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Optimizing pre-Descemet endothelial keratoplasty technique

Ross, Andrew R. MD, PhD; Said, Dalia G. MD, FRCS; Colabelli Gisoldi, Rossella A. M. MD; Nubile, Mario MD, PhD; El-Amin, Abdalla MD, PhD; Gabr, Ahmed F. MD, PhD; Abd Ed-Moniem, Mohamed MD, PhD; Mencucci, Rita MD; Pocobelli, Augusto MD; Mastropasqua, Leonardo MD; Dua, Harminder S. CBE, MD, FRCOphth, PhD

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Journal of Cataract & Refractive Surgery: May 2020 - Volume 46 - Issue 5 - p 667-674
doi: 10.1097/j.jcrs.0000000000000157
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Abstract

Endothelial keratoplasty is one of the most important recent advances in modern ophthalmology.1 Its aim is to replace the diseased corneal endothelium. Multiple techniques of endothelial keratoplasty are described, including Descemet-stripping endothelial keratoplasty (DSEK) in which the endothelium together with the Descemet membrane and a thin layer of the posterior stroma are transplanted to replace the diseased endothelium. This can be performed either manually by DSEK or by Descemet-stripping automated endothelial keratoplasty (DSAEK). Descemet membrane endothelial keratoplasty (DMEK) is the only procedure that offers anatomical replacement of the diseased tissue wherein the Descemet membrane and the endothelium are transplanted. Although DMEK has statistically significant superior visual acuity results, it has many challenges and a steep learning curve.2–4 Challenges include an increased incidence of loss of tissue during preparation, difficulty in unrolling and correct orientation of the donor tissue scroll intraoperatively with associated endothelial cell loss, higher incidence of posterior synechiae formation, relatively high rebubbling rate, trickier tissue to rebubble, and difficulty in preparing tissue from younger donors.3–8 Although DSEK shows lower rejection rates compared with penetrating keratoplasty, it is still an issue, occurring in 8% of cases at 1 year and 12% at 2 years. DMEK tissue has a significantly reduced risk for graft rejection compared with DSEK with a rate of 1% at 1 year and 2 years.9 Although overall DSEK rejection rates are comparatively higher than DMEK, Madi et al. have recently demonstrated a reduced graft rejection rate with ultra-thin (UT) DSAEK with Kaplan–Meier cumulative probability of a rejection episode of 3.4% and 4.3% at 1 and 2 years, respectively.10 Hence, when reporting endothelial keratoplasty rejection rates, one should distinguish between DSEK, UT-DSAEK, and DMEK.

The pre-Descemet layer (PDL), or Dua layer (also termed the Dua-Fine layer by the American Association of Ocular Oncologists and Pathologists), is around 15 to 20 μm thick and is composed of 5 to 8 lamellae of compact collagen (types III, IV, and VI).11,12 It was initially suggested and subsequently demonstrated that the composite of the PDL with the Descemet membrane and endothelium could be used for endothelial keratoplasty in a technique termed pre-Descemet endothelial keratoplasty (PDEK).12,13 This offers the advantages of less tight scrolling and ease of handling and unscrolling in the eye, and can be harvested from donors of any age.14 The thin layer of the PDL, approximately 15 to 20 μm thick, composed predominantly of elastin and collagen that is associated with PDEK donor tissue, is essentially devoid of cells.15,16

The surgical technique for PDEK is still in evolution, and different steps are used by different surgeons. We report here a standardized technique with the aim of making the procedure more consistent, to minimize the steepness of the learning curve, and to improve outcomes.

SURGICAL TECHNIQUE

Patient Selection

Patients with corneal endothelial failure and persistent corneal edema (eg, Fuchs endothelial dystrophy, failed penetrating grafts, and pseudophakic bullous keratopathy) without stromal scars are suitable candidates for this procedure. As with DMEK, eyes with aphakia, large fixed pupils, glaucoma filtering devices (tube shunts), and extremes of refractive error should be avoided by beginners. However, surgeons adept in DMEK will find PDEK relatively easy to perform.

