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

Infection

John T first described a new clinical entity namely, “sandwich keratitis” following DLEK in 2003.4 In selective tissue corneal transplantation1-3 only the diseased portion of the patient’s cornea is surgically removed and replaced with a similar, healthy donor corneal tissue, and in so doing, it results in an interface between the donor and the recipient corneal surfaces. Any infectious agent(s) inadvertently introduced into this potential space at the interface during surgery gets “trapped” between the two tissue layers and be localized in that region. Since the infection occurs between two layers of the cornea much like a sandwich, the term “sandwich keratitis was given to this clinical entity (Figures 28-28 and 28-29).4

In sandwich keratitis, the patient may not be symptomatic in the early stages and the eye may not be significantly red, except for the redness usually noted after surgery. This often can result in a delay in diagnosis and management. These findings both symptoms and signs are quite different from the usual corneal ulcer that begins from the corneal surface and progresses into the corneal stroma. In the corneal ulcer that starts from the corneal surface, the

Figure 28-28: Sandwich keratitis 6 weeks after a DLEK procedure. The infectious organisms are located in the donor-recipient interface.

patient presents early while in sandwich keratitis the patient may present much later.

Unlike a corneal ulcer where the topical antibiotics will achieve high concentration in the region of the ulcer, in a sandwich keratitis the antibiotics have to reach the interface

Figure 28-29: Transmission electron micrograph of the donor-recipient interface in a case of sandwich keratitis following DLEK, showing

Candida (Torulopsis) glabrata (arrow) surrounded by Staphylococcus sp.

and hence the concentration will be lower than that will be achieved when treating a surface corneal ulcer.

In a surface corneal ulcer that fails medical treatment and goes onto a therapeutic keratoplasty, one of the main concerns is usually infection free margins. In a sandwich keratitis the same applies, but in addition it is important

not to open the sandwich during a therapeutic keratoplasty, since the organisms from the interface can spill into the anterior chamber, converting a sandwich keratitis to a potential endophthalmitis and even loss of the eye.

This new clinical entity, namely sandwich keratitis should be recognized by clinicians and treated appropriately, as there is a continued trend in the direction away from a full-thickness penetrating keratoplasty to a selective tissue corneal transplant technique such as DSAEK, DLEK, DMEK, and all types of ALKs, all of which can result in a donor-recipient interface infection called, sandwich keratitis.

References

1. John T. Selective tissue corneal transplantation: a great step forward in global visual restoration. Expert Rev Ophthalmol 2006;1:5-7.

2. John T. Surgical Techniques in Anterior and Posterior Lamellar Keratoplasty. New Delhi, India: Jaypee Brothers Medical Publishers; 2006:1-687.

3. John T. Step by Step Anterior and Posterior Lamellar Keratoplasty. New Delhi, India: Jaypee Brothers Medical Publishers; 2006:1-297.

4. John T, Delany C, John ME. Sandwich keratitis: New clinical entity following deep lamellar endothelial keratoplasty. Presented at the Annual Meeting of the American Society of Cataract and Refractive Surgery, San Francisco, CA, April 1216, 2003.

Terminology

Descemetorhexis with endokeratoplasty (DXEK) is synonymous with Descemet’s stripping with endothelial keratoplasty (DSEK), and Descemet’s stripping automated endothelial keratoplasty (DSAEK) (See also Section 9, Descemet’s Stripping Automated Endothelial Keratoplasty). The term DSAEK will be used in this chapter, since it is a more commonly used term.

Unanswered Questions in DSAEK

In DSAEK, first a centrally placed circular area of the inner corneal surface of the patient’s cornea is operated upon to expose the recipient corneal stroma.1-9 Unlike deep lamellar endothelial keratoplasty (DLEK)10-16 [See also Section 8, Deep Lamellar Endothelial Keratoplasty (DLEK)], there is no posterior corneal recess in DSAEK. The recipient cornea is intact except for the absence of a circular area of Descemet’s membrane (DM) with its attached endothelium. Next, the donor corneal disk is attached to this area of exposed corneal stroma in the inner surface of the patient’s cornea

(See also Section 9, Descemet’s Stripping Automated Endothelial Keratoplasty).

