Keratitis, Infectious

Key Features

• 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

• 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

• 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 ...