Ординатура / Офтальмология / Английские материалы / Corneal Endothelial Transplant (DSAEK, DMEK & DLEK)_John_2010

Figure 30-5: Pre-cut donor tissue with markings in trephine punch stage. In this instance, a Weck system is used as its Teflon stage is white, allowing the markings to be clearly visualized. The three bed diameter marks are seen close to the limbus indicating the predissected area. The trephination should be carried out within the arcs. A backwards “S” can also be seen inferiorly, indicating that the endothelial surface is facing the viewer. The centering mark can be seen overlying the center of the stage. Compare this to the diagram in Figure 30-3.

counts, and characteristics. It is also important to note the bed diameter as this is the maximum diameter of the prepared DSEK graft. The surgeon will use all of this information to confirm the health of the tissue and to determine whether the donor tissue is of appropriate size for the desired graft (Figures 30-3 and 30-4).

Removing the donor corneoscleral tissue from the transport container should reveal the markings in Figure 30-5. In the paracentral area, there are three arcs which indicate the extent of the anterior cap generated by the ALTK system (Moria S.A., Antony, France) (See also Chapter 12, Artificial Anterior Chambers). These arcs can be used to help guide centration during donor punching. There is also a centering dot for the same purpose. The surgeon should however, visually confirm that the dot is centered in the donor cornea. Finally, there is an “S” mark which helps with confirming the stromal side of the donor corneal disk (“S” is seen when viewed with the stromal side proximal to the viewer; “Z” (Editorial Note: “reversed –S”) is seen when viewed with the endothelial side proximal to the viewer).

[Editorial Note: In this method Gentian Violet is introduced into the anterior chamber (See also Chapter 32, Use of Dyes in DSAEK and DLEK). Recent evidence suggests that such use of markings with a marking pen can result in endothelial cell loss].

Cutting the Pre-cut Tissue

When determining the graft size to transplant, the surgeon must not only take into account the host dimensions, but he must also take into account the bed diameter of the precut tissue. This is listed in the documentation and is indicated visually on the tissue by the three arcs. The donor punching should occur within these arcs, as they describe the maximum extent of the pre-cut area. Cutting the tissue outside of the bed diameter and arcs will result in a fullthickness rim in addition to the endothelial graft once the free anterior cap is removed (Figure 30-6). We recommend selecting a trephine punch diameter at least half a millimeter less than the bed diameter to prevent this from occurring (i.e. with a donor bed diameter of 9.0 mm, we recommend using a 8.5 mm or smaller trephine) (Editorial Note: An 8.5 mm trephine on a donor bed of 9.0 mm allows for a surgeon error of 0.25 mm).

The pre-cut tissue may be cut with the surgeon’s preference of trephine punch system. We recommend the

Figure 30-6: Choosing a punch diameter smaller than the bed diameter.

(A)Indicates the bed diameter, which is the extent of the anterior cap.

(B)Shows a well-centered punch using a punch diameter smaller than the bed diameter. This yields the desired partial-thickness endothelial graft after the anterior cap is removed. (C) Shows a punch diameter larger than the bed diameter. This yields undesired full-thickness edges once the anterior cap is removed. This may also occur if the punch is decentered and cuts outside of the anterior cap. We recommend using a trephine punch size at least 0.5 mm less than the bed diameter.

use of a trephine system that contains a white or lightcolored Teflon block for holding the donor cornea (e.g. Troutman trephine system) so that the centration mark and peripheral arc marks are more readily visible. The Troutman system’s block has a central hole that can be used to align the centration mark of the donor tissue. External operating room lighting directed on the donor corneal tissue can also aid in visualization of these marks. Regardless of the trephination system, care must be taken to handle the tissue without contacting and damaging the endothelial cells as in any corneal transplant surgery. We use a separate sterile table to perform the donor punching. The tissue is placed on the punch block, endothelial side up, and then centration visually confirmed. The tissue can then be cut with the individual system’s trephine punch per the manufacturer’s instructions. This will yield the donor rim and the donor button (Figures 30-7A to C). The donor rim should be examined to ensure that the punch was centered within the three arcs. If the trephination occurred outside of the three arcs, then the excess full-thickness rim tissue must be carefully trimmed with Vannas scissors from the donor button before it can be used as a partial-thickness graft. Otherwise, the excess tissue can potentially interfere with full apposition of the donor graft against the posterior stroma of the host. The donor rim can then be sent for the usual testing similar to a PKP. The endothelium of the donor

