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Fluoroquinolones
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CHARLOTTE, N.C.—By choosing to culture suspected infectious corneal ulcers, optometrists can maximize the advantage fluoroquinolones have provided in treating bacterial keratitis, said Ron Melton, OD, in practice here.
--- Ron Melton, OD
"Fluoroquinolones have revolutionized the treatment of corneal ulcers because many of the smaller, nonvision-threatening peripheral ulcers can be treated effectively without the encumberance of having to fortify non-standard concentrations of antibiotics," Melton said. "Fluoroquinolones are also very good agents to treat moderate to severe eye infections, in addition to corneal ulcers."
Pseudomonas is a very aggressive bacterial species and is the most common organism in contact lens-related ulcers. "The Pseudomonas corneal ulcer can evolve rapidly and lead to perforation of the eye in a short period of time if not treated properly," said Melton. Other common organisms causing bacterial corneal ulceration include Streptococcal, Staphylococcal, and Serratia species.
Melton acknowledged that the issue of culturing bacterial corneal ulcers is still unresolved. "Is it practical and cost-effective to culture bacterial corneal ulcers? That's been debated for many years but if you listen to the corneal specialists, the experts in microbial keratitis, they're going to tell you to culture the ulcer, be it peripheral, central, large or small," he said.
--- Randall Thomas, OD
Randall Thomas, OD, a private practitioner in Concord, N.C., said optometrists should culture all corneal ulcers for two reasons:
- It is the standard of care.
- If the bacterium resists initial therapy, the culture and sensitivities will guide the selection of alternate therapy.
"However, if it is a large, central ulcer, the patient should be referred to a fellowship-trained cornea/external disease subspecialist, because that eye is at risk for permanent scarring, possible perforation and possible loss," Thomas said.
In the case of a small, nonvision-threatening corneal ulcer, Thomas treats aggressively with a fluoroquinolone. "The therapy and frequency of administration will depend on the severity of the clinical situation," he said, "but for most patients you put a drop in every 15 to 30 minutes for the first several hours to sterilize the tissues."
Therapy can then be tapered to one drop every hour for a day or two. "Then, in this case, assuming things are getting better, I'd reduce that to one drop every two hours for a few days," said Melton. "Once you've neutralized the bacteria, the body's natural healing processes will come into play in an attempt to reestablish normal tissues."
Three topical fluoroquinolones are available; however, ciprofloxacin HCl (Ciloxan, Alcon) is the only one approved by the Food and Drug Administration for treating bacterial corneal ulcers.
Thomas also agreed with experts at the Wills Eye Hospital in Philadelphia who addressed concerns about bacterial resistance to a broad-spectrum antibiotic such as ciprofloxacin. "They note that the role of ciprofloxacin remains unresolved in treating corneal ulcers, but favor its use in treating small, nonvision-threatening ulcers, and using fortified broad-spectrum antibiotics for vision-threatening ulcers," he said.
Differential diagnosis:
Corneal ulcer vs. corneal infiltrate
- Corneal infiltrates are more common than true bacterial corneal ulcers. As a rule, corneal ulcers are more central, while corneal infiltrates are more peripheral. Also, with a corneal ulcer, the eye will be globally injected; with an infiltrate, the eye will likely be sectorially injected.
- In a corneal infiltrate, the underlying zone of infiltrate is usually larger than the smaller epithelial defect, if present. In a bacterial corneal ulcer, however, the defect is similar in size to the underlying stromal infiltration.
- Upon slit lamp microscopic examination of a corneal infiltrate, the iris details can be seen clearly. With a corneal ulcer, hazing and a decreased ability to visualize the underlying iris tissues occur. Also, small inflammatory white cells are often visible in the anterior chamber with infectious ulcers.