The surgical approach of adding a disk of donor circular tissue to the surface of another tissue/organ namely, the patient’s cornea, is a very rare approach, if not the only one of its kind in the whole field of transplant surgery. Additionally, the attachment is done without any sutures or tissue adhesives of any kind. In any segmental tissue transplantation, the edges of the transplanted tissue are usually approximated to the edges of the host tissues to which the transplantation is performed. Such tissue-to- tissue contact results in contact inhibition and prevents any tissue expansion. Since there is no edge-to-edge approximation in DSAEK surgery, this may be considered as a “step-up-stage” type of tissue addition procedure. In this case, the “stage” is the circular disk of tissue and the “ground level’ would be the patient’s cornea. The edge of this “stage” is the cut-edge of the donor corneal stroma, DM, and endothelium. Thus, the cut-edge of the donor corneal disk is fully exposed and bathed in the aqueous humor within the anterior chamber.

Since, the cut-edge of the donor corneal disk is exposed; does this translate to expansion of these tissues onto the inner surface of the patient’s cornea? Does this mean that the stromal keratocytes will extend onto the surrounding patient’s inner cornea? Although the endothelial cells for the most part do not multiply, will the donor endothelial cells slide outward and extend onto and over the patient’s endothelium? If so, will the expanded endothelial cell layer

lay down new DM? Will such potential cellular expansion, if it occurs over time, extend onto the anterior chamber angle, iris surface, and progress further, resulting in peripheral anterior synechiae, secondary angle closure glaucoma, and pupillary abnormalities? The answers to these questions are currently not available since the DSAEK procedure has a short time track from its inception to the present time (at the time of writing this chapter). In the future, as some of the DSAEK corneas undergo graft rejection and graft failure, and go on to possible full-thickness penetrating keratoplasty (PKP), these corneas will provide the answers to some of the above questions, as these tissues are then studied in the ophthalmic pathology laboratories.

The interface relates to the area of contact between the donor and the recipient corneal stroma. This interface moves from the mid-stromal region of the recipient cornea in DLEK to a more posterior region of the recipient cornea namely, the posterior corneal stroma close to the level of the excised DM of the recipient cornea in DSAEK. This posterior shift in the interface is believed to have a positive effect on the overall quality of vision following DSAEK. This interface is more noticeable in the immediate postoperative period following DSAEK and it becomes less prominent, to almost non-visible in some cases, over time. The question arises as to what extent does the donor-host tissue integration take place? We do know that initially this tissue integration is not pronounced and the donor disk can be removed with relative ease. However, it becomes more difficult to remove a disk that has been in place for several months following DSAEK. Does this imply that there is extensive tissue remodeling and integration over time? These questions will be answered as we study these tissues when they become available over time. The author’s experience has shown keratocyte activation, wound healing, and tissue integration at the level of the donorrecipient interface.17

In DSAEK, the edge of the donor corneal disk overlaps the cut-edge of the host endothelium and DM. Since the cut-edge of the host endothelium is “free” without any cellular contact inhibition, will these endothelial cells expand into the donor-host interface to interfere with the interface clarity? The answer to this question is possibly a “no.” The reason being, there is direct contact between the host corneal stroma and the donor corneal stroma, and continued adhesion and remodeling that takes place between these tissues will allow for no free space for the host endothelium to slide into. Also, the host endothelium is usually not healthy and usually comprises of decompensated cells at the time of DSAEK surgery.

DSAEK surgery is an additive procedure. Donor corneal disk is added on to the host cornea, resulting in the final

thickness of the host cornea always being greater than the normal human corneal thickness. If a donor corneal disk of 150 µm thickness is added to a host central corneal thickness of about 520 µm, this will result in an increase in the host corneal thickness by about 29%.

