How to Combat Post-keratoplasty Infections Isn't Always Clear

Infection is one of the most dreaded complications after ocular surgery. Although it is considered rare, the rate of fungal infections after corneal transplantation is nonetheless increasing in the United States.

As detailed in a recent review paper, this uptick in fungal infections is primarily being seen following endothelial keratoplasty, mainly Descemet stripping endothelial keratoplasty (DSEK) and Descemet membrane endothelial keratoplasty rather than full-thickness or anterior lamellar keratoplasty.

There are a couple of reasons why this might be the case.

During tissue processing, endothelial keratoplasties are exposed to warmer temperatures for extended periods of time, an environment conducive to the growth of fungi. Moreover, the lamellar interface is a sequestered hypoxic location that can promote fungal growth.

A Troubling Trend

While this topic has been the subject of lively discussions in corneal circles for over 5 years, there is still no consensus on a solution.

Early detection of increased infection risk following transplantation can theoretically be done using cultures of the corneal donor rim obtained at the time of surgery. Rim cultures were routinely performed for bacterial and fungal species for decades, but that practice was abandoned by most surgeons because the concordance of positive rim cultures and actual infection was so low. Given the increase in fungal infections following endothelial keratoplasty, however, many surgeons have returned to performing rim cultures in these eyes, if only for fungal organisms.

A 2017 retrospective study analyzed over 3400 corneal transplants from 1996 to 2015. Investigators found positive rim cultures in 71 cases (2.1%) but infection in only four, of which three were in the DSEK eyes (the other was in a deep anterior lamellar keratoplasty). Among the DSEK eyes in this study, there were 26 positive rim cultures, meaning that over 10% developed an infection. All infections were with the same fungal organism as the rim culture.

I've attended several meetings where highly skilled, thoughtful, ethical corneal specialists have passionately argued both for and against obtaining fungal rim cultures on all endothelial keratoplasty surgeries.

Before deciding whether to obtain rim cultures, however, the critical question to ask is: What are you going to do if it comes back positive with no clinical evidence of infection? Are you going to treat prophylactically? A high percentage of positive rim cultures are false positives, rendering prophylactic treatment unnecessary while incurring additional costs and potential toxicity. On the other hand, early treatment prior to clinical signs and symptoms may prevent an overt infection.

The use of antifungal additives in the storage media to prevent infection is another important issue. Although many studies have looked at different concentrations of a variety of antifungals and their efficacy in killing organisms, effect on endothelial cell density, and associated cost, there is certainly no consensus on the best way to proceed here either.

At my institution, some surgeons are routinely obtaining fungal rim cultures, while others are not. Similarly, some surgeons use tissue from eye banks that provide antifungal medication in the storage media, while others do not. For my part, I agree with the conclusion of the review paper: Before we advocate for a change to standard procedures, larger-scale validation studies are needed.

Christopher J. Rapuano, MD, is a nationally and internationally recognized expert in corneal diseases, chief of the Wills Eye Hospital Cornea Service, and professor of ophthalmology at Sidney Kimmel Medical College at Thomas Jefferson University.

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Cite this: How Best to Combat Post-keratoplasty Infections Isn't Always Clear - Medscape - Nov 03, 2020.

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