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Ten pearls to assist DMEK surgery
DMEK may become the preferred procedure for surgical correction of endothelial decompensation.
Corneal transplantation for endothelial decompensation with blurred vision continues to evolve from penetrating keratoplasty to Descemet’s stripping automated endothelial keratoplasty to Descemet’s membrane endothelial keratoplasty. Each of the new surgical techniques improves the quality of vision and speeds visual recovery without full-thickness corneal wound, induced corneal astigmatism and corneal sutures associated with PK. Additionally, the rate of corneal graft rejection is lower with DMEK than with DSAEK or PK. Most patients who undergo DSAEK in one eye and DMEK in the other seem to prefer the eye with DMEK to the DSAEK eye. This is often associated with a better quality of vision and fewer higher-order aberrations with DMEK. The near normal corneal anatomy is restored, while with DSAEK there is an increase in overall corneal thickness. DMEK also provides more 20/20 eyes than DSAEK. Hence, DMEK may become the preferred procedure for surgical correction of endothelial decompensation.
In this column, I describe 10 surgical pearls to assist in DMEK.
Improve visualization
During DMEK surgery, the view of the anterior segment is often compromised due to the endothelial decompensation and corneal edema. If the edema is mild to moderate and there is adequate visualization of the anterior chamber, DMEK can be carried out through an intact epithelium (Figure 1). However, if there is significant edema of the corneal stroma and the epithelium with significant degradation of the anterior chamber view, then removal of the corneal epithelium will usually augment the view and facilitate the procedure. In these instances, the edematous epithelium may be removed using a Weck-Cel spear and smooth-tipped forceps. The circular mark can then be placed on the corneal surface (Bowman’s layer) to act as a guide during descemetorhexis on the patient’s cornea. Figure 1 is a case of pseudophakic endothelial decompensation due to an anterior chamber IOL. Performing DMEK with a space-occupying IOL can be difficult and should not be an early case during the learning curve.
Multiple access wounds
Create multiple access wounds into the anterior chamber in the peripheral cornea close to the limbus using a 15° super blade. These wounds can be highlighted using a sterile marking pen for easy identification. These wounds may then be used to introduce a blunt 30-gauge cannula to inject sterile balanced salt solution to assist in the unfolding of the donor Descemet’s membrane within the recipient anterior chamber. These wounds usually self-seal and often do not require suture closure. Using one of the entry wounds, Healon (sodium hyaluronate, Abbott Medical Optics) is injected into the anterior chamber, and careful descemetorhexis is performed using the John Dexatome spatula (Mastel) (Figure 2). The curvature of the Dexatome facilitates Descemet’s membrane removal in all DMEK procedures, especially in a reduced-volume anterior chamber due to the anterior chamber IOL. Descemet’s membrane is removed as a single circular disc.
Figure 1. Slit lamp photograph displaying corneal stromal and epithelial edema with irregular light reflex and an anterior chamber IOL.
Images: John T
Figure 2. Careful descemetorhexis is performed using the John Dexatome spatula without damaging the anterior chamber IOL or the iris tissue. Insert: The Descemet’s membrane is removed as a single circular disc.
Figure 3. Before performing DMEK, an anterior synechiolysis is performed to lyse iris adhesions to the recipient inner corneal surface and reform the anterior chamber. Such a maneuver restores additional anterior chamber volume and helps in the unfolding of the donor Descemet’s membrane without the donor tissue getting entangled in the region of the shallow anterior chamber with iris adhesions. Right: Completed view of the anterior synechiolysis.
Compromised AC space
Recognize cases with compromised anterior chamber space due to iris adhesions to the cornea, namely peripheral anterior synechiae. Such adhesions should be lysed before placing the donor Descemet’s membrane into the anterior chamber (Figure 3).