In the above example, the host corneal thickness to begin with may be greater than 600 µm, which then gradually decreases in thickness as the healthy donor corneal endothelium clears the host cloudy cornea. The healthy donor corneal endothelium has to now function to clear a cornea with an increased thickness of about 29% or even greater depending on the donor corneal disk thickness and the final host corneal thickness. The question then arises what is the upper limit of total corneal thickness that a monolayer of healthy endothelium can keep clear? Is there an upper limit of total corneal thickness beyond which the endothelium will fail to function? Currently, these questions remain unanswered. To date, clinically the increased corneal thickness does not appear to have any known deleterious effects on the patient’s cornea or on the quality of vision.

References

1. John T. Corneal disk detachment. Annals of Ophthalmol 2006; 38:169-84.

2. John T. Selective tissue corneal transplantation: A great step forward in global visual restoration. Expert Rev Ophthalmol 2006;1:5-7.

3. John T. Descemetorhexis with endokeratoplasty. In: John T (Ed): Surgical Techniques in Anterior and Posterior Lamellar Corneal Surgery. Jaypee Brothers Medical Publishers (P) Ltd, New Delhi, India, 2006;411-20.

4. John T. Descemetorhexis with endokeratoplasty (DXEK). In:

John T (Ed): Step by Step Anterior and Posterior Lamellar Keratoplasty. Jaypee Brothers Medical Publishers (P) Ltd, New Delhi, India, 2006;177-96.

5. Melles GR. Posterior lamellar keratoplasty: DLEK to DSEK to DMEK. Cornea 2006;25:879-81.

6. Price FW Jr, Price MO. Descemet’s stripping with endothelial keratoplasty in 200 eyes: Early challenges and techniques to enhance donor adherence. J Cataract Refract Surg 2006;32: 411-8.

7. Mearza AA, Quershi MA, Rostron CK. Experience and 12month results of descemet-stripping endothelial keratoplasty (DSEK) with a small-incision technique. Cornea 2007;26: 279-83.

8. Price MO, Price FW. Descemet’s stripping endothelial keratoplasty. Curr Opin Ophthalmol 2007;18:290-4.

9. Terry MA, Ousley PJ. Corneal endothelial transplantation: Advances in the surgical management of endothelial dysfunction. Contemporary Ophthalmology 2002;1(26):1-8.

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

11.Terry MA, Ousley PJ. Endothelial replacement without surface corneal incisions or sutures: Topography of the deep lamellar endothelial keratoplasty procedure. Cornea 2001;20:14-8.

12.Terry MA, Ousley PJ. Deep lamellar endothelial keratoplasty in the first United States patients: Early clinical results. Cornea 2001;20:239-43.

13.Terry MA, Ousley PJ. Replacing the endothelium without corneal surface incisions or sutures: The first United States clinical series using the deep lamellar endothelial keratoplasty procedure. Ophthalmology 2003;110:755-64.

14.Terry MA, Ousley PJ. In pursuit of emmetropia: Spherical equivalent refraction results with deep lamellar endothelial keratoplasty (DLEK). Cornea 2003;22:619-26.

15.Marcon AS, Terry MA, Kara-José N, Wall J, Ousley PJ, Hoar K. Influence of final corneal thickness in visual acuity after deep lamellar endothelial keratoplasty. Cornea 2007;26:543-5.

16.Yepes N, Segev F, Hyams M, McAllum P, Slomovic AR, Rootman DS. Five-millimeter-incision deep lamellar endothelial keratoplasty: One-year results. Cornea 2007;26:530-3.

17.John T, Fraenkel GG, John ME. Keratocyte densities and interface changes in failed deep lamellar endothelial keratoplasty. Presented at the ARVO Annual Meeting, 2004.

Introduction

Over the last 250 years, corneal transplant surgery has progressed from a mere idea to a successfully practiced means of restoring corneal clarity and integrity for a multitude of patients. Similarly, within the last decade, posterior lamellar keratoplasty has been refined to provide a viable alternative to full-thickness transplantation for those with endothelial disease.1-4 As patients with endothelial disease (Fuchs’ dystrophy, aphakic/pseudophakic bullous keratopathy, and graft failure) comprise up to 40% of the recent full-thickness transplant population,5 Descemet’s stripping with endothelial keratoplasty (DSEK) represents a less invasive surgical advance that offers faster recovery than penetrating keratoplasty (PKP) for these patients.

