**5. Effect of donor and eye-bank variables on clinical outcomes, complications, and graft survivals following DALK**

DALK does not rely on donor endothelial cells and less strict criteria can be used for donor graft quality. Therefore, it increases the availability of donor tissues that do not require highquality endothelium to be appropriate for PK. Borderie et al [21] evaluated the effect of donor variables on the result of different anterior lamellar keratoplasty techniques in a heterogeneous group of corneal disorders with normal endothelium. The age of donor was the only factor which influenced visual rehabilitation postoperatively; visual acuity was significantly lower in recipients who received corneas from donors > 80 years [21]. Heindl et al [45] did not observe any significant association between donor storage time intervals and visual results one year following DALK. However, the use of low quality donors for DALK could cause epitheliumrelated complications more frequently, besides more edematous alterations of the graft necessitating a closer follow-up immediately after surgery. Feizi et al [20] observed that graft rating and preservation-to-surgery time had a significant correlation with the presence of graft stromal edema and epithelial defects on postoperative day 1 following DALK. Suture-related complications, graft rejection episodes, graft clarity, visual acuity, and refractive outcomes at the final follow-up examination were found to have no correlations with any donor or eyebank factors [20]. Therefore, low quality donors can provide good visual acuity and refractive outcomes with complication rates comparable to those achieved after the use of good quality donors following DALK.

The two main techniques for storing corneas are organ culture and hypothermia [46, 47]. Since lamellar corneal transplantation makes it possible to use acellular corneal tissue, long-term preservation methods have emerged as a means to provide a greater availability of corneal tissue to alleviate constraints of availability, cost, storage, and transportation in many coun‐ tries. The results of several studies indicate that cryopreserved corneal tissues can successfully substitute for fresh grafts in DALK using the big-bubble technique. Five studies concluded that long-term cryopreserved donors can provide similar visual results comparable to fresh corneal tissues following DALK [22, 23, 25, 48, 49]. Another advantage of long-term preser‐ vation of the cornea by lyophilization and chemical glycerin-dehydration is to eliminate cells such as epithelium, keratocytes, and antigen-presenting cells and create the acellular biological materials [22, 50]. As such, acellular corneal tissues may significantly reduce or even eliminate the incidence of graft rejection after lamellar keratoplasty [22, 23, 25]. Complications such as persistent epithelial defects, filamentary keratitis, and suture-related complications were more likely to occur when such a low quality graft was transplanted [25].
