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

eye, or lid abnormality should be treated prior to surgery. Patients with mild to moderate corneal surface haze or scarring from long-standing bullous keratopathy can still undergo DLEK surgery successfully. The surface scarring is scraped off at the time of surgery or weeks later in clinic after the stromal edema has completely resolved. This eliminates the induced irregular astigmatism from the scars and restores the normal 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 patients with cataract and endothelial failure, cataract surgery is performed just prior to the DLEK endothelial transplant and the pupil is dilated preoperatively (Figure 17-1) with the surgeon’s standard dilating drops for cataract surgery. While pilocarpine is avoided, the rest of the preoperative medication regimen described above is utilized.

Figure 17-1: Pre-operative appearance of the cornea.

Surgical Procedure: Combined

DLEK and Phacoemulsification

Recipient Surgery: Phacoemulsification Technique

Small incision phacoemulsification cataract extraction, when combined with DLEK surgery, is usually performed utilizing a sclerocorneal tunnel access incision, rather than

a clear corneolimbal incision. The reasoning behind this is that the cataract wound needs to be water tight and as strong as possible to withstand the manipulations and pressures placed on the eye during DLEK recipient tissue dissections. In addition, it is preferable to completely eliminate any surface corneal incisions of any kind to maximize the topographic advantages of DLEK surgery. Although, phacoemulsification can be performed through the same incision of the DLEK surgery after the recipient posterior corneal tissue has cleared the visualization of the anterior chamber, it is our preference to perform the cataract extraction portion of the procedure from a separate site from the DLEK surgery whenever possible. Therefore, we currently begin “The New Triple Procedure” (Terry and Ousley, AAO instructional video, 2002) with the phacoemulsification performed from the superior 12 o’clock position.

Most cases of Fuchs’ corneal endothelial dystrophy, corneal edema will allow adequate visualization of the anterior segment to safely complete the cataract surgery. However, high pressures within the eye during the phacoemulsification will force fluid into the already edematous cornea and create a foggy view. Therefore, the phacoemulsification wound is made long enough (usually 3.0 mm or more) to allow adequate egress of BSS during the phacoemulsification portion of the procedure and maintain an optimal corneal clarity. In some cases of advanced corneal endothelial decompensation, the preoperative corneal edema has created bullae on the central corneal surface, making visualization for cataract surgery difficult or impossible. In these cases, we have advocated one of the following remedies: (1) Apply sterile glycerin drops to the corneal surface to deterges the epithelial edema and improve the view of the anterior segment of the eye. This gives a very temporary effect of smoothing the surface and requires multiple applications; (2) Scrape the central 6 mm of the epithelium from the corneal surface to provide an immediate improvement in surface smoothness. This requires the use of a bandage contact lens or collagen shield at the end of the surgery and the application of a bandage contact lens during the 1st week following surgery. It does not seem to pose a risk to the later adhesion of the donor disk; or (3) Consider performing the cataract surgery through the same DLEK temporal wound, after the recipient tissue has been resected to clear the view. This may also need to be combined with surface scraping of epithelium when the bullae are severe. All of these techniques can be used and the choice of which one to use depends on the severity of the corneal surface edema and the comfort of the surgeon when working in situations with suboptimal visualization of the anterior segment.

Figure 17-2: Superior limbal peritomy being performed.

Figure 17-3: Scleral tunnel access incision is displayed.

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Figures 17-4A and B: Capsulorhexis is being performed.

We routinely perform a standard “phaco-chop” technique (Figures 17-5A to H) . One aspect that is unique to cataract surgery when combined with DLEK surgery is that the central endothelium is going to be replaced and so the surgeon can be indifferent to its care. The surgeon can bring the entire nucleus up into the anterior chamber for phacoemulsification, if necessary, and not worry about damage to the central endothelium, since the endothelium is going to be replaced by the DLEK portion of the combined procedure. Indeed, Dr. Thomas John has advocated a technique called “Upside-Down Phaco” when combining cataract surgery with DLEK in cases of severe corneal edema. Nonetheless, the surgeon should still respect the integrity and safety of the peripheral endothelium and should perform cataract surgery in the safest possible manner.

We routinely place a foldable acrylic intraocular lens (Figure 17-6) , but the IOL type is based upon surgeon preference. Patients that have significant naturally occurring corneal astigmatism may even have a toric IOL placed for correction, since the small incision DLEK procedure does not seem to significantly induce large

Figure 17-6: Foldable posterior chamber IOL insertion.

Figure 17-7: Removal of Healon from capsular bag.

degrees of astigmatism.14 It is important to remove all of the Healon from the capsular bag (Figure 17-7), and to verify that no Healon is sequestered behind the IOL prior to closing the cataract wound. Any residual Healon left behind after the cataract surgery can have a detrimental effect on the adherence of the donor corneal stroma to the host corneal stroma during the following DLEK procedure. We place a pupil-constricting agent (Miochol acetylcholine chloride solution, Ciba Vision Ophthalmics, Duluth, GA) into the anterior segment to further stabilize the lens, and then close the wound at normal pressure. The cataract wound is selfsealing, but it is reinforced with one or two interrupted 10- 0 nylon sutures. The conjunctiva is then closed with vicryl sutures (Figure 17-8), and attention is directed to the performance of the DLEK surgery from the temporal side.

