December 2018

CORNEA

Research highlight
Endothelial keratoplasty donor rim evaluation


by Maxine Lipner EyeWorld Senior Contributing Writer


Interface infiltrate after Descemet’s stripping endothelial keratoplasty
Source: Shahzad Mian, MD

 

Considering infection rates in preserved tissue

Some practitioners may harbor concerns that the longer tissue is preserved prior to endothelial keratoplasty, the more apt infections are to bloom. However, recent results indicate otherwise, according to Shahzad Mian, MD, professor of ophthalmology and visual sciences, Kellogg Eye Center, University of Michigan, Ann Arbor. A study1 that honed in on cultures performed at 0 to 7 days as well as at 8 to 14 days showed that the time of storage did not have an impact on the rate of positivity of donor rim cultures, Dr. Mian reported.
This investigation was an outgrowth of the Cornea Preservation Time Study in which investigators looked at the effect of expanding the donor pool by keeping tissue longer, he noted.2 “Historically, the medium that tissue is stored in in the United States is approved for use for 14 days, but most surgeons use the tissue within 7 and don’t go beyond that,” Dr. Mian said, adding that these initial results showed that tissue preserved for up to 12 days was equivalent in outcomes to tissue preserved for the shorter period.

Monitoring infection rate

In this study, investigators wanted to examine whether there were any differences in the rate of infection with longer preservation. Included in this trial were 784 patients for whom donor rim cultures had been obtained in the original investigation in which 1,330 were enrolled. They found that the rate of culture positivity for fungus was 1.9%, Dr. Mian said. When it came to bacteria, the overall rate was lower at 1.3% of positive rim cultures, mostly for the Propionibacterium species. “When we looked at the data in terms of whether length of preservation impacted positivity of donor rim cultures, we did not notice any difference in either group,” Dr. Mian said.
Just because the rim culture in some cases came back positive, it did not mean that infections developed. “For the infection rate, we saw there was one case in the 0- to 7-day group and two in the 8- to 14-day group, which gave us an overall percentage of 0.23%,” Dr. Mian said, adding that if the rim culture is positive, the infection rate was at 7%. “If someone has a positive rim culture, it does increase the risk of infection.”
Investigators also found a higher rate of culture positivity depending upon where the tissue was prepared. In cases where this was done by the practitioner, the rate of a positive rim culture was greater. “We think it’s because the longer the tissue is kept warm, the higher the risk of infection because the fluid where the tissue is preserved likely has contaminants,” Dr. Mian said. “If a surgeon is preparing it, this takes longer compared to eye banks where they process more and have become more efficient at doing this.” However, in most cases, the contaminants don’t amount to any significant clinical levels, Dr. Mian stressed.

Practical perspective

He views the results clinically as indicating that the overall risk of infection after endothelial keratoplasty is low regardless of time of storage. “If you have positive rim cultures, you need to pay more attention to determine if patients are developing any signs of infection,” he said, adding that some have proposed prophylactically treating them with antifungal medications since there are no preventative agents against this in the medium. However, with data lacking to prove the effectiveness, there is no clear consensus. “We can’t make a recommendation at this point based on our data,” Dr. Mian said.
When looking at “mate cultures” in the fellow eye, investigators did not find that because one eye had a positive rim culture, the other one was positive or that the risk of actual infection was higher. Still, if an infection occurs after a corneal transplant and the eye bank notifies the surgeon who transplanted the fellow cornea, the surgeon as well as the recipient can be on the alert for possible infections.
Dr. Mian hopes that practitioners come away from the study cognizant of the fact that endothelial keratoplasty has excellent clinical outcomes with low risk of failure. He also pointed out that clinicians should keep in mind that it’s safe to use tissue that has been stored for 11 or 12 days since the overall risk of infection is low. “We need to be cautious about infections—especially fungal infections,” he said. In addition, there is still value in doing rim cultures since this alerts practitioners of the possibility of a clinical infection ultimately emerging.
Overall, while Dr. Mian views the likelihood of infection with endothelial keratoplasty as low, he thinks there may be room for improvement. “I think the next step is to figure out whether there is a role for supplementation of antifungal agents within the medium to reduce risk of infection,” Dr. Mian said.

References

1. Mian SI, et al. Incidence and outcomes of positive donor rim cultures and infections in the Cornea Preservation Time Study. Cornea. 2018;37:1102–1109.
2. Lass JH, et al. Corneal endothelial cell loss 3 years after successful Descemet stripping automated endothelial keratoplasty in the Cornea Preservation Time Study: a randomized clinical trial. JAMA Ophthalmol. 2017;135:1394–1400.

Editors’ note: Dr. Mian has no financial interests related to his comments.

Contact information

Mian: smian@med.umich.edu

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