Fig. 7.1
Principle of split cornea transplantation to use one donor cornea for two recipients. A single donor cornea can be split into two parts. The anterior part (including epithelium, its basement membrane, Bowman’s layer, and stroma) is transplanted using deep anterior lamellar keratoplasty (DALK) in corneal diseases affecting solely the anterior stroma and not the endothelium-Descemet’s membrane layer (e.g., keratoconus). The posterior part (endothelium-Descemet’s membrane layer) is grafted using Descemet’s membrane endothelial keratoplasty (DMEK) in corneal endothelial diseases (e.g., Fuchs’ endothelial dystrophy) without anterior stromal scarring (Modified from Refs. [52] and [53])
The split use of donor tissue is a relatively novel strategy in corneal transplantation. Vajpayee and coworkers described in a single case report the use of a single corneoscleral donor button in three patients by combining automated lamellar therapeutic keratoplasty for macular corneal dystrophy, DSAEK for pseudophakic bullous keratopathy, and limbal stem cell transplantation for limbal stem cell deficiency [59]. Recently, Lie and coworkers [60] as well as our group [52] reported the feasibility of split cornea transplantation by combining DALK and DMEK procedures for two recipients.
In an audit of our first 100 consecutive patients, split cornea transplantation could reduce the shortage of corneal tissue by 47 % [53]. In this initial series, a backup donor cornea was made available for every surgical intervention [53]. However, split donor cornea preparation (Fig. 7.2) could be performed successfully in all cases without inducing any significant central defects in the endothelium-Descemet’s membrane layer [53]. Similarly, all DMEK surgeries stripping the recipient Descemet’s membrane and inserting the endothelium-Descemet’s membrane graft (Fig. 7.3) were surgically successful [53]. In three out of the 50 eyes with anterior stromal disease (6 %), the DALK procedure (Fig. 7.4) had to be converted to PK, requiring a full-thickness corneal graft, owing to accidental macroperforation of the recipient Descemet’s membrane [53]. Therefore, a backup cornea was necessary, as otherwise, the surgery for the second patient would need to be canceled, resulting in problems with general anesthesia and patient convenience [53]. The follow-up revealed good visual and refractive outcomes with low complication rates and acceptable endothelial cell loss in our first 100 consecutive patients [53].
Fig. 7.2
Surgical technique of split donor cornea preparation. (a) Covering the corneoscleral button endothelial side up with saline and trypan blue solution. (b) Marking the central 8 mm by gentle trephine touch. (c) Incision of Descemet’s membrane peripheral to the marked circle with a razor blade. (d) Lifting the endothelium-Descemet’s membrane layer beyond the 8-mm mark using blunt anatomic forceps. (e) Setting three semicircular marks at the 8-mm margin using a 1-mm trephine. (f) Cutting through Descemet’s membrane using an 8-mm trephine. (g) Separation of the entire endothelium-Descemet’s membrane layer from the stroma underwater using blunt forceps. (h) Spontaneous formation of an endothelium-Descemet’s membrane roll with endothelial side outward transferred into culture medium for subsequent Descemet’s membrane endothelial keratoplasty (DMEK). (i) Circular, full-thickness trephination of the remaining anterior donor lamella using an 8.25-mm trephine for completing deep anterior lamellar keratoplasty (DALK) (Modified from Ref. [52])
Fig. 7.3
Surgical technique of Descemet’s membrane endothelial keratoplasty (DMEK). (a) Preparation of a 3-mm clear corneal tunnel at the 12-o’clock position. (b) Centripetal stripping of Descemet’s membrane using a Price hook. (c) Complete removal of the central 9-mm Descemet’s membrane. (d) Transfer of the donor endothelium-Descemet’s membrane graft obtained from split donor cornea preparation (see Fig. 7.2) into a conventional lens injector cartridge with endothelial side outward. (e) Injection of the graft into the anterior chamber. (f) Rotation of the graft for 90°. (g) Unfolding of the graft by an air-bubble injection on top of the graft. (h) Complete filling of the anterior chamber with air pressing the graft endothelial side down against the host corneal stroma. (i) Reduction of the air to approximately one fifth of the anterior chamber volume or complete anterior chamber air fill is left (Modified from Refs. [51] and [52])
Fig. 7.4
Surgical technique of deep anterior lamellar keratoplasty (DALK). (a) Marking the center of the recipient corneal surface with a surgical claw. (b) Circular, partial-thickness trephination with an intended depth of 90 % of the preoperative pachymetry using an 8-mm trephine. (c) Inserting a 30-gauge needle bevel down at the peripheral trephination and advancing it centripetally just above Descemet’s membrane. (d) Injection of a big air-bubble, resulting in a white, semiopaque disk to separate Descemet’s membrane from the stroma. (e) Injection of a small air-bubble into the anterior chamber, becoming visible at the periphery of the big bubble formation. (f) Cutting out the central stromal tissue using Katzin scissors. (g) Evidence of bare Descemet’s membrane without defects by the small air-bubble moving centrally in the anterior chamber. (h) Transfer of the anterior donor lamella obtained from split donor cornea preparation (see Fig. 7.2) into the recipient bed. (i) Fixation with a 16-bite double-running diagonal cross-stitch suture (Modified from Ref [52])
In Lie’s series, a total of 124 transplantations, i.e., 69 DMEK and 55 DALK procedures, could be performed out of a pool of 73 donor corneas, so that a total of 51 donor buttons (41 %) could be saved [60].
