History
Patients with bacterial keratitis usually complain of rapid onset of pain, photophobia, and decreased vision. It is important to document a complete systemic and ocular history in these patients to identify any potential risk factors that would have made them susceptible to develop this infection, including the following:
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Contact lens wear (Note the type of lens, wearing time, and type of disinfection system.)
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Trauma (including previous corneal surgery)
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Use of contaminated ocular medications
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Decreased immunologic defenses
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Use of immunosuppressive agents such as steroid drops that may predispose to infection
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Aqueous tear deficiencies
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Recent corneal disease (herpetic keratitis, neurotrophic keratopathy)
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Structural alteration or malposition of the eyelids
Physical
External and biomicroscopic examination of these patients reveals some or all of the following features:
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Ulceration of the epithelium; corneal infiltrate with no significant tissue loss; dense, suppurative stromal inflammation with indistinct edges; stromal tissue loss; and surrounding stromal edema
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Anterior chamber reaction (cells and flare) with or without hypopyon
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Folds in the Descemet membrane
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Upper eyelid edema
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Posterior synechiae
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Surrounding corneal inflammation that is either focal or diffuse
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Conjunctival hyperemia
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Adherent mucopurulent exudate
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Endothelial inflammatory plaque
Causes
Any factor or agent that creates a breakdown of the corneal epithelium is a potential cause or risk factor for bacterial keratitis. Furthermore, exposure to some virulent bacteria that may penetrate intact epithelium (eg, Neisseria gonorrhoeae) also may result in bacterial keratitis.
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By far the most common cause of trauma to the corneal epithelium and the main risk factor for bacterial keratitis is the use of contact lenses, particularly extended-wear contact lenses. Of patients with bacterial keratitis, 19-42% are contact lens wearers. Incidence of bacterial keratitis secondary to use of extended-wear contact lenses is about 8,000 cases per year. The annual incidence of bacterial keratitis with daily-wear lenses is 3 cases per 10,000.
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Contaminated ocular medications, contact lens solutions, or contact lens cases [1]
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Decreased immunologic defenses secondary to malnutrition, alcoholism, and diabetes ( Moraxella)
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Aqueous tear deficiencies
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Recent corneal disease (including herpetic keratitis and secondary neurotrophic keratopathy)
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Structural alteration or malposition of the eyelids (including entropion with trichiasis and lagophthalmos)
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Chronic dacryocystitis
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Use of topical corticosteroids
Physical Examination
A thorough anterior-segment slit-lamp examination in patients with suspected or confirmed bacterial keratitis is essential and should include the following:
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Best corrected visual acuity
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Examination for epithelial defects (seen with fluorescein)
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Examination for corneal infiltrates (whitish opacities in the cornea)
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Examination for other corneal findings such as thinning or corneal edema
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Seidel examination for leak of aqueous humor through a perforated area of cornea, if suspicious
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Anterior chamber examination for cells, flare, and hypopyon
Complications
The most feared complication of this condition is thinning of the cornea, secondary descemetocele, and eventual perforation of the cornea that may result in endophthalmitis and loss of the eye.
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Human eye anatomy.
