Diagnosis: Bacterial Corneal Ulcer
Bacterial keratitis with corneal ulcer is an ophthalmic emergency that can result in permanent corneal scarring and irreversible vision loss. It is characterized by an epithelial defect with surrounding corneal stromal infiltrate. Early diagnosis is crucial in the prevention of permanent visual loss and to reduce structural damage to the cornea. Corneal ulceration can lead to a corneal opacification which contributes to loss of vision without prompt treatment. Risk factors for bacterial keratitis include use of contact lenses, ocular surface diseases like meibomian gland dysfunction blepharitis, corneal trauma, use of immunosuppressive medications and postocular surgery (ie following a corneal graft procedure). The most common risk factor for bacterial keratitis is contact lens wear.
The most common bacterial pathogens associated with corneal ulcers include pseudomonas, staph aureus, and strep species. Acanthamoeba is associated with swimming with contact lenses, so this history is important to obtain. It is clinically characterized by a ring infiltrate (see left image – image credit) and significant pain due to keratoneuritis. Sometimes, it can have a pseudodendrite appearance.
Corneal scrapings should be obtained to identify the causative organism. Gram and Giemsa stains and cultures should be performed. Chocolate, blood, sabouraud agar, and non-nutrient agar (with E. Coli overlay), and thioglycolate broth media should be used for cultures.
Corneal ulcers can also be noninfectious, associated with autoimmune etiologies such as Rheumatoid arthritis, Granulomatosis with polyangitis, Sjogren syndrom SLE, Polyarteritis nodosa, Scleroderma and others.
Topical broad spectrum antibiotic therapy such a fortified vancomycin and tobramycin drops should be initiated empirically until culture results are received. Bacterial keratitis can progress very quickly with complete corneal destruction occurring within 24-48 hours. If left untreated, they can lead to corneal perforation and loss of the eye. This is especially true for immunocompromised patients. Close follow up is important to monitor for improvement. Topical steroids can be started after a few days if clinically improving to assist with reducing associated inflammation.
In cases of acanthamoeba, there are a variety of treatment approaches but it will often include pool cleaner or polyhexamethylene biguanide (PHMB).
Non-healing ulcers can be treated with therapeutic penetrating keratoplasty (TPK), which involves the replacement of diseased cornea with a healthy donor corneal button.
References and Additional Resources:
1. Bartolomei A, et al. “Bacterial Keratitis.” American Academy of Ophthalmology EyeWiki. March 2022. Available at: https://eyewiki.aao.org/Bacterial_Keratitis.
2. Berfeld E, et al. “Acanthamoeba Keratitis.” American Academy of Ophthalmology EyeWiki. April 2022. Available at: https://eyewiki.aao.org/Acanthamoeba_Keratitis.
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