New Prep for Donor Ocular Tissue Removes Microbes

November 1, 2011 (Orlando, Florida) — A small prospective study has demonstrated the value of a tissue preservation regimen that includes cryopreservation in rendering corneoscleral donor tissue free of viable contaminating microorganisms. If confirmed in larger-scale studies, the approach could be valuable in providing tissue for surgical use.

The research was presented as a poster here at the American Academy of Ophthalmology 2011 Annual Meeting.

"Cryopreservation enables long-term storage of donor ocular tissue; however, nothing has been written in the literature about the effect of cryopreservation on the sterility of such tissue. Our results show the feasibility of antibacterial preservation and cryopreservation in the sterilization of donor ocular tissue that previously tested positive for microorganisms," Tenley Bower, MD, from the College of Medicine, University of Saskatchewan, Saskatoon, Canada, told Medscape Medical News.

The prospective study used donor tissue submitted to the Lions Eye Bank in Manitoba and Ontario in 2009. Most (89%) of the globes were acquired within 12 hours of donor death. Average age at death was 69 years. Any globe that was determined to harbor viable microorganisms was eligible. The age, sex, and health of the donor were immaterial (except for ocular infections not resolved at the time of death).

The donor globes were used soon after acquisition; the average time from donor death to preservation was 14 hours.

The microbial load of the 28 corneoscleral rim specimens was ascertained by culturing tissue on Sabhi media, Chocolate agar, and thioglycolate broth for, respectively, growth of pathogenic fungi, fastidious bacteria such as Haemophilus influenza, and anaerobic bacteria. Samples were exposed to a commercial antibacterial solution, containing a formulation of polymyxin B, neomycin, gramicidin, and benzalkonium chloride, and then cryopreserved at –16 to –18 ^oF for 1 month. The tissues were then reassayed for viable microorganisms using the same 3 media.

Donor tissue (n = 34) was most commonly contaminated with coagulase-negative Staphylococcus (47% of samples) and Staphylococcus aureus (14%). Less common microorganisms included Staphylococcus epidermidis, Enterococcus, Corynebacterium spp, and Escherichia coli.

In striking contrast, every treated sample was completely free of viable microorganisms.

While more work needs to be done to confirm these results, they are very encouraging in terms of ensuring the sterility of donor ocular tissue, Dr. Bower said.

"Our technique is adequate to completely eliminate microbiological growth on donor corneoscleral tissue specimens. It may someday be possible to use this as a routine preparation of donor tissue," the researcher told Medscape Medical News.

That aim might prove to be a tough sell.

"Cryopreservation will likely never be a reliable method of sterilizing tissue, especially for a purpose such as this. Larger numbers of samples are definitely needed to bolster the researchers' case. Until then, to my mind, the idea has no merit," Herbert Kaufman, MD, emeritus professor of ophthalmology, pharmacology, and microbiology at Louisiana State Medical School, New Orleans, told Medscape Medical News.

Funding for the study was provided by the Lions Save Sight Foundation. Dr. Bower and Dr. Kaufman have disclosed no relevant financial relationships.

American Academy of Ophthalmology (AAO) 2011 Annual Meeting: Abstract PO367. Presented October 24, 2011.