button should then be protected with either Optisol-GS or a small amount of cohesive viscoelastic (i.e. Healon) and kept covered until transplantation into the recipient cornea.

Transplanting the Tissue

At this point, the donor button is the same as if the surgeon had cut the tissue himself or herself (see Table 30-1). It consists of an anterior stromal layer (cap) and the posterior endothelial graft. The only addition is the inked letter “S” on the stromal side of the endothelial graft. Once Descemet’s membrane has been stripped and the host corneal bed prepared, the donor button is brought into the surgical field. The endothelial graft is carefully separated from the anterior stromal cap and then delivered into the anterior chamber by the surgeon’s preferred method (Figures 30-8A to D). Once these graft is unfolded and tamponaded against the host stroma by either balanced salt solution or air, the surgeon must verify the stromal side from the endothelial side of the graft. If the letter “S” of the graft is seen through the cornea, then the stromal side is up, and the endothelial side is appropriately oriented (Figure 30-9). If the reverse is seen (“Z”) (Editorial Note: “reversed-S”), then the endothelial side is incorrectly contacting the host stroma, and the graft must be carefully reoriented (Editorial Note: If there is excessive

Figure 30-9: Successful placement of pre-cut endothelial graft into host. Here the letter “S” is seen, which helps confirm the correct orientation of the posterior lamellar graft (stromal side up and endothelial side down). If a backwards “S” or “Z” is seen, then the graft is incorrectly positioned upside down and must be inverted into the correct orientation.

endothelial damage due to improper disk orientation and tissue handling, a disk exchange may become necessary). Once the disk is properly oriented, centered, and tamponaded, then the case is concluded in the surgeon’s usual fashion.

Discussion and Outcomes

As with any technique, there are benefits and drawbacks of using pre-cut tissue for DSEK. The surgeon has advance information regarding the specific characteristics of the precut tissue that can help anticipate various issues during surgery (i.e. handling of a very thin or thick posterior graft, and the limits of the DSEK graft diameter). Secondly, the tissue-processor assumes the responsibility of cutting the tissue for DSEK. If a surgeon buttonholes a graft or generally performs a poor lamellar dissection intraoperatively, this will impede, if not potentially end, the progress of the case. A trusted tissue-processor, though, would be responsible for delivering only suitably cut tissue for DSEK

transplantation [Editorial Note: This may be considered as a partial modification from “surgery by surgeons” (see also Table 30-1)]. Thirdly, a reliable DSEK tissue-processor will have extensive experience cutting grafts specifically for DSEK. As an example, OSI has prepared over 500 corneas in a year for their client surgeons. Freeing the surgeon from performing the lamellar dissection also reduces case time in the operating room, decreasing the patient’s time under anesthesia and the costs associated with increased operating room time (Editorial Note: There is an added cost for pre-cut donor corneal tissue see Table 30-1). The costs of acquiring and maintaining an ALTK or similar dissection system are also assumed by the tissue-processor and not the surgeon – in the pre-cut tissue model. The ability to order the desired number of precut DSEK grafts also allows the surgeon to successively schedule the appropriate number of DSEK cases on the same operative day without having to wait on the sterilization and cooling of a microkeratome system which can delay the operating room schedule.

