Utilize experts for complex cases of infectious keratitis

According to several sources, infectious keratitis is the fifth leading cause of blindness in the world.

In the United States, it is further down the list, with just more than 70,000 new cases of vision-threatening infectious keratitis diagnosed each year. With about 18,000 ophthalmologists in America, that means if divided evenly, each of us would see only four to six high-risk infectious keratitis cases each year. Many mild cases that are not vision threatening are treated empirically with a commercial prescription topical fluoroquinolone with rapid resolution. More central and severe cases have a less rosy prognosis, and in one review from the United Kingdom, just more than 50% required hospitalization and 16% required surgery, with 9% resulting in corneal perforation and 1.4% in enucleation or evisceration. A useful rule of thumb is the 1-2-3 rule. If there are greater than 1+ cells in the anterior chamber, the corneal infiltrate is larger than 2 mm or the infiltrate is within 3 mm of the center of the cornea, laboratory investigation and treatment with fortified antibiotics are indicated.

Most infectious keratitis cases in the U.S. are caused by bacteria, usually Staphylococcus, Streptococcus pneumoniae and Pseudomonas aeruginosa, but depending on the part of the country, fungi including Candida, Aspergillus and Fusarium are the cause in 5% to 20% of cases. In the contact lens wearer, Acanthamoeba is in the differential diagnosis, and herpes is always part of the infectious keratitis differential diagnosis as it is a great masquerader.

One important question is: What laboratory investigation is appropriate? In the mild non-sight-threatening peripheral case, none is indicated. When indicated, the traditional approach has utilized Gram and Giemsa staining for a rapid insight into the probable offending organism followed by cultures on appropriate media. Today, transport media and the use of multiplex strip PCR tests are replacing this approach, and modern PCR testing is more sensitive, specific and versatile in its ability to diagnose herpes simplex, fungi and Acanthamoeba as the cause of an infection. In rare cases such as Acanthamoeba, confocal microscopy is useful. Every practice environment will have a different level of access to each of these tests, and the ophthalmologist who chooses to care for these patients must work with their local laboratories to establish a pattern of practice. Many eye care professionals prefer to refer vision-threatening infectious keratitis to a corneal specialist for treatment.

First-line topical therapy with a prescription fluoroquinolone is readily available to every physician and patient in America. Off-label treatment with more frequent application of the topical eye drop at home by the patient or family is appropriate along with daily follow-up eye examinations until improvement is noted. For more severe bacterial infections, fortified antibiotics containing tobramycin and vancomycin are often prescribed. Accessing these fortified antibiotics can take time and effort, and many ophthalmologists are finding it convenient to keep a bottle of Fortisite with 1.5% tobramycin and 5% vancomycin from ImprimisRx on hand.

Some clinicians utilize topical steroids to reduce corneal scarring and opacity in centrally located infectious keratitis, but treatment with antimicrobial agents alone for the first 48 to 72 hours is wise, along with ruling out fungi as the cause where topical steroids are contraindicated. There is an art to treating sight-threatening infectious keratitis, and while there are some evidence-based principles, timely referral to an expert who treats these patients regularly for eyes that do not respond rapidly to treatment or progress despite treatment is prudent. Many of the useful treatments for complex cases require compounded agents that are not easily accessed, and advanced diagnostic tests such as confocal microscopy are usually only available in tertiary referral centers.

• References:
• Cabrera-Aguas M, et al. Clin Exp Ophthalmol. 2022;doi:10.1111/ceo.14113.
• Ting DSJ, et al. Front Med (Lausanne). 2021;doi:10.3389/fmed.2021.715118.

• For more information:
• Richard L. Lindstrom, MD, can be reached at rllindstrom@mneye.com.

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Sources/Disclosures

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Source:
Expert Submission

Disclosures:
Lindstrom reports having dis­closures for Harrow, ImprimisRx, Minnesota Eye Consultants and Unifeye Vision Partners.

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