Corneal ulcers
Corneal ulcers: Excerpt from Professional Guide to Diseases (Eighth Edition)
A major cause of blindness worldwide, ulcers produce corneal scarring or perforation. They occur in the central or marginal areas of the cornea, vary in shape and size, and may be singular or multiple. Marginal ulcers are the most common form. Prompt treatment (within hours of onset) can prevent visual impairment.
Causes
Corneal ulcers generally result from protozoan, bacterial, viral, or fungal infections. Common bacterial sources include Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus viridans, Streptococcus (Diplococcus) pneumoniae, and Moraxella liquefaciens; viral sources comprise herpes simplex type 1, variola, vaccinia, and varicella-zoster viruses; and common fungal sources are Candida, Fusarium, and Cephalosporium.
Other causes include trauma, exposure, reactions to bacterial infections, toxins, trichiasis, entropion, allergens, and wearing of contact lenses. (See What happens in corneal ulceration.) Tuberculoprotein causes a classic phlyctenular keratoconjunctivitis, vitamin A deficiency results in xerophthalmia, and fifth cranial nerve lesions lead to neurotropic ulcers.
Signs and symptoms
Typically, corneal ulceration begins with pain (aggravated by blinking) and photophobia, followed by increased tearing. Eventually, central corneal ulceration produces pronounced visual blurring. The eye may appear injected. If a bacterial ulcer is present, purulent discharge is possible.
Diagnosis
A history of trauma or use of contact lenses and flashlight examination that reveals irregular corneal surface suggest corneal ulcer. Exudate may be present on the cornea, and a hypopyon (accumulation of white cells in the anterior chamber) may appear as a white crescent moon that moves when the head is tilted.
Confirming diagnosis Fluorescein dye, instilled in the conjunctival sac, stains the outline of the ulcer and confirms the diagnosis.
Culture and sensitivity testing of corneal scrapings may identify the causative bacteria or fungus, and may indicate appropriate antibiotic or antifungal therapy.
Treatment
Prompt treatment is essential for all forms of corneal ulcer to prevent complications and permanent visual impairment. Treatment usually consists of systemic and topical broad-spectrum antibiotics until culture results identify the causative organism. The goals of treatment are to eliminate the underlying cause of the ulcer and to relieve pain:
❑ Fungi — topical instillation of natamycin for Fusarium, Cephalosporium, and Candida.
❑ Herpes simplex type 1 virus — topical application of trifluridine drops or vidarabine ointment. Corneal ulcers resulting from a viral infection often recur, requiring further treatment with trifluridine.
❑ Hypovitaminosis A — correction of dietary deficiency or GI malabsorption of vitamin A.
❑ Infection by P. aeruginosa — polymyxin B and gentamicin, administered topically and by subconjunctival injection, or carbenicillin and tobramycin I.V. Because this type of corneal ulcer spreads so rapidly, it can cause corneal perforation and loss of the eye within 48 hours. Immediate treatment and isolation of hospitalized patients are required.
Alert Treatment for a corneal ulcer due to bacterial infection should never include an eye patch because patching creates the dark, warm, moist environment ideal for bacterial growth.
❑ Neurotropic ulcers or exposure keratitis — frequent instillation of artificial tears or lubricating ointments and use of a plastic bubble eye shield.
❑ Varicella-zoster virus — topical sulfonamide ointment applied three to four times daily to prevent secondary infection. These lesions are unilateral, following the pathway of the fifth cranial nerve, and are typically quite painful. Give analgesics as ordered. Associated anterior uveitis requires cycloplegic eyedrops. Watch for signs of secondary glaucoma (transient vision loss and halos around lights).
Special considerations
❑ Keep the room darkened and orient the patient as necessary.
❑ Teach the patient how to properly clean and wear his contact lenses to prevent a recurrence.
Pictures
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
More About Cornea disorders
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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