**2. Type and quality of donors used for PK and DALK**

Controversy exists regarding the donor corneal tissue quality used for each transplantation technique, especially DALK. When indicated for optical purposes, PK surgeons prefer transplanting donor cornea tissues with quality ranging from good to very good to excellent to provide adequate endothelial cells for a lifelong period. The acceptable conditions for PK donors are donor age varying from 1 to 96 years [9-16], endothelial cell density between 2000 and ≥ 3000 cells/mm2 [9, 10, 17, 18], death-to-preservation time between 45 minutes and 22.3 hours [11, 14, 15, 19], and storage time up to 14 days in cool-storage media and 4 weeks in organ culture [11-13].

In contrast to penetrating keratoplasty, donors with quality ranging from fair to excellent are employed for DALK [20, 21]. Furthermore, long-term preserved donor tissues completely devoid of cells are also transplanted [22-25]. One DALK study used donor cornea tissues with age between 12 and 72 years, graft rating from fair to excellent, endothelial cell density (ECD) between 1128 and 4255 cells/mm2 , death-to-preservation time up to 56 hours, and storage time up to 13 days in Optisol medium (-4°C) [20]. Another DALK study used donors with the following features: age between 28 and 88 years, ECD between 100 and 3300 cells/mm2 , and storage time up to 35 days in organ culture medium (31°C) [21]. Long-term preserved corneas with mean storage time between 2.7 and 9.6 months are also used for DALK by some surgeons [22-25]. Frequently, lyophilization or chemical agents are used to dehydrate corneas before cryopreservation [22-24]. However, it is possible to employ cryopreservation without dehy‐ dration before freezing as indicated by one study [25].

**1. Introduction**

78 Advances in Eye Surgery

eye banks to reevaluate their donor selection criteria.

outcomes, complications, and graft survival.

and ≥ 3000 cells/mm2

organ culture [11-13].

**2. Type and quality of donors used for PK and DALK**

Penetrating keratoplasty (PK) is a surgical technique in which the full thickness of the recipient cornea is replaced by donor tissue. Deep anterior lamellar keratoplasty (DALK) is intended to selectively replace the abnormal stroma while preserving the recipient's endothelium in place [1]. Therefore, DALK can eliminate the risk of endothelial graft rejection and has minimal detrimental effect on endothelial cell density [2]. Some investigators report that visual acuity and refractive error following DALK can be similar to those following PK [3-6]. Since the introduction of DALK, many surgeons have been accepting donor corneas with lower quality compared with PK. DALK does not rely on quality of the donor endothelium and requires less strict criteria for donor selection [7]. As a result, long-term preservation techniques are being revisited to increase the availability of donor corneas and subsequently alleviate constraints of availability, cost, storage, and transportation in many countries. This feature is imperative in increasing the availability of corneal grafts in regions where there is shortage of donor corneas [7]. The recent alterations in corneal transplantation techniques and consequently the type of donor cornea tissues employed for each technique may require corneal surgeons and

There is currently a paucity of evidence for setting an acceptable minimum donor conditions for corneal transplantation, especially for lamellar keratoplasty. According to Eye Bank Association of America standards for human corneal transplantation, minimal endothelial cell count limits, the upper and lower limit of donor age, time intervals from death, enucleation or excision to preservation are left to the discretion of the eye banks [8]. An understanding of the effect of donor variables including age, time interval from death to enucleation and preserva‐ tion, storage time, and endothelial cell density both on the quality of donor corneas and on posttransplantation outcomes helps to set eye banking standards. To establish the criteria, it is vital to find out the correlation between these donor parameters and the appropriateness of corneas for transplantation as well as between donor parameters and posttransplantation outcomes. This chapter presents an updated analysis on the type and quality of donor corneas used for PK and DALK, assesses the influence of donor and eye-bank factors on the quality of donor corneas, and furthermore determines whether any of these donor factors affect clinical

Controversy exists regarding the donor corneal tissue quality used for each transplantation technique, especially DALK. When indicated for optical purposes, PK surgeons prefer transplanting donor cornea tissues with quality ranging from good to very good to excellent to provide adequate endothelial cells for a lifelong period. The acceptable conditions for PK donors are donor age varying from 1 to 96 years [9-16], endothelial cell density between 2000

hours [11, 14, 15, 19], and storage time up to 14 days in cool-storage media and 4 weeks in

[9, 10, 17, 18], death-to-preservation time between 45 minutes and 22.3