Dissection of the donor corneoscleral tissue for DASEK is described elsewhere in Section 9, Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK) and in the literature.1-4 Recently, pre-cut allograft tissue from eye banks has become available for DSEK and can eliminate tedious and time-consuming intraoperative dissection of donor tissue for the DSAEK surgeon. In this chapter, we will discuss the third party’s preparation of the cornea for DSEK, our surgical technique for handling pre-cut DSEK tissue, and finally, our outcomes with pre-cut DSEK tissue.

Third Party Preparation of Corneal Tissue for DSAEK

Pre-cut DSEK tissue can currently be obtained from select eyebanks.Ourcenterutilizespre-cutDSEKtissuefromboth our local eye bank – The North Carolina Eye Bank (NCEB), as well as a private company, Ocular Systems Inc. (OSI; Winston-Salem, NC). While this chapter discusses the practicesofNCEBandOSIduetoourfamiliaritywiththem, there are other third party preparers of DSEK tissue nationwide.Regardlessofthesourceofpre-cutDSEKtissue, thesurgeonshouldpersonallyensurethattheinstitutionhe orshechoosestoprovidepre-cutDSEKtissuemeetsfederal regulations as well as the surgeon’s standards.

Whenarequestfortissueisreceived,therearetwomodels fortheacquisitionoftissue.Foraneyebank,thismaysimply mean redirecting appropriate corneal tissue on hand for DSEKcutting,whileaprivatecompanywouldobtaincorneal tissuefromapartneringeyebank.Oncethetissueisacquired, both models will subject the tissue to administrative and medical verification for appropriateness of use. The donor tissue is screened for concerning medical history, positive orreactiveinfectioustesting,andpoorendothelialcellcounts or tissue quality. An eye bank may perform the testing and

specular microscopy in house, while a private company willrelyontheinformationsuppliedbytheirpartneringeye bank. In addition, a private company will also examine detailsspecifictothetransitofthetissuefromtheirpartner, suchasshippinginformation,intactpackagingandcarrier, andstorage/refrigerationconditions.Forbothmodels,the carriermediawillbeinspectedforcolorandclarity,andthe donor tissue itself examined under high magnification for defects or unusual endothelial morphology. This is akin to the inspection process any ophthalmologist would undertake prior to using any donor tissue.

Oncethetissuepassesinspection,itisreadytobeprepared. The tissue carrier is brought into the clean room, and the tissue is prepared under sterile technique with sterile instrumentation. NCEB uses a NSF Type II laminar flow biosafety hood, while OSI utilizes a dedicated clean room withHEPAfiltered,laminarairflowthatisgradedClass100 (no more than 100 particles greater than 0.50 μm per cubic squarefootoftheworkarea).TocreatetheDSEKgraft,both NCEB and OSI use of an automated lamellar therapeutic keratoplasty (ALTK) system (Moria SA, Antony, France)

(See also Chapter 12, Artificial Anterior Chambers). The componentsanddetaileduseofthissystemaredescribedin

Chapter 12, Artificial Anterior Chambers. The corneoscleral donorofatleast16mmiscentered,mountedontheArtificial Chamber, and brought to appropriate pressure (Figure 30-1). An ultrasound pachymetry is then used to measure

Figure 30-1: NCEB tissue markings for pre-cut DSEK tissue. This diagram represents the donor tissue, epithelial side up. The cornea is light blue, while the sclera is cream colored. The inner-most circle represents the anterior cap cut by the ALTK system. NCEB places an alignment mark at the 12 o’clock position crossing both the anterior cap and the uncut tissue. In addition to a centering dot, NCEB places 3 additional marks just outside of the anterior cap to give a visual approximation of the bed diameter (anterior cap). NCEB places all of its marks on the epithelium only.

the full-thickness of the graft. A microkeratome head is selected and then used to cut the graft. OSI typically uses a 300μmmicrokeratomehead,reservingthe350μmheadfor tissue thicker than 575 μm. NCEB uses the same heads but will use a 250 μm head for tissue thinner than 500 μm. The resultingbeddiameter(anteriorcap)isthenmeasured.This is typically intended to be 9.0 mm to 10.0 mm.