However, using pre-cut DSEK tissue has its disadvantages as well. The tissue-processor or eye bank will typically charge a fee for performing the lamellar dissection. This fee currently ranges from $ 500 to $ 1000 (US dollars) per graft depending on the supplier. Aside from financial considerations, not every surgeon may feel comfortable having a third party perform the donor tissue dissection beforehand. Another question is whether using pre-cut tissue instead of intraoperatively-cut tissue affects the outcome for the patient. As DSEK is a recently popularized procedure and the availability of pre-cut tissue is even more recent, few studies regarding the use of pre-cut DSEK tissue have been published.

Carlson and colleagues examined the endothelial cell density after the preparation of ten research corneas for DSEK. There was a 2.5% and 11.3% decrease in endothelial cell density at 48 and 72 hours post-section.6 As a comparison, whole human corneas stored in Optisol-GS have been shown to have an average decrease in endothelial viability of 9.5% after 96 hours.7 Functionally, the presumed result of this endothelial cell loss would be an increase in graft thickness. Griffin has shown that in 12 pre-cut DSEK tissues, the increase in thickness of the endothelial graft from the time of third-party microkeratome dissection to surgeon’s insertion the following day averaged only 7 μm (5%).8 The clinical implications of these results are still not known. At our institution, we have used only pre-cut tissue since we began performing DSEK. A review of our first 50 cases shows a graft dislocation rate of 12%.9 As a comparison, Price reported an overall dislocation rate of 16% in his first 200 cases.4 However, it should be noted

that both Price’s and our data are heterogeneous, and thus do not lend themselves to easy direct comparison. With more time, we expect that more basic science studies and larger, case-controlled comparisons of pre-cut versus intraoperatively-cut DSEK tissue will provide more information regarding the outcomes of using pre-cut tissue.

Conclusion

The recent availability of pre-cut donor tissue in DSEK frees the surgeon from the cost of investing in specialized corneal dissection instrumentation, minimizes the time-consuming dissection of the donor graft in the operating room, and eliminates the potential complications associated with intraoperative cutting of the donor tissue (i.e. button-holing, perforation, decentration). Using pre-cut tissue does not alter the overall DSEK procedure; the surgeon need only be aware of the cut bed diameter and the marks indicating the endothelial graft orientation. Not all surgeons, however, may be comfortable with having a third party prepare the graft, and there is currently a lack of peer-reviewed literature comparing the outcomes of DSEK using pre-cut versus surgeon-cut grafts. We recommend that the interested surgeon research the tissue-processor or eye bank of choice to inquire about the availability of pre-cut DSEK tissue and to develop a trusted, working relationship with the facility in providing quality endothelial grafts for this exciting advance in corneal transplantation surgery.

References

1. Melles GR, Egglink FA, Lander F, Pels E, Rietveld FJ, Beekhuis WH, Binder PS. A surgical technique for posterior lamellar keratoplasty. Cornea 1998;17(6):618-26.

2. Melles GR, Wijdh RH, Nieuwendaal CP. A technique to excise the descemet membrane from a recipient cornea (descemetorhexis). Cornea 2004;23(3):286-8.

3. Terry MA, Ousley PJ. Deep lamellar endothelial keratoplasty visual acuity, astigmatism and endothelial survival in a large prospective series. Ophthalmology 2005;112(9):1541-8.

4. Price FW, Price MO. Descemet’s stripping with endothelial keratoplasty in 200 eyes. J Cataract Refract Surg 32:411-8.

5. Kang PC, Klintworth GK, Kim T, Carlson AN, Adelman R, Stinnett S, Afshari NA. Trends in the indications for penetrating keratoplasty, 1980-2001. Cornea 2005;24(7):801-3.

6. Carlson AN, Lee AC, Afshari NA. Endothelial cell viability of pre-cut corneal donor tissue for endothelial keratoplasty. Invest Ophthal Vis Sci 2006; 47: E-Abstract 2355.

7. Means TL, Geroski DH, Hadley A, Lynn MJ, Edelhauser HF. Viability of human corneal endothelium following Optisol-GS storage. Arch Ophthalmol 1995;113(6):805-9.

