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

Figure 23-3: Moria automated lamellar therapeutic keratoplasty unit (Moria, Antony, France) with a donor cornea that is mounted within the artificial anterior chamber (AAC). The AAC is filled with Optisol GS, and a CB microkeratome is mounted on the post and ready for use. The ALTK unit is attached to a 10.0 ml sterile syringe that is partially filled with the Optisol GS solution and it is connected to the ALTK unit by a short sterile tubing via a valve unit.

(Figure 23-3). The syringe plunger is depressed to increase the intrachamber pressure that is confirmed by finger palpation and the valve is turned to the locked position. I routinely use finger palpation at this stage, however, if one prefers a Barraquer tonometer it may be used.

Remove the epithelium with a Meracel sponge (Figure 23-4) and mark the center of the cornea with a dot and a radial mark at the corneal periphery with a sterile surgical marker for reference points. Removal of the corneal epithelium (Figure 23-4) gives an additional 50 micron deeper cut with the microkeratome. Moria makes different microkeratome heads. I prefer to use a 300-micron head on all my donor corneas for DSAEK procedures. When using a 300-micron head (Figure 23-5), I am of the opinion there is no need to take pachymetry readings on any of the donor corneas (personal experience). However, if a surgeon uses 350 micron head then pachymetry is usually a must to prevent inadvertent corneal perforation in some cases. Check the microkeratome after inserting a new blade into the blade slot, and also make sure there are no blade edge defects. Use sterile balanced salt solution to moisten both

Figure 23-5: Photograph of a 300 micron Moria microkeratome head for the DSAEK procedure.

the microkeratome head in the region of the blade and on the donor corneal surface prior to cutting the cornea.

Surgical Pearl: Just before cutting the donor cornea re-tighten the ring in the Moria ALTK unit, as this will ensure good holding of

Figure 23-6: Upper left – Donor cornea being cut using a Moria ALTK system; Main Figure – A free-cap of the donor cornea is seen within a Moria 300 micron head.

Ophthalmics, USA) is then placed on the cut corneal surface to bathe the surface, thus staining only the cut stromal surface (Figure 23-7) (See also Chapter 32, Use of Dyes in DSAEK and DLEK). The adjacent uncut cornea with its intact epithelium does not stain. The excess Vision Blue is removed using a sterile Merocel® eye spears (Figure 23-7) (Medtronic Ophthalmics, Jacksonville, FL). It is essential not to introduce any debris on the corneal surface at this stage, since it can subsequently get trapped within the donor-host interface and be present postoperatively. The free cap is replaced (Figure 23-8) and aligned using the

pre-placed markings (Figure 23-9). The outer ring in the Moria ALTK unit is rotated to the unlocked position.

Surgical Pearl: Do not pull the outer sleeve immediately from the unlocked position, since the cornea can collapse inwards and the endothelium can contact the metal surface of the central post and result in endothelial cell loss. I recommend that the outer sleeve and cornea be raised hydraulically by pressing on the plunger after almost completely filling the syringe with Optisol GS solution. If the cornea collapses inwards during his step it will not hit the metal surface. Once the outer sleeve is raised it can be removed from the ALTK system and the cornea is

removed using a 0.12 forceps and placed on a corneal punch with the epithelial side down (Figure 23-10). Using a Moria Hanna Punch trephination is carried out from the endothelial side after suction keeps the cornea in place (Figure 23-10). This is a “2 unit” cornea with a free anterior cap and the posterior stroma and endothelium. Avoid lateral displacement of the “2 units” of the cornea. Use the area of trypan blue staining as a guide to trephination such that the circular blade cuts within the blue stained region to prevent eccentric trephination (Figure 23-10). Figure 23-11 shows an example of trypan blue stained and unstained corneas. The blue staining helps in DSAEK procedure both in the donor corneal preparation and within the anterior chamber of the recipient.

Step 3: Host Cornea

The preferred anesthesia is topical anesthesia using 2% lidocaine jelly with monitored anesthesia care (MAC), whether it is a primary procedure, or a secondary disk exchange procedure (Figure 23-12). Complete hemostasis is essential before entering the anterior chamber via the temporal wound (Figure 23-13). Surgical Pearl: Take the

additional time for complete hemostasis to prevent donorrecipient interface entrapment of blood. Any blood in the interface will decrease vision postoperatively and result in potential interface inflammation, depending on the location and amount of the entrapped blood. The preferred wound size is 5.0 mm (Figure 23-14) to minimize endothelial cell damage. The limbal wound depth is 350 microns (Figure 23-15). An intra corneal pocket is constructed via the temporal wound (Figure 23-16). The anterior chamber is not entered at this time.

The anterior chamber is entered both to the right and left of the temporal wound using a 15-degree super blade (Alcon Inc., Fort Worth, TX). Surgical Pearl: Removal of the Descemet’s membrane under fluid (Figures 23-17 and 23-18) is much more difficult than under viscoelastic such as Healon. Always use a cohesive viscoelastic such as Healon (Figure 2319) at this stage of the surgery and it will simplify DSAEK surgery significantly as compared to working under fluid. The use of Healon does not jeopardize the donor disk adherence to the recipient cornea since this Healon will be removed (see below).

