Tissue Processing and Preservation
Originally, donor corneal tissue was preserved within the whole globe, which was refrigerated at 4°C in a glass jar that served as a moisture chamber; this allowed tissue to be used up to 24–48 hours after donation. Extensive research on the importance of the endothelium for corneal allograft survival led to the development of McCarey-Kaufman (MK) medium, which extended the storage time to 4 days. Optisol GS (Bausch + Lomb, Bridgewater, NJ) is the most commonly used intermediate-term storage medium in the United States today, allowing the tissue to be stored for up to 11 days after death and in some circumstances up to 14 days. It contains chondroitin 2.5%, dextran 1%, ascorbic acid, and vitamin B12; it also includes gentamicin and streptomycin for broad-spectrum antibacterial coverage (Fig 15-1).
Table 15-3 Medical Criteria Contraindicating Donor-Cornea Use
The process of tissue recovery includes slit-lamp evaluation and an endothelial cell count at the eye bank before release for transplantation. The optimal time from death to recovery is less than 12 hours, but recovery is acceptable for up to 24 hours postmortem. After recovery, the donor tissue is stored at 4°C until use. Many eye banks prepare tissue for Descemet stripping automated endothelial keratoplasty (DSAEK) and DMEK once a cornea is deemed suitable for EK.
Table 15-4 Disease Transmission From Corneal Transplantation
Figure 15-1 Corneal tissue preserved in Optisol GS.
(Courtesy of Woodford S. Van Meter, MD.)
Most eye banks in Europe incubate donor corneal tissue in organ culture storage at 37°C. Organ culture allows tissue to be stored for up to 35 days but requires a culture at the end of the storage period to confirm sterility before the tissue is used. The organ culture system is more complex, costly, and labor-intensive than intermediate storage at 4°C, but the longer storage time is advantageous in places where the supply of donor corneas is limited.
Results of the Cornea Donor Study (CDS), a landmark study of eye bank–supplied corneal tissue, have greatly helped surgeons analyze and select donor tissue for their patients. The CDS, which completed enrollment in 2002 and conducted follow-up observations through 2012, evaluated the effect of donor age on graft survival in PK patients. Donors were grouped into cohorts age 10–64 years and age 65–75 years. At 5 years, the study showed no difference in the rate of graft survival between the 2 groups. However, at 10 years the rate of graft survival was slightly higher in patients receiving tissue from donors in the younger group than those receiving tissue from donors in the older group.
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Lass JH, Beck RW, Benetz BA, et al; Cornea Donor Study Investigator Group. Baseline factors related to endothelial cell loss following penetrating keratoplasty. Arch Ophthalmol. 2011; 129(9):1149–1154.
Malling JV. Eye banking: structure and function. In: Mannis MJ, Holland EJ, eds. Cornea. Vol 1. 4th ed. Philadelphia: Elsevier; 2017:283–286.
Sugar A, Gal RL, Kollman C, et al; Writing Committee for the Cornea Donor Study Research Group. Factors associated with corneal graft survival in the Cornea Donor Study. JAMA Ophthalmol. 2015;133(3):246–254.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.