Recipient Surgery: Small Incision DLEK

Theoperatingmicroscopeisnowpositionedforthesurgeon to be seated at the temporal side of the patient (for small incision DLEK surgery, the scleral access incision is 5 mm, and therefore the incision is usually placed at the temporal

Figure 17-8: Closing the conjunctiva with vicryl sutures.

limbal region rather than superiorly). The patient’s head shouldbepositionedfacingtheceiling,paralleltothefloor. In addition, the endotracheal tube is also positioned by the anesthesiologisttoexitthemouthfromthesideoppositethe surgical field to facilitate the surgeon’s field of movement. A bridal suture can also beplaced beneath thesuperior and inferior recti muscles, if necessary, to aid in the positioning and stabilization of the globe during the DLEK surgery.

A temporal limbal peritomy of the conjunctiva is performed with scissors (Figure 17-9) allowing exposure of about 6 mm arc length (about 3 clock hours) of limbal tissue. Prior to forming the DLEK scleral access incision, two clear corneal limbal stab incisions (about 1 mm diameter) (Figure 17-10) are placed on either side of the peritomy area, 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 chamber to replace the aqueous fully and to maintain normal pressure. We strongly oppose the use of Viscoat (Alcon) or other

Figure 17-9: Temporal limbal peritomy is being performed as the initial step for combined DLEK with phacoemulsification and posterior chamber IOL insertion.

Figure 17-10: Stab incision being performed.

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.

Prior to creating the deep lamellar pocket of DLEK, a template mark is placed on the corneal epithelial surface (Figures 17-11A and B). A circular marker with a diameter of 8.0 or 8.5 mm (depending upon recipient corneal diameter

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Figures 17-11A and B: Template mark on recipient corneal surface.

and surgeon preference) is used to make a circular impression on the central epithelial surface. If the position and centration of the mark is acceptable to the surgeon, then it is accentuated with gentian violet ink marks. This circle on the cornea will later be used as a template for resection of the posterior recipient lamellar tissue.

A trifaceted, guarded diamond knife is then set to a depth of 350 µm and a 5.0 mm length incision is made approximately 1 mm posterior and concentric to the corneal limbus (Figure 17-12). 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 (Figure 17-13) to create a deep sclerocorneal lamellar pocket down to about 75% to 85% corneal depth along the entire length of the wound. Perfect accuracy of the depth of the corneal stromal pocket does not appear to be critical for a good visual outcome.28 Pockets should be deeper than 50% in order to avoid interface scarring or haze, and should not be deeper than 95% depth in order to avoid donor-recipient

Figure 17-12: Diamond knife incision to a depth of 350 µm.

Figure 17-13: Crescent blade being used.

thickness mismatch. 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. Experience with the procedure and with lamellar dissections in general aids in the 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 and then a curved stromal dissector (Devers Dissector, Bausch and Lomb, St. Louis, MO) (Figures 17-14 and 17-15) extends the pocket further. We prefer to have a pocket that extends at least 1 mm peripheral to the diameter of the surface template circular mark (i.e. 10.0 mm pocket diameter for an 8.0 mm mark) (Figure 17-16). This creates a large area of 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

Figure 17-14: Straight Devers dissector is used to initiate the intrastromal corneal pocket.

Figure 17-16: Peripheral Devers dissector being used in the DLEK portion of this triple procedure.

can actually feel the increased resistance to dissection if he 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 desired area of the cornea, in order to allow adequate edge space for the donor disk.

The resection of the posterior recipient tissue begins by first entering the anterior chamber through the temporal scleral corneal pocket incision (Figure 17-17). We utilize a standard cataract surgery diamond blade with a 2.8 mm width, but any blade is acceptable. Entry into the anterior chamber at the exact corresponding position of the temporal edge of the surface template mark is preferred.

It is through this entry point that the recipient posterior resection is started utilizing special scissors designed for

Figure 17-18: Cindy I scissors is being used.

blades that 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. Once the posterior recipient disk has been cut for the full 360° then the tissue is removed from the eye (Figure 17-20) and placed on the corneal surface for inspection (Figure 17-21). It is washed with balanced salt solution (BSS) (Alcon Inc., Fort Worth, TX), and dried with a sponge. The stromal surface is inspected for smoothness and the edges for regularity of the cut, as well as the thickness of the resected tissue. Removal of the recipient posterior edematous stromal tissue, dramatically clears the view into the anterior chamber through the central cornea, and hence, other intraocular surgery such as cataract surgery, vitrectomy, IOL exchange and iridoplasty can be performed at this stage of the DLEK procedure.

After removal of the recipient posterior tissue, the temporal scleral wound is temporarily closed with

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Figures 17-19A and B: Cindy II scissors is used to complete the circular cut.

posterior lamellar tissue resection (Cindy I and Cindy II Scissors, Bausch and Lomb) (Figures 17-18 and 17-19). The Cindy I scissors are placed with one blade in the anterior chamber and one blade in the stromal pocket. The scissors is used to do a free-hand cut, following the marks of the circular template on the overlying epithelial surface. The Cindy I scissors have long, highly curved and low profile

Figure 17-20: Recipient disk removal.