With Healon filling the anterior chamber, Descemetorhexis and removal of the Desecemet’s membrane as a single disk is carried out using the John Dexatome (ASICO Inc.,

Westmont, IL) (Figures 23-20 and 23-21). Surgical Pearl: Always touch the folded Descemet’s membrane and not the stromal surface. This will result in the best possible recipient side of the interface and thus may contribute to improved vision postoperatively. John Dexatome (ASICO Inc., Westmont, IL) will permit removal of the Descemet’s membrane as a single disk every time without the use of a second instrument. Remain in the same plane when removing the Descemet’s membrane without entering into the stroma. The unique curvature design of the

John Dexatome permits easy access to any part of the inner dome of the recipient cornea. Removing the Descemet’s membrane as a single disk (Figure 23-22) is essential so that re-entry into the anterior chamber is not necessary to remove Descemet membrane tags and remnants. Descemetorhexis is begun in the distal point from the anterior chamber entry site and it is continued first in a clockwise direction (Figure 23-23) and then starting again from the distal starting point it is continued in a counter-

Figure 23-13: Complete hemostasis is essential before entering the anterior chamber via the temporal wound.

Figure 23-14: Preparation of the temporal region of the patient’s eye. A circular mark is placed on the corneal epithelium of the chosen diameter. A Castroviejo caliper is set at 5.0 mm to mark the limit of the limbal wound.

Figure 23-15: The limbal wound depth is 350 microns.

clockwise direction to complete the 360-degrees (Figure 23-24). While detaching the Descemet’s membrane both the leading and the trailing edges need to be watched so that the Descemet’s membrane is removed as a single disk every time (Figures 23-25 to 23-28). The Descemetorhexis is performed about 0.5 mm within the epithelial mark. Since the donor disk has the same diameter as the epithelial mark, the disk overlaps the peripheral 0.5 mm area and prevents any break through corneal edema. When performing this

step in a failed PKP cornea, the PKP wound is used as the circular guide and no epithelial mark is made in these cases. The fully detached Descemet’s membrane is removed from the anterior chamber after entering the anterior chamber through the previously made limbal wound in the temporal region (Figures 23-14 to 23-16) using a 3.2 mm keratome blade.

The peripheral stroma within the epithelial circular mark is made rough by using the John DSAEK scrubber (ASICO Inc., Westmont, IL) to enhance donor disk attachment to the recipient cornea (First described by Terry, M). This is completed 360-degrees, first in a clockwise direction, followed by a counter-clockwise direction (Figure 23-29). Complete removal of Healon from the anterior chamber using an irrigation/aspiration unit is essential for donor corneal disk adherence to the recipient corneal stroma (Figure 23-30). Peripheral iridectomy is not performed during DSAEK surgery since this can result in intraoperative bleeding.

The donor corneal disk is folded into a “taco-fold” after placing a small amount of Healon on the endothelial surface (Figure 23-31). Donor corneal disk is placed in the recipient anterior chamber after enlarging the entry wound to 5.0 mm. The wound is then closed with three interrupted

10-0 nylon sutures (Figure 23-32). The donor disk is unfolded using filtered-air (Figure 23-33). The air is injected in a steady, controlled fashion. Donor disk is uniformly adherent to the patient’s cornea and it is well centered. Also seen is the double-ring sign (Figure 23-34). “Fork-lift” taco helps in initial stroma to stroma adherence and facilitates unfolding of the taco. The cannula is placed between the folded taco and the anterior iris surface and sterile balanced salt solution is injected to gently lift the taco (Figure 23-35).

The taco fold is usually a 60/40 fold. This may be done as an over-fold or more recently an under fold in which case the hand is rotated for proper orientation while inserting the taco into the anterior chamber. In some cases the taco fold may be 70/30 or occasionally an 80/20 fold. However, as one moves away from the 60/40 towards 80/20 there is more endothelial cell exposure and hence potentially increased cell damage. A large air bubble facilitates adherence. Wait 8 to 10 minutes with an air-filled anterior chamber to facilitate initial disk adherence. The air bubble size is then decreased by airfluid exchange.

In some patients with a deep anterior chamber, fluid unfolding of the donor disk may be possible (Figure 23-36). If the donor disk begins to unfold in the wrong direction then the John Fixation Hook (ASICO Inc., Westmont, IL) may be used to pin the donor disk against the recipient cornea, followed by air-unfolding of the donor disk (Figures 23-37 to 23-39). Following air attachment of the donor corneal disk, if there are macrofolds in the donor disk, then the Lindstrom roller or the John DSAEK Glider (ASICO Inc., Westmont, IL) may be used to decrease or eliminate the folds (Figure 23-40). Figure 23-41 shows the presence and absence of macrofolds in the donor corneal disk. There are different insertion techniques to place the donor corneal disk within the recipient anterior chamber (Figures 23-42 to 23-46). These are either “push” or “pull” –through techniques (Figure 23-42).

Residual air bubble is usually seen 1 day following DSAEK procedure (Figure 23-47). Howeevr, the air bubble partially or fully clears the pupillary diameter and hence there usually is no risk of acute pupillary block glaucoma attack on or after day 1 following DSAEK surgery. There often is relatively rapid clearing of the corneal edema