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

Introduction

Surgical endothelial replacement for conditions such as Fuchs’ endothelial dystrophy and pseudophakic bullous keratopathy has been successfully accomplished with fullthickness penetrating keratoplasty (PKP) for nearly 100 years (See also Chapter 14, History of Lamellar and Penetrating Keratoplasty).1 While the surgical technique of PKP is straightforward and relatively easy, the visual results and stability of the grafted corneal tissue are sometimes poor due to wound healing and suture-related problems.2-6

In 1993 Ko and Feldman presented an animal study at ARVO which described a new technique for endothelial replacement through a scleral limbal incision7 (See also Chapter 14, History of Lamellar and Penetrating Keratoplasty). In 1998, Melles et al described this technique in the first human patients and called it posterior lamellar keratoplasty8 (See also Chapter 14, History of Lamellar and Penetrating Keratoplasty). Terry and Ousley began laboratory work in 1999 on this technique, and after technical modifications and re-design of instrumentation, performed the first United States cases in 2000 and called the surgery Deep Lamellar Endothelial Keratoplasty (DLEK)9-20 (See also Chapter 14, History of Lamellar and Penetrating Keratoplasty).

All of this work represents a radical departure from the PKP technique in that the DLEK surgery accomplished the goal of endothelial replacement without any surface incision on the recipient cornea. By eliminating surface corneal sutures and incisions, the advantages of preserving the preoperative corneal topography and faster wound healing were obtained, leading to faster visual rehabilitation and a more stable globe for the patient.10-14

While undoubtedly there will be further refinement of the technique and instrumentation in DLEK surgery, it is the purpose of this chapter to describe in detail a method of DLEK that has been proven (with prospective data) to work and to provide considerable advantages over standard PKP surgery.

Surgical Objective

The purpose of DLEK surgery is to remove the diseased recipient endothelium and replace it with a healthy donor corneal endothelium. The advantage of DLEK surgery over PKP surgery is that it accomplishes this primary objective without violating the surface of the cornea with sutures or incisions. We have delineated the five ideal goals for endothelial replacement in previous papers as being (1) a smooth surface topography without significant change in astigmatism, (2) a highly predictable (and unchanged) corneal curvature, (3) a healthy donor corneal endothelium

which resolves all edema, (4) a tectonically stable globe, safe from injury and infection, and (5) an “optically pure” cornea.11,12,15-18 While standard PKP can consistently achieve good results for goals 3 and 5, the other goals have remained elusive.21-25 At the current time, DLEK surgery can accomplish the first 4 goals nearly perfectly, while the fifth goal of an optically pure cornea is good, but can still be improved. Instrumentation and technique modification to achieve a more perfect stromal interface between posterior donor tissue and anterior recipient tissue are the current directions of DLEK research.

Preferred Anesthesia

DLEK surgery is usually done under general anesthesia, but retrobulbar block anesthesia has also been used. General anesthesia (either endotracheal or laryngeal mask airway technique) is preferred because it minimizes posterior pressure on the globe and this is important during the recipient resection and donor implantation phases of the surgery. Nonetheless, the surgery can be safely accomplished with good retrobulbar anesthesia combined with seventh nerve block (orbicularis block) local anesthesia as well. It is possible, in the severely medically frail patient, that this surgery could be accomplished with only topical anesthesia, similar to what has been done in PKP surgery under similar circumstances.26 However, this has not yet been done with DLEK surgery and likely would require a surgeon with the ability to accomplish this surgery in less than an hour.

Preoperative Preparation

Like all intraocular procedures, the patient’s ocular health should be maximized prior to surgery and any blepharitis, dry eye, or lid abnormality should be treated before the DLEK surgery. Patients with some mild to moderate corneal surface haze or scarring from long-standing bullous keratopathy can still undergo DLEK surgery successfully. The surface scarring is simply scraped off at the time of surgery or weeks later in the clinic after the stromal edema has completely resolved. This eliminates the induced irregular astigmatism from the scars and restores normal corneal topography.

