The success of any transplantation procedure depends on the availability and quality of corneal tissue. For that, the cornea surgeon is thankful for the outstanding work of eye banks nationally and internationally.
Eye Banking and Donor Selection
Before reliable storage or preservation methods were available, it was imperative that corneas be transplanted immediately from donor to recipient. The McCarey-Kaufman tissue transport medium, which was developed in the early 1970s, significantly reduced endothelial cell attrition, allowing corneal buttons to be safely transplanted after being stored for up to 4 days at 4°C. Improvements in storage media over the past 2 decades have extended the viable storage period to as long as 2 weeks, not only increasing the availability of donor corneas but also allowing the surgery to be performed on a less exigent basis. The most commonly used preservation medium in the United States today is Optisol-GS (Bausch + Lomb, Irvine, CA), which includes such components as 2.5% chondroitin sulfate, 1% dextran, ascorbic acid, vitamin B12, adenosine triphosphate precursors, and the antibiotics gentamicin and streptomycin.
Organ culture storage techniques are commonly practiced in Europe and have the potential to improve the quality of donor tissue in the future. Organ culture allows a longer storage time and sterility control of the medium, which is optimal for more remote locations. Its disadvantages include increased complexity and cost, as well as a thick, opaque cornea at the time of surgical transplantation.
Most eye banks in the United States prepare the corneal tissue for EK. Overall, 67,590 donors were provided by eye banks domestically and internationally in 2011; of these, 15,650 were prepared for EK using a microkeratome, laser, or hand dissection.
In the United States, not all eye banks are members of the Eye Bank Association of America (EBAA), but all eye banks must comply with US Food and Drug Administration regulatory requirements (Current Good Tissue Practices) implemented in 2005 to ensure the safety of human cells, tissue, and cellularand tissue-based products.
Criteria Contraindicating Donor Cornea Use
The EBAA has developed extensive criteria for screening donor corneas before distribution to avoid transmissible infections and other conditions. Contraindications include
death of unknown cause with likelihood of other exclusion criteria
congenital rubella
Reye syndrome within the past 3 months
active viral encephalitis of unknown origin or progressive encephalopathy (eg, subacute sclerosing panencephalitis, progressive multifocal leukoencephalopathy)
active bacterial or viral encephalitis
active bacterial or fungal endocarditis
suspected rabies or history of being bitten, within the past 6 months, by an animal suspected to be infected with rabies
Down syndrome (exclusion criterion for PK and ALK)
intrinsic eye disease
retinoblastoma
malignant tumor of the anterior ocular segment or known adenocarcinoma in the eye (primary or metastatic origin)
active ocular or intraocular inflammation: conjunctivitis, keratitis, scleritis, iritis, uveitis, vitreitis, choroiditis, or retinitis
congenital or acquired disorders of the eye that would preclude a successful outcome for the intended use (eg, a central donor corneal scar for an intended PK, keratoconus, keratoglobus)
leukemias
active disseminated lymphomas
high-risk behavior or incarceration in prison
prior refractive corneal surgery, such as radial keratotomy, photorefractive keratectomy, laser in situ keratomileusis (LASIK), and lamellar inserts, with the exception that previous laser refractive surgery may not disqualify a donor’s tissue for use in EK
negative test for anti-HIV-1 and anti-HIV-2 (or combination test), and nonreactive for hepatitis B surface antigen (HBsAg) and anti-HCV antibody
Corneas from patients with a history of intraocular surgery (cataract, intraocular lens [IOL] implantation, or glaucoma filtering surgery) may be accepted if endothelial adequacy is documented by specular microscopy and meets the local eye bank’s written standards; corneas from patients with prior refractive surgery as noted above may be used for EK if cleared by the eye bank’s medical director. Diseases known or suspected to be transmitted via corneal transplantation are listed in Table 15-2.
Table 15-2
Even with these standards, the ultimate responsibility for accepting donor tissue rests with the surgeon. Other factors to consider include the following:
slit-lamp appearance of donor tissue
specular microscopy data (generally, endothelial cell counts <2000 cells/mm2 are not used) death-to-preservation time (the optimal range is <12–18 hours)
tissue storage time before keratoplasty donor age
Most surgeons do not use corneas from donors younger than 24 months for PK, as they are extremely flaccid and can result in high corneal astigmatism and myopia postoperatively, but such corneas may be useful for EK. Age limits for donors who provide tissue for transplantation are up to the individual surgeon.
For various reasons, including the potential decline in suitable donor tissue because of widespread refractive surgery, the EBAA and the National Eye Institute sponsored the Cornea Donor Study in patients undergoing PK. The study completed enrollment in 2002, and follow-up has been extended from 5 to 10 years. The 1100 patients, aged 40–80 years, had endothelial dysfunction as an indication for the first graft in the study eye and were randomized to receive tissue from donors aged 10–64 or 65–75 years. The primary endpoint is graft failure. At the 5-year follow-up, the study showed no difference in transplant outcome between the 2 groups. In addition, neither the method of retrieval, processing factors, timing of donor cornea use, nor ABO incompatibility had an effect on graft survival. In a subset of 567 patients, preoperative and postoperative endothelial cell density (ECD) was followed. Larger grafts, younger donor age, and female donors were associated with higher ECD over 5 years, but the significance of this finding is unclear.
As for DSEK, in a large series from 1 center, no relationship was observed between postoperative donor endothelial cell survival and preoperative cell counts, donor storage time, use of precut tissue prepared by the eye bank, or donor tissue size.
Eye Bank Association of America (EBAA). Statistical Report on Eye Banking Activity for 2011. Washington, DC: EBAA; 2011. 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.
Sugar J, Montoya M, Dontchev M, et al; Cornea Donor Study Investigator Group. Donor risk factors for graft failure in the Cornea Donor Study. Cornea. 2009;28(9):981–985.
Terry MA, Li J, Goshe J, Davis-Boozer D. Endothelial keratoplasty: the relationship between donor tissue size and donor endothelial survival. Ophthalmology. 2011;118(10):1944–1949.