Combined DMEK and phaco
When performing a DMEK triple procedure — DMEK with cataract extraction and a posterior chamber IOL — consider doing an upside-down phaco technique within the anterior chamber (Figure 4). Endothelial cell damage in this case is not an issue because the recipient endothelium is replaced with healthy donor endothelium. This technique requires a larger capsulorrhexis to facilitate delivery of the cataractous lens out of the capsular bag. The nucleus is flipped into the anterior chamber using the same cannula that was used for the hydrodissection. This is done in one smooth continuous maneuver such that the posterior lens surface faces the endothelial surface of the recipient cornea. Healon is injected into the capsular bag to push the capsule away and prevent any accidental tears during phacoemulsification. The phaco tip is then placed in between the iris surface and the anterior lens surface (lens in the flipped position), and phacoemulsification is carried out in this upside-down fashion. As the lenticular groove proceeds toward the posterior lens surface, the lens splits in two without the use of a second instrument, much like splitting a log of wood with a metallic wedge. The lens is then rotated, and similar maneuver further splits the lens into smaller segments for easier emulsification. This procedure is considered safe because the phaco tip is further away from the posterior lens capsule than when performing phacoemulsification in the posterior chamber through a cloudy cornea.
Figure 4. Schematic representation of upside-down phacoemulsification (John technique).
Figure 5. Donor Descemet’s membrane is peeled under fluid, taking care to prevent any Descemet’s membrane tears.
Constrict the pupil
Constrict the pupil after descemetorhexis and removal of the recipient disc of Descemet’s membrane. This decreases the chance of the donor tissue disappearing into the posterior chamber through the pupil.
Small inferior peripheral iridectomy
Perform an inferior peripheral iridectomy to prevent acute postop glaucoma.
Donor tissue preparation
Detach the donor Descemet’s membrane slowly under fluid while watching the periphery of the Descemet’s membrane (Figure 5) to prevent any potential tears.
Stain donor Descemet’s membrane
Staining the donor Descemet’s membrane with Vision Blue (trypan blue, DORC) facilitates visualization of the donor tissue within the recipient anterior chamber (Figure 6). Such staining can also help in the identification of the endothelial surface of the donor tissue.
Figure 6. After introduction of the trypan blue-stained donor Descemet’s membrane into the recipient anterior chamber, close the temporal clear corneal wound with a single 10-0 nylon suture to retain the Descemet’s membrane within the recipient anterior chamber, especially during the next surgical step of unfolding the donor Descemet’s membrane.
Figure 7. John Smoother instrument is used to unfold and center the donor Descemet’s membrane without using any air bubble during unfolding. Avoiding air in the anterior chamber when unfolding Descemet’s membrane is useful in all DMEK procedures and especially helpful in this eye with an anterior chamber IOL.
Close corneal wound
After introducing the rolled-up donor Descemet’s membrane with its healthy endothelium on the outside surface, close the temporal clear cornea wound with a 10-0 nylon suture (Figure 6). This should be done before any further manipulations or surgical maneuvers are made within the eye. Do not inject fluid such as sterile balanced salt solution into the anterior chamber with an open corneal wound, which could result in ejecting the donor disc outside the eye onto the sterile drapes and cause potentially significant endothelial cell loss.
Unfold donor Descemet’s membrane
The donor Descemet’s membrane is usually unfolded with the assistance of a small air bubble between the iris and the donor tissue. However, the use of the John Smoother instrument (Bausch + Lomb) helps unfold the donor tissue without use of an air bubble (Figure 7). This instrument also helps center the donor tissue to correspond with the circular mark on the corneal surface. The unfolded tissue is then attached with an air bubble. It is important to ascertain that the cannula tip is in proper position, in this case between the anterior chamber IOL and the donor Descemet’s membrane, before injecting air. Air injection should be performed in a gradual and steady manner to avoid dislodging the donor Descemet’s membrane. Use of intraoperative slit lamp assists in confirming uniform attachment and ascertaining that there is no fluid, air or debris in the donor-recipient interface.