Figure 17-21: Recipient disk inspection.

Figure 17-22: Suturing the wound.

Figure 17-24: Healon is being placed on the donor corneal endothelium.

Figure 17-23: I/A removal of Healon.

1 interrupted 10-0 nylon suture (Figure 17-22). An irrigation/aspiration (I/A) tip is then introduced into the anterior chamber and extensive effort is expended to remove all of the viscoelastic from the eye (Figure 17-23). No Healon should remain in the anterior chamber prior to insertion of the donor disk, otherwise, the donor tissue will not “stick” in place. Therefore, care is taken to irrigate and aspirate the anterior chamber, pupillary area, anterior chamber angle, and even the peripheral pocket as necessary. Once the surgeon is confident that all Healon has been removed, then the pressure of the eye is left slightly soft and attention is turned to preparation of the donor tissue.

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 here in the United States, an artificial anterior chamber (See also Chapter 12, Artificial Anterior Chambers) is necessary for preparation of the donor posterior disk. We utilized a Bausch and Lomb (St. Louis,

MO) artificial anterior chamber that is all stainless steel and has dual irrigation/aspiration ports. The Optisol-GS 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 artificial anterior chamber. The syringe is also attached to the port to be used to vary the intra-chamber pressure 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 17-24). It is then placed endothelial side down onto the post of the artificial anterior chamber (Figures 17-25A and B) 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 corneal surface of the donor tissue and suction is applied. Trephination is carried out to about 60% corneal depth with the trephine. It is noteworthy that after the blade touches the epithelial surface of the donor, it only takes about 4 or 5 quarter turns of the Barron 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% corneal depth should be attained for the plane of the pocket of the donor tissue. Avoid going deeper than 80% corneal depth, since it will usually result in a thin donor corneal disc that will often spontaneously roll up like a rug causing confusion as to which side is the endothelial side and may result in endothelial damage. If the dissection depth of the donor is less than 60% depth, then the stromal surface of the donor corneal disk may not be as smooth and the donor

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Figures 17-25A and B: Donor cornea placement onto artificial anterior chamber.

corneal tissue may be much thicker than the recipient bed is deep. However, whether disparity between donor and recipient disk thicknesses causes a later visual problem is unknown at this time. Similar to the recipient disk preparation, the crescent blade is used to cut down to the 80% depth and it is then extended over the entire area of the cornea, all the way to the limbus, using the straight and curved Devers Dissectors.

As an alternative to beginning the stromal pocket dissection with a measured trephine cut as described above, the surgeon may prefer to simply use a diamond knife (Figure 17-26) set to a depth of 350 µm and make a 3 or 4 clock hour-length incision in the peripheral donor limbal area. The crescent blade is then used to cut to the deeper stromal tissue and then once the desired plane has been reached, then the Devers Dissectors are used as described previously.

After completing the deep stromal pocket formation (Figure 17-27), 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

Figure 17-26: Incision with diamond knife (Barron recipient trephine not used for this patient).

Figure 17-27: Dissection of donor cornea.

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 coating 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 17-28). We utilize a Barron donor punch (Katena). The same size diameter punch is used as the diameter of the circular marker that was used to make the circular impression on the host central epithelial surface. 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 17-29), and if the dissection has been done properly, the surgeon will not hear that familiar “crunch” sound that is so common with full thickness PKP donor trephination. Instead the sound is much quieter or not present at all. While it is best to have a good centration of

Figure 17-28: Donor cornea is placed on the punch block (before punch).

Figure 17-29: Donor cornea on punch block after it has been punched with a trephine blade.

the punch, if the stromal dissection of the donor has been carried out all the way to the limbus for 360°, it will be fine. If the dissection has not been carried all the way out to the limbus, and the surgeon has an eccentric punch, then the posterior donor disk may have a 1 mm thick edge and an opposite 100 µm thick edge. This wedge of tissue will not adhere to the recipient bed, and so care in completion of the total donor stromal pocket is advised prior to punching out the tissue.

Because the 5 mm wound of small incision DLEK surgery is smaller than the 8.0 mm diameter of the donor disk, the donor tissue must be folded prior to insertion. To accomplish this, a very thin strip of Healon is placed onto the endothelial surface (Figure 17-30) along the previously identified and marked horizontal meridian of the donor button. Stabilizing the anterior edge of the donor button with a 0.12 mm forceps, the posterior stromal tissue edge is gently grasped with non-toothed specialized insertion forceps (Charlie forceps, Bausch and Lomb, St. Louis, MO).

Figure 17-30: Thin strip of Healon placed along center of the donor corneal disk.

The posterior tissue is then gently folded with the endothelium on the inside protected by the layer of Healon, and it is folded into an asymmetric “taco” shape, in a 60:40% ratio (Figure 17-31), the most anterior side of the taco being 60% and the posterior side 40%. The donor tissue is then brought over to the operative field still on the trephine block.

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Figures 17-31A and B: Cornea folded over 60/40 taco fold.