In patients with pseudophakia, the pupil is constricted in order to stabilize the iris-lens diaphragm during the surgery. This is also done if the patient has a clear crystalline lens and concurrent cataract surgery is not planned. Preoperative medications include two sets of pilocarpine 1% drops applied one hour prior to surgery. One set of aproclonidine 0.5% drops is also given just prior

to surgery to reduce pressure and minimize conjunctival injection. No preoperative antibiotics are necessary. The eye is prepped in the usual sterile ophthalmic fashion with the use of povidone-iodine solution.

In the case of patients with cataract and endothelial failure, then cataract surgery is performed just prior to the DLEK endothelial transplant and the pupil is dilated preoperatively with the surgeon’s preferred dilating drops for cataract surgery. While pilocarpine is avoided, the rest of the preoperative medication regimen described above is utilized.

DLEK Surgical Procedure

Recipient Surgery

For large incision DLEK surgery, the scleral access incision is 9.0 mm, and therefore the incision is usually placed at the superior limbal region (Figure 15-1) rather than temporally. The patient’s head is positioned with the chin up and the forehead back to minimize brow obstruction of the surgical field. In addition, the endotracheal tube is also positioned by the anesthesiologist to exit the mouth from the side opposite the surgical field to facilitate the surgeon’s field of movement. A superior and inferior rectus bridal suture can also be placed to aid in positioning and stabilizing the globe during DLEK surgery.

Figure 15-1: Preoperative appearance

A superior limbal peritomy of the conjunctiva is performed with scissors (Figure 15-2) allowing exposure of the superior 10.0 mm arc length of limbal tissue. Prior to forming the DLEK scleral access incision, two clear corneal limbal stab incisions of about 1.0 mm in size are placed on either side of the peritomy area (Figure 15-3) , to be used as access points to the anterior chamber later in the operation. Through one of the stab incisions, the cohesive viscoelastic Healon (Pfizer, New York, NY) is placed into the anterior

Figure 15-2: Superior limbal peritomy.

Figure 15-3: Clear corneal stab incision.

Figure 15-4: Viscoelastic into the anterior chamber.

chamber (Figure 15-4) to replace the aqueous fully and to maintain normal pressure. It is important not to use Viscoat (Alcon, Fort Worth, TX) or other dispersive viscoelastic materials during any portion of DLEK surgery as the dispersive materials can cause stromal interface coating with subsequent non-adherence and dislocation of the donor tissue.

Figure 15-5: A 9.0 mm diamond knife incision.

A trifaceted, guarded diamond knife is then set to a depth of 350 microns and a 9.0 mm incision is made approximately 1.0 mm posterior and concentric to the corneal limbus (Figure 15-5) . We have found that a deeper initial incision gives less of a beveled wound closure and also a greater chance of early perforation into the anterior chamber during

DLEK surgery. In lieu of a diamond knife, a sharp crescent blade or other steel scalpel can be used for the initial incision. A sharp crescent blade is then utilized to create a deep scleral-corneal lamellar pocket down to about 75 to 85% corneal depth along the entire length of the wound (Figures 15-6A and B). Perfect accuracy of the depth of the corneal stromal pocket does not appear to be critical for a good visual outcome.27 Pockets should be deeper than 50% in order to avoid interface scarring or haze, and should not exceed 95% depth in order to avoid a mismatch of the donorrecipient corneal thickness. Judgment of the initial depth of the pocket is based upon inspection of the anterior lip thickness and by the clarity of the underlying stromal bed. Obviously, experience with the DLEK procedure and with lamellar dissections in general aids in the surgeon confidence that the desired depth has been achieved.

A specialized semi-sharp stromal dissector is then used to extend the pocket to the mid-pupillary region of the cornea (Figures 15-7A and B) and then a curved stromal dissector (Figures 15-8A and B) (Devers Dissector, Bausch and Lomb, St. Louis, MO) extends the pocket completely to

A

B

Figures 15-8A and B: Curved Devers dissector.

the limbus for 360 degrees, creating a total area, deep lamellar corneal pocket. The Devers Dissectors are designed with a tip that is not as sharp as a crescent blade, but is sharper than a blunt dissector. The width of the dissecting heads are especially good for maintaining the stromal depth consistently throughout the dissection of the edematous deep stroma and the surgeon can actually feel the increased resistance to dissection if he/she deviates too anteriorly. The dissection is accomplished with a slow and methodical sweeping motion of the dissector heads, from central to peripheral tissue, and the surgeon can often see the reflections of Descemet’s membrane wrinkling during the sweeping motion, which is an assurance that the depth of the dissection is adequate. It is important that the pocket stromal dissection be carried out over the entire area of the cornea, extending it all the way to the limbus for 360 degrees, in order to allow adequate space for the intralamellar trephine.