Anesthesia

The procedure can be performed under sub-Tenon, peribulbar, or retrobulbar block and general anesthesia. The amount of anesthetic injected in the orbit is important, as it can cause compression of the eye and shallowing of the anterior chamber (AC) if excessive. Equally, adequate injection can displace a sunken eyeball anteriorly, facilitating ease of access.

PDEK Tissue Preparation With the PDEK Clamp

Centration

Centration is a crucial step in the preparation to ensure appropriate application of the PDEK clamp to prevent escape of the injected air from the tissue and prevent the formation of a type 2 big bubble. This can be achieved subjectively by ensuring that an equal amount of corneal tissue is seen outside the clamp around its circumference (Figure 1, A). Alternatively, 2 pairs of dots, opposite to each other, in 2 meridians at right angles to each other, 2.0 mm from the limbus, are marked with ink on the epithelial surface (Figure 1, B). These help with centration during clamping.

Figure 1.
Figure 1.:
PDEK graft preparation. A: The scleral–corneal disc is placed in a PDEK clamp. Graft centration is achieved by ensuring that an equal amount of corneal tissue is seen outside the clamp around its circumference. B: Graft centration can be ensured by placement of 2 pairs of dots, opposite to each other, in 2 meridians at right angles to each other, 2.0 mm from the limbus on the epithelial surface. C: The 4 dots (arrows) are seen within the inner circumference of the ring at equal distance from the edge of the ring confirming graft centration. D and E: Mixed big-bubble formation due to failure of centration of the scleral–corneal disc. Unequal distance of the compressed corneal tissue can be seen around the area of stromal emphysema. F: The needle is advanced intrastromally to the paracentral region of the corneal tissue for approximately 4.0 mm. The needle should be visualized in 1 plane through its insertion to avoid inadvertent perforation. G: To achieve the maximum size of the big bubble, the needle tip (arrow) can be carefully introduced into the bubble and cautiously inject a little more air (PDEK = pre-Descemet endothelial keratoplasty).

Clamping

The PDEK clamp is then applied.17,18 The PDEK clamp (e.janach, Italy) has a spring handle ending in 2 rings. Both rings have an internal and external diameter of 9.0 mm and 11 mm, respectively. The handle has a screw, which can be tightened to maintain the clamp in the closed position. Each ring has an indentation, which, when opposed, form a hole through which a 27- or 30-gauge needle can be passed. Two versions of PDEK clamp are available: one for right-handed and the other for left-handed surgeons. The screw on the clamp handle is loosened to the maximum possible. This allows maximum separation of the 2 rings of the clamp. The marked sclera–corneal disc is held with toothed forceps by the scleral rim and placed between the rings, resting on the lower/outer ring with the endothelial surface facing the surgeon. Centration is confirmed by ascertaining that the 4 dots are visible within the inner circumference of the ring at equal distance from the edge of the ring (Figure 1, C). While holding the scleral–corneal ring with toothed forceps to prevent displacement, the upper ring is gently clamped on to the tissue, ensuring that the 4 dots continue to be visualized within the ring. The screw is tightened to affix the tissue between the rings. Failure of centration can result in escape of air during injection, the formation of a type 2 (air between the PDL and the Descemet membrane) or mixed bubble (types 1 and 2) (Figure 1, D and E), which will yield DMEK tissue instead of PDEK tissue.