8. Griffin NB. Thickness changes in donor tissue prepared and stored for DSEK. Paper presentation at the American Academy of Ophthalmology Annual Meeting 2006.

9. Chau F, Kim T, Carlson AN, Stinnett S, Afshari NA. Risk Factors for Donor Tissue Dislocation after Descemet Stripping Endothelial Keratoplasty (DSEK). Poster presentation at the American Academy of Ophthalmology Annual Meeting 2006.

Introduction

“No-stitch” (no corneal sutures) corneal transplant is an increasingly popular surgical procedure, both in the United States and globally that threatens to take the place of fullthickness penetrating keratoplasty (PKP) over time. Such surgical procedures like deep lamellar endothelial keratoplasty (DLEK)1-13 and Descemet stripping automated endothelial keratoplasty (DSAEK)14-21 requires working on the inner corneal surface of the patient’s cornea while removing a host corneal disk in DLEK or Descemet’s membrane (DM) with endothelium in DSAEK and replacing it with a donor corneal disk with healthy endothelium in the process of surgical, visual rehabilitation of the patient.

I introduced a new term for these types of surgeries namely, Selective Tissue Corneal Transplant (STCT).20 STCT may be viewed as a superior surgical procedure as compared to full-thickness corneal replacement surgery such as a PKP. STCT does not violate the patients corneal surface and thus avoids any induced surgical astigmatism, has no corneal sutures and hence it eliminates any suturerelated complications including breakage of corneal sutures, suture induced corneal neovascularization and possible infection including keratitis and corneal ulceration. Unlike a PKP, there is no full-thickness corneal wound in either DLEK or DSAEK and hence, the patient’s

cornea maintains the globe integrity and will be less prone to corneal rupture following traumatic injury to the eye.

The wound architecture is very interesting in DLEK and DSAEK. In DLEK, a pocket is surgically created within the stroma of the patient’s cornea without perforating either to the surface or into the anterior chamber (AC) (See chapters on DLEK). This requires some amount of expertise in lamellar keratoplasty. The intrastromal pocket extends to almost the full diameter of the patient’s cornea up to the limbus. Following the creation of this intrastromal pocket, a Terry trephine (Bausch & Lomb, Inc., Rochester, NY) is gently inserted into this intrastromal pocket and a posterior corneal trephination is carried out. This surgical step is performed after injecting a viscoelastic, such as Healon 5 (Advanced Medical Optics, Santa Ana, CA) into the AC prior to the posterior corneal trephination (see above). Next, a specially designed surgical scissors, called Cindy scissors (Bausch & Lomb, Inc., Rochester, NY) is used to excise the trephined posterior host corneal disk and it is removed using a 0.12 forceps. Removal of such a host corneal disk results in the creation of a circular recess in the posterior, inner corneal surface of the patient’s cornea (Figure 31-1A). Such a recess may be compared to a manhole (Figure 31-1B). This corneal recess is then closed with a donor corneal disk (Figure 31-2A) comprising of posterior corneal stroma, DM and healthy donor corneal endothelium. This

Figure 31-2: (A) The donor disk is attached to the recipient cornea in DLEK. The donor corneal disk comprising of stroma, Descemet’s membrane, and healthy endothelium has to be placed precisely within the recipient corneal wound. A reverse Sinskey hook is used along the margins of the donor disk 360 degrees (running-the-rim) to prevent any “edgeoverride.” This donor corneal disk is held in place primarily by the surrounding tissue forces and to a lesser extent by a large air bubble within the anterior chamber. (B) The attachment of the donor corneal disk to the recipient cornea is compared to a manhole being covered with the manhole cover.

Figure 31-1: (A) Schematic representation of DLEK surgery, showing the posterior corneal recess within the recipient cornea and the donor disk. (B) Cartoon depiction of the corneal wound being compared to a “manhole” and the donor corneal disk is compared to the manhole cover.