The resection of the posterior recipient tissue begins by first softening the globe with the release of Healon through the stab incisions (Figure 15-9) from the anterior chamber. A specialized intrastromal trephine (Figure 15-10) (Terry

Figure 15-9: Release of Healon from paracentesis wound.

Figure 15-10: Terry trephine displayed.

Figure 15-11: Terry trephine in pocket.

trephine, Bausch and Lomb, St. Louis, MO) is then placed into the stromal pocket (Figure 15-11), taking care to position it centrally in the cornea. Once the blade is in position, additional Healon is placed into the anterior chamber to raise the pressure of the anterior chamber and provide a “back-pressure” for the trephination. The Terry

trephine comes in diameters of between 7.0 mm and 8.5 mm in 0.5 mm increments, with the most common diameter of 8.0 mm used in our prospective clinical series.10-13 The circular blade has a profile height of 250 µm and is intended for one-time use. In reality, a well cared for blade can be used 3 or 4 times with good clinical results before it requires re-sharpening or replacement. Once the circular trephine blade has been inserted into the pocket, the surgeon grasps the knurled handle and rotates the trephine in the same manner as a standard surface hand-held free trephine blade. The globe may need to be stabilized with a separate forceps for the rotational cut to be made effective. The blade is rotated clock-wise and counter clock-wise along the arc length of the 9.0 mm scleral incision. It makes the surgery easier if the initial point of entry into the anterior chamber is at the distal position of the cornea (i.e. the 6 o’clock position), and so the surgeon pushes down on the blade slightly greater at 6 o’clock than at 12 o’clock position, during rotation of the Terry trephine. As soon as the intrastromal Terry trephine enters the anterior chamber, the Healon in the anterior chamber enters the interface, the pressure drops, and the trephination is stopped. If the entry point is distal as hoped, then another entry into the anterior chamber is made at the 12 o’clock position with a diamond or steel keratome. This is placed through the superior scleral wound, into the pocket and then perforating into the anterior chamber at the 12 o’clock trephination mark. It is through this entry point that the recipient posterior resection is completed utilizing special scissors designed for posterior lamellar tissue resection (Cindy I and Cindy II Scissors, Bausch and Lomb, St. Louis, MO). The Cindy I scissors are placed with one blade in the anterior chamber and one blade in the stromal pocket. The scissors complete the trephination cut, following the mark of the circular trephination made previously by the Terry trephine (Figures 15-12A and B). The Cindy I scissors have long, highly curved and low profile blades and are ideally suited for this procedure. Once the resection has progressed distally to about the 5 o’clock and 7 o’clock positions, then the Cindy II scissors are utilized for completion of the distal resection. The Cindy II scissors have long, low profile blades that are set at nearly a right angle to easily complete the more difficult distal resection. If the Terry trephine had entered the anterior chamber over 2 or 3 clock hours distally as earlier intended, then the Cindy II scissors are not needed and the resection is completed faster and more easily. Once the posterior recipient disk has been cut 360 degrees, then the tissue is removed from the eye (Figures 15-13A and B) and placed on the corneal surface for inspection. It is washed with balanced salt solution (BSS, Alcon, Fort Worth, TX), and dried with a sponge (Figure 15-14) . The stromal

A

B

Figures 15-12A and B: Cindy scissors completion of resection.

surface is inspected for smoothness and the edges for regularity of cut, as well as the thickness of the resected tissue. With the removal of the recipient posterior edematous stromal tissue, the view into the anterior chamber through the central cornea clears significantly (Figure 15-15) , and often other intraocular surgery such as vitrectomy, IOL exchange, and iridoplasty can be performed at this stage of the DLEK procedure.