However, a recent retrospective audit of 1,141 consecutive donor corneas at our department revealed that only 15 % of corneal grafts could be performed as split cornea transplantation, resulting in 96 donor corneas being saved (8 %) [58]. The reason for this is that indications and referrals for DMEK exceed those for DALK by far (714 vs 100, respectively), at least at our department [58]. This asymmetric distribution suggests the need for scheduling DMEK and DALK recipients even more controlled.
Most recently, the Melles group published the hemi-DMEK technique splitting one endothelial graft into two half-moon-shaped grafts for two recipients [61, 62]. Since hemi-DMEK seems to provide visual outcomes similar to those in standard DMEK [62], hemi-DMEK is a promising method for increasing the pool of endothelial graft tissue, although severe doubts remain about long-term endothelial cell counts after this approach.
In summary, due to the ongoing revolution of corneal transplantation toward lamellar keratoplasty techniques, the split use of donor corneal tissue may become a standard approach to save corneal tissue and to reduce transplantation cost in the future.
7.4 Tissue Storage for DALK and DMEK Surgery
Split cornea transplantation raises the demands on the organization and daily work in the eye banks. Firstly, microbial contamination must be avoided. Therefore, the culture media with the donor cornea tissue and its residues should be examined microbiologically before and after each surgery owing to a presumably increased risk of contamination. Secondly, sophisticated logistics of quick patient allocation is crucial. Special precautions have to be taken to precisely track the use of tissue parts, even during busy operating room days, and, in particular, to ensure that human leukocyte antigen-matched donor tissue reaches the planned recipient.
Our initial concept of performing the DMEK procedure for the patient with corneal endothelial disease immediately after completing the DALK procedure for the patient with anterior stromal disease on the same surgery day led to increasing logistical difficulties in the clinical routine. Therefore, we have changed our surgical planning concept [53, 56]. Depending on the availability of the patients, either the DALK procedure is performed first and the posterior donor lenticule is stored to complete the subsequent DMEK procedure within 7 days or the DMEK procedure is performed first and the anterior donor lenticule is stored to complete the subsequent DALK procedure within 7 days [56]. This simplifies the logistics of patient allocation and makes split cornea transplantation more feasible in the clinical routine.
Indeed, longer storage of the anterior donor lenticule without endothelium before actual use in DALK surgery could cause more edematous alterations of the graft and loss of stromal keratocytes [57] that potentially could persist and thereby degrade vision and increase complications after lamellar keratoplasty. In an experimental study using light microscopy (Fig. 7.5) and electron microscopy (Fig. 7.6), corneal epithelium and stroma revealed significantly more edematous alterations after Descemet’s stripping than full-thickness corneas, with a marked increase from 1 to 3 culture weeks and marked anterior keratocyte loss within 3 culture weeks [57]. However, the 1-year outcomes (visual acuity, endothelial cell loss, central corneal thickness, and complication rate) after DALK using split donor tissue stored up to 1 week (Table 7.1) were well within the 1-year results reported by several groups for DALK using nonstored tissue [56]. Furthermore, longer storage of the posterior donor lenticule before actual use in DMEK surgery could be associated with a higher endothelial cell loss [57] that potentially could persist, thereby degrading vision and increasing complications after posterior lamellar keratoplasty. An experimental study on graft alterations after Descemet’s stripping revealed a linear decrease of the endothelial cell count of posterior lenticules within 4 culture weeks, showing a mean loss of 128 cells/mm2 per week [57]. Light (Fig. 7.5) and electron microscopy (Fig. 7.6) showed an intact and viable endothelium up to 3 culture weeks in split and non-split buttons [57]. In the clinical setting, the 1-year outcomes (visual acuity, endothelial cell loss, central corneal thickness, and complication rate) after DMEK using split donor tissue stored up to 1 week (Table 7.1) were well within the 1-year results reported by several groups for DMEK using nonstored tissue [56]. Therefore, these data support the possible safety of anterior and posterior donor tissue stored in organ culture up to 1 week after splitting for the use in DALK and DMEK surgery, respectively.