Air Injection

Filtered air is drawn into a 1, 3, or 5 mL (surgeon's preference) Luer-lock syringe. A 30-gauge needle is connected to the syringe and is bent at mid length to an angle of approximately 135°, bevel up. The tip of the needle is inserted into the scleral rim directly under the indicator mark on the inner ring, which is a guide to the position of the hole in the clamped rings. The needle is advanced intrastromally to the paracentral region of the corneal tissue for approximately 4.0 mm (Figure 1, F). The needle tip should be visualized throughout this step to maintain a constant midstromal plane to avoid corneal perforation in either direction. The plunger of the syringe is then slowly pushed to force air into the stroma. Air is injected in a continuous manner until a type 1 big bubble appears. At this point, pressure on the plunger is eased but maintained with less force as the big bubble continues to expand. Once a big bubble of reasonable size is obtained, the pressure on the plunger is released, the syringe held like a pen between the thumb and the forefinger, and the needle is manipulated to enter the big bubble (Figure 1, G). Very gentle intermittent pressure is applied to the plunger, which allows the bubble to expand a little further. The needle is withdrawn, the screw loosened to its full extent to separate the rings, and the scleral–corneal tissue with the big bubble is gently removed avoiding touch with the upper ring of the clamp.

Based on the above description, a type 1 big bubble was obtained in all 20 scleral–corneal discs tested. The size of a type 1 big bubble measured with a Castroviejo caliper (Altomed) was 7.255 ± 0.535 and 6.745 ± 0.668 mm in the longest and shortest meridians, respectively.

Dissection of PDEK Tissue

A few drops of trypan blue (Vision Blue; DORC) are gently placed on the bubble to completely cover it. PDEK tissue can be dissected from the scleral–corneal disc either by trephination or by manual excision with a pair of scissors. For trephination, the bubble size is measured with a caliper, and a slightly smaller sized manual trephine is used (6.0 to 7.0 mm). Air is aspirated from the bubble with the same needle inserted into it from the scleral rim to flatten the bubble. The trephine is centered on the PDEK tissue and pressed on the tissue to make a circumferential cut. It is not necessary to punch through the full thickness of the underlying stroma. Usually, the circumference is not completely incised because of the variable nature of the shape of the big bubble at its attachment to the stroma, and small attachment(s) along the circumference that need to be cut with a pair of fine Vannas scissors. For manual excision with scissors, the big bubble is pierced with a sharp 15° super blade (Mani, Inc) at the attachment of the bubble wall to the cornea. The knife is moved in a sawing motion to enlarge the incision to 2.0 to 3.0 mm. Trypan blue is injected into the bubble without trying to force the air out. The air under the PDEK tissue props the tissue allowing ease of excision. If air is lost, more can be injected. The PDEK tissue is cut along the circumference of the bubble rotating the tissue between cuts to adequately align the blade of the scissors with the site to be cut. Straight narrow Vannas scissors are preferred over a curved tip one, as the latter is likely to make tiny notches in the tissue to be transplanted. Thin strands of tissue may at times be seen to stretch between the deep stroma and the anterior surface of PDEK tissue. These need to be cut to ensure that the PDEK tissue is completely separated from the stroma.

Folding

PDEK tissue scrolls like DMEK tissue with the endothelial cells on the outside.15 By submerging the tissue in balanced salt solution and gentle shaking, it can be made to form a scroll, which can be mounted in an appropriate injector for transfer into the AC. Alternatively, after removing the fluid around the tissue with the help of an absorbent Weck-Cel cellulose eye spear (BVI, Waltham, MA, USA), the tissue can be folded, endothelial surface inside, by holding the edge on one side and folding one third on itself and then holding the other side to overlap the first fold. An “S” or “F” mark can be made on the stromal surface with an inked Sinskey hook (DTR Medical) or a customized “F” or “S” marker (e.janach, Italy). This can be performed by drying the stromal surface of the folded tissue and placing the mark directly on it. The folded tissue is kept moist and stained with trypan blue for 3 minutes before insertion. Alternatively, as described for DMEK, after folding the PDEK tissue to just over half its diameter, a 3.0 mm hole can be punched in the underlying stroma with a skin biopsy punch (Stiefel) and the PDEK tissue reflected back to lie on the stroma. The scleral–corneal disc is then turned around such that the epithelial surface faces the surgeon, the anterior surface of the PDEK tissue in the stromal hole is dried by absorbing moisture with a Weck-Cel cellulose eye spear, and the “F” or “S” mark placed on it.

