 14–21 days (or amphotericin 0.1–0.5% or voriconazole 1%) are the most commonly used topical agents Systemic imidazoles may be helpful Corneal grafting is often required Amebic keratitis Intensive topical compounded biguanide (polyhexamethylene or chlorhexidine) is initiated immediately and long-term treatment is required Diamidine (propamidine or hexamidine) may be added Oral miltefozine FDA approved for the treatment of amebic keratitis However, indications and efficacy have yet to be established Patients should be monitored closely for systemic toxicity (vomiting, diarrhea, elevation of transaminases and kidney function studies) Corneal grafting to restore vision may be required after resolution of infection If there is scleral involvement systemic anti-inflammatory and immunosuppressant medication is helpful in controlling pain, but the prognosis is poor