Fig. 7.5
Histopathologic graft alterations after Descemet’s stripping. Histopathology of split (a, b, d, e) and full-thickness (c, f) donor corneas after one (a–c) and three (d–f) additional weeks of organ culture showing more epithelial and stromal edema after Descemet’s stripping with a marked loss of keratocytes in the anterior stroma at 3 culture weeks and Descemet’s membrane with intact and viable endothelium up to 3 culture weeks without significant differences between stripped and non-stripped buttons (hematoxylin-eosin, original magnification × 200) (Modified from Ref. [57])
Fig. 7.6
Ultrastructural graft alterations after Descemet’s stripping. Transmission electron microscopy of split (a–c and g–i) and full-thickness (d–f and j–l) donor corneas after one (a–f) and three (g–l) additional weeks of organ culture showing more epithelial (a, d, g, j) and stromal (b, e, h, k) edema after Descemet’s stripping and Descemet’s membrane with intact and viable endothelium (c, f, i, l) up to 3 culture weeks without significant differences between stripped and non-stripped buttons (scale bar = 2.5 μm) (Modified from Ref. [57])
Table 7.1
One-year outcomes after split cornea transplantation combining deep anterior lamellar keratoplasty (DALK) and Descemet’s membrane endothelial keratoplasty (DMEK) in 220 eyes in dependence of the storage time after Descemet’s stripping
DALK using anterior donor lamellas with storage time after splitting | DMEK using posterior donor lamellas with storage time after splitting | |||||||
|---|---|---|---|---|---|---|---|---|
<1 h | 1–24 h | 25 h–3 days | 4–7 days | <1 h | 1–24 h | 25 h–3 days | 4–7 days | |
(n = 47) | (n = 21) | (n = 22) | (n = 20) | (n = 63) | (n = 17) | (n = 16) | (n = 14) | |
BSCVA (logMAR) | 0.18 ± 0.09 | 0.20 ± 0.06 | 0.18 ± 0.07 | 0.18 ± 0.09 | 0.09 ± 0.08 | 0.14 ± 0.14 | 0.13 ± 0.09 | 0.05 ± 0.07 |
Mean ± SD (range) | (0.0–0.4) | (0.1–0.4) | (0.0–0.3) | (0.0–0.4) | (−0.1–0.3) | (−0.1–0.3) | (0.0–0.3) | (−0.1–0.1) |
Spherical equivalent (D) | −1.5 ± 1.3 | −2.5 ± 1.1 | −1.2 ± 0.8 | −1.1 ± 0.9 | 0.8 ± 1.3 | 1.1 ± 1.3 | 1.3 ± 0.9 | 0.4 ± 0.6 |
Mean ± SD (range) | (−4.5–0.0) | (−5.0– − 0.5) | (−3.3–0.0) | (−3.5–0.0) | (−2.8–4.5) | (−2.5–4.3) | (−0.5–3.0) | (−0.5–1.5) |
Refractive astigmatism (D) | 1.2 ± 0.9 | 1.4 ± 0.7 | 1.0 ± 0.5 | 1.1 ± 0,4 | 0.6 ± 0.4 | 0.7 ± 0.7 | 0.5 ± 0.5 | 0.6 ± 0.4 |
Mean ± SD (range) | (0.5–3.5) | (0.5–3.0) | (0.0–2.0) | (0.5–2.0) | (0.0–1.5) | (0.0–2.5) | (0.0–1.5) | (0.0–1.5) |
Endothelial cell density (cells/mm2) | 1979 ± 133 | 2002 ± 61 | 2032 ± 49 | 2007 ± 116 | 1489 ± 192 | 1535 ± 238 | 1498 ± 197
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