Wound Creation

The principle of the surgical insertion site wound is the same as that made for phacoemulsification or DEMK. The wound is a peripheral self-sealing clear corneal tunnel. A keratome (Mani) is used to create a 2.2 mm wide incision of approximately 1.0 mm length from the epithelial to endothelial surface in a triplanar fashion. The main wound can be superior or temporal, determined by surgeon preference. Two corresponding side ports with an MVR 20 blade (Mani) are also made.

Recipient Descemet Membrane Removal

The recipient Descemet membrane and the endothelium are scored with a reverse Sinskey hook (DORC), 0.25 mm larger than the obtained graft size, and the Descemet membrane is removed with a posterior lamellar keratoplasty scraper (DORC). Use of trypan blue helps visualize the Descemet membrane and enables identification of any residual fragments that may remain attached. If descemetorhexis is not complete, tags of the Descemet membrane can remain along the circumference. These should be removed by grasping with forceps and stripped as they can interfere with attachment of graft. Alternatively, they can be sucked into the port of an aspiration cannula and peeled off. Free fragments that remain attached to the posterior stroma (recipient PDL) too can be removed by aspiration. Instead of trypan blue, a large bubble of air in the AC enhances contrast and enables visualization of the edges of residual fragments and tags.

Insertion of PDEK Tissue

Injection Technique

The insertion technique for both, the scroll or trifold preparation of the PDEK donor tissue, is essentially the same with a slight variation during staining and in relation to orientation of the tissue during injection into the AC. For inserting the PDEK scroll or trifold, the graft is loaded into a standard intraocular lens injector cartridge (Medicel), but any endothelial keratoplasty injector will be suitable. The spring from the spring-loaded plunger is removed from the plunger thus: The plunger is pushed forward, the blue cap at the tip is held with blunt forceps and removed, the spring is held with toothed forceps and pulled out, and the cap refitted on the tip. For scroll formation, the donor tissue, while still in the concavity of the scleral–corneal button, is stained with trypan blue by placing a few drops on it to completely cover it for 3 minutes. The tissue is then flooded with a balanced salt solution to wash off the trypan blue, and the container (Petri dish or galley pot) with the tissue is gently shaken from side to side to allow the tissue to scroll, preferably in a double scroll. The nozzle and the open lower groove of the cartridge are filled with a balanced salt solution, and the scrolled tissue loaded into the groove. By gently nudging the floating scroll, it is pushed into the nozzle of the injector. It can also be held at the edge and pulled into the groove. The tissue is oriented such that the open length of the double scroll or the visible edge of the single scroll are away from the bottom of the lower groove (will face the upper groove when the cartridge is closed) (Figure 2, A and B). For the trifold preparation, the folded tissue is stained as above, but excess stain is diluted by adding a few more drops of a balanced salt solution. Excess balanced salt solution could cause it to open. The folded tissue is held with smooth-tipped forceps at one end such that the 2 overlapping folded thirds and the tissue beneath are all held together (Figure 2, C). The tissue is then placed in the lower groove of the cartridge such that the folded thirds face the bottom of the groove (Figure 2, D).

Figure 2.
Figure 2.:
PDEK graft loading. A, PDEK tissue forming a double scroll. The tissue is stained with trypan blue, and the endothelium (dark blue) is on the outside of each scroll. B: PDEK tissue forming a single scroll. The tissue is stained with trypan blue, and the endothelium (dark blue) is on the outside. C: Trifold preparation of PDEK tissue stained with trypan blue. The red star represents the area where the 2 overlapping folded thirds can be held together with smooth-tipped forceps. D: Trifold PDEK placed in the lower groove of the cartridge such that the folded thirds face the bottom of the groove; light blue color represents the Descemet membrane (PDEK = Pre-Descemet endothelial keratoplasty).