After removal of the recipient posterior tissue, the superior scleral wound is temporarily closed with 3 interrupted 10-0 nylon sutures. An irrigation/aspiration tip is then introduced into the anterior chamber and extensive effort is expended to remove all of the viscoelastic material from the eye (Figure 15-16) . There should be no Healon left in the anterior chamber prior to insertion of the donor disk or the donor tissue will not “stick” in place. Therefore, care is taken to irrigate and aspirate the anterior chamber, pupillary area, angle, and even the peripheral pocket as necessary. Once the surgeon is confident that all Healon has been removed, then the eye pressure is left slightly soft and attention is turned to preparation of the donor.

A

B

Figures 15-13A and B: Recipient disk removal.

Figure 15-14: The recipient disk is irrigated with balanced salt solution and dried with a sponge.

Donor Tissue Preparation

The operating microscope is brought over to the separate donor table for preparation of the donor tissue. Because whole globes are rarely available in the United States, an artificial anterior chamber is necessary for preparation of the donor posterior disk. We utilize a Bausch and Lomb

Figure 15-15: Clearing of cornea after recipient disk removal.

Figure 15-16: I/A removal of Healon.

(St. Louis, MO) artificial anterior chamber (AAC) (See also Chapter 12, Artificial Anterior Chambers) that is all stainless steel and has dual irrigation/aspiration ports. The OptisolGS preservation fluid (Bausch and Lomb, Rochester, NY) from the donor tissue container is aspirated into a syringe and is then used to fill the I/A ports of the AAC. The syringe is also attached to the port to be used to vary the pressure inside the chamber for the duration of the resection. The standard donor corneoscleral cap tissue is first coated with a thin layer of Healon on the endothelium (Figure 15-17). It is then placed endothelial side down onto the post of the AAC (Figure 15-18) and oriented with the largest diameter of the cornea in the horizontal meridian. This meridian is marked with a marking pen so that the horizontal meridian of the donor tissue can be identified later in the procedure. The donor tissue is capped into place and the chamber is filled with Optisol-GS and the pressure normalized. An 8.5 mm diameter Barron suction recipient trephine (Katena Products, Denville, NJ) is placed onto the surface of the donor tissue and suction is applied (Figure 15-19). Trephination is carried out to about 60% depth with the trephine. It is noteworthy that after the blade touches the

Figure 15-17: Healon on endothelium.

Figure 15-20: Dissection of donor cornea.

Figure 15-18: Cornea placement onto artificial anterior chamber.

Figure 15-19: Barron recipient trephine.

epithelial surface of the donor, it only takes about 4 or 5 quarter turns of the Barron radial vacuum trephine to reach this depth. This is much sooner than when the same trephine is used on the recipient in standard PKP surgery. The trephine is then removed and the cut inspected for depth. Ideally, an 80% depth should be attained for the

plane of the pocket of the donor tissue. Any deeper than this, and the donor tissue is so thin that it spontaneously rolls up like a rug causing confusion as to which side is the endothelial side and undoubtedly causing endothelial damage. If the dissection depth of the donor is less than 60% depth, then the stromal surface may not be as smooth and the tissue may be much thicker than the depth of the recipient bed. However, whether disparity between donor and recipient disc thicknesses causes a later visual problem is unknown at this time. Similar to the recipient disc preparation, the crescent blade is used to cut down to the 80% depth (Figure 15-20) and this depth and pocket is then extended over the entire area of the cornea, all the way to the limbus 360 degrees, using the straight and curved Devers Dissectors (Bausch and Lomb).

After completing the deep stromal pocket formation, the cap of the chamber is gently rotated, taking care not to collapse the chamber, and the cap is removed. The donor tissue is then left on the post with a formed chamber. The scleral edges of the donor are gently lifted to release the tissue and the tissue is removed from the post, once again taking care not to collapse the chamber and damage the endothelium. After the tissue is lifted off the post, the endothelial side is gently irrigated with BSS to remove excess Healon and prevent it from contaminating the stromal pocket during the next stage of the preparation.

The donor tissue is then placed endothelial side up onto a standard punch trephine block (Figure 15-21). Barron donor punch (Katena, Denville, NJ) is used. The same size diameter punch is used as the diameter of the Terry Trephine used for the recipient resection. A diameter 0.25 mm larger for the donor has been used, but the incidence of donor folds and dislocations increased with this disparity (unpublished data). The tissue is punched out with the trephine (Figure 15-22) , and if the dissection has been done properly, the surgeon will not hear that