At this point, the tissue is marked by the third party preparer with Gentian Violet [Editorial Note: Use of marking pen on the corneal stroma has been associated with endothelial cell loss (Terry M, personal communication)]. Each third party preparer may have its own unique method of marking the tissue and documentation forms (Figures 30-1 to 30-4), and the surgeon will need to familiarize himself or herself to the markings of their tissue provider. For instance, NCEB indicates the anterior cap with the dots shown in figure 1. On the other hand, OSI uses arcs to indicate the margins of the anterior cap and to clearly delineate its extent (diagram on lower half of Figure 30-3). Both preparers also create an anterior cap alignment mark.

The anterior cap is now temporarily removed. With the anterior cap removed, the stromal side of the endothelial graft is exposed. A pachymetry is taken on the exposed stroma to provide the endothelial graft thickness. This is generally between 100 to 150 μm depending on the original pachymetry of the donor tissue. OSI places additional graft polarity marks at this point: both a grossly visualized centering mark and an orientation mark (the letter “S”) are placed [Editorial Note: Stromal markings appears to be associated with endothelial cell loss (Terry M, personal communication) and hence, it may be advisable not to perform such markings]. The stromal surfaces are dried, and the anterior cap is replaced and repositioned based on the earlier alignment mark. The complete corneoscleral donor is then removed from the ALTK system and replaced into a new transport container with fresh Optisol-GS. The transport container is sealed and finally brought out of the sterile clean room, ready to be packaged for delivery to the surgeon. Most third party preparers will attempt to acquire tissue that can be implanted within five days postmortem and within 24 hours of DSEK preparation.

The pre-cut DSEK tissue from OSI comes packaged with three sheets of documentation. The first (Figure 30-2) is a cover sheet that reiterates that the pre-cut tissue be used only for endothelial keratoplasty and also contains the OSI tissue ID number, full-thickness and endothelial graft pachymetry, and legal information. Another sheet is labeled “Recipient Information Form” and is to be completed by the surgeon to be returned to OSI for patient tracking and quality control purposes. The sheet titled “Donor Summary

and Allograft Preparation Form” is the most important one for the operating surgeon (Figure 30-3). This sheet contains the donor information, the endothelial cell count, the pachymetry, the bed diameter, and the OSI processing times. It should be noted that the listed endothelial cell count is that provided by the original eye bank. OSI does not perform another endothelial cell count after preparing the tissue.

NCEB provides similar information in their documentation titled “EK Processing and Tissue Evaluation Form” as seen in Figure 30-4. NCEB does perform its own endothelial cell count and tissue examination post ALTK dissection, and this is reported on the form. NCEB also includes copies of the original paperwork from the tissue source.

Practical use of the information provided in the tissue documentation is described below under Surgical Technique. If you use a different pre-cut DSEK tissue provider, the documentation may differ, but it is important to locate the donor information, the endothelial cell count, the pachymetry, and especially the bed diameter within the documentation.

As described, the preparation of tissue for DSEK by either an eye bank or private tissue processor requires only a brief detour in the tissue’s transit from the donor to the surgery center. During this detour, the tissue preparer assumes the task of cutting the endothelial graft, thus making it ready for DSEK before it arrives in the surgeon’s hands in the operating suite.

Surgical Technique for Pre-Cut Corneal Tissue for DSEK

The use of pre-cut corneal tissue for DSEK does not change the overall techniques of the procedure. The surgeon must only be aware of how the pre-cut tissue has been cut and marked to help in centering the trephination and to help in confirming stromal and endothelial side of the disk. We use the tissue markings of OSI as an example in this section. There may be differences among the third-party preparers with regard to tissue markings.

Examination of the Tissue

As in all corneal transplant surgeries, the surgeon should examine the donor tissue prior to its use to confirm that the tissue is suitable for transplantation. This includes visual examination of the donor cornea, preferably under magnification, for signs of disease (opacities, vascularization, etc.). The included documentation provides information regarding the donor’s demographics, endothelial cell