The tissue is then nudged into the nozzle of the cartridge by pushing from behind. Hereafter, for both types, scroll or trifold, the groove is filled with a balanced salt solution, and the cartridge is closed. To avoid trapping air bubble(s), this maneuver should be performed under a balanced salt solution. The cartridge is then loaded in the plunger unit, and while blocking the bevel tip of the cartridge with a fingertip, the cylinder of the injector unit behind the cartridge is filled with a balanced salt solution and the plunger advanced into the back of the nozzle. This too can be performed under a balanced salt solution to avoid pushing air into the nozzle. Any air at the tip of the nozzle can be expressed by gently moving the plunger forward. As there is no spring, it will stay in the position at which it is left. It is important that no air is trapped in the nozzle. During injection, air invariably moves forward faster than the fluid and can flatten the tissue against the wall of the nozzle. When ready to insert the tissue in the eye, the position of the bevel in relation to the open length of a double scroll, the edge of a single scroll, or folded flaps of the trifold is noted. The nozzle is rotated such that the open length of a double scroll or the visible edge of a single scroll faces upwards, or the folded flaps of the trifold face downward (Figure 2, B).

The AC should be reasonably filled with a balanced salt solution during injection. This can be performed by maintaining a gentle flow through an AC maintainer or injection of a balanced salt solution through a side port. If the tissue touches the iris during injection, it tends to wrinkle or crumple. Once fully injected into the AC, the irrigation is turned off before removing the injector nozzle. External pressure is applied on the wound to keep the lips apposed, avoiding expulsion of the tissue with the fluid that invariably escapes during withdrawal of the nozzle. The AC is flattened by expressing fluid from a side port before releasing pressure on the main wound and placing a suture to close it.

As an alternative to injection (pushing from behind), the PDEK tissue can be pulled into the AC with forceps. This requires a side port to be made opposite the main wound through which Busin forceps (Moria Antony France) are introduced to grasp the tissue at the tip of the injector nozzle. The tissue is pulled in and allowed to unfold.

PDEK Graft Unfolding

Unfolding techniques used for DMEK tissue apply equally to PDEK tissue. The PDEK tissue scrolls less than DMEK tissue, thus unfolds much easier.15 Graft unfolding is assisted by tapping on the epithelium from outside. A very shallow but not a flat AC is essential. Central tapping forces fluid between the folds, pushing them outwards and opening the folds; while the close proximation of the posterior cornea to the iris holds the unfolding/unfolded lips of the tissue in place without recoiling, until repeated tapping fully opens the tissue. Graft orientation is confirmed by the “F” or “S” mark or position of the scroll and direction of unfolding by tapping or other maneuver, ensuring that the outside of the scroll remains posteriorly directed (for scrolled tissue) or the other way round for trifold tissue. If orientation is not correct, the AC is irrigated with a balanced salt solution, and by using the flow and internal currents created, the graft is flipped in the AC to the desired orientation, and the unfolding maneuver repeated. If visualization is difficult because of corneal edema, the epithelium can be removed, and an endoilluminator can be used from outside, directed into the AC from the limbus, to help visualization of the graft in the AC.19 In difficult cases in which the blue color of dye is diluted out and visualization becomes difficult, the PDEK tissue can be restained by injecting trypan blue dye in the AC and retaining it for a minute before gently washing it out.

Graft Centration and Tamponade

The flat unfolded PDEK tissue (edges may be slightly curled anteriorly) centered over the pupil by tapping. If considerably decentered, a blunt spatula can be used to stroke the stromal surface of the PDEK tissue in the AC in the desired direction. Once centered, if a wrinkle is seen in the tissue, it can be ironed out by further gentle tapping. Once the graft is centered, a Rycroft cannula (Sterimedix) attached to a 2 mL syringe filled with air is passed through a side port, between the donor tissue and the iris, gently sliding it along the iris avoiding touch to the endothelial surface of the graft. When the tip of the cannula is in the pupil center, air is slowly injected to lift the graft and appose it lightly against the posterior corneal surface. Two tips can be helpful here: (1) Before injection of air, the plunger in the syringe should be moved back and forth a few times to make the movement smooth. The initial inertia of the plunger in the barrel may require extra force to get the plunger to move with sudden egress of excessive air in the AC. (2) If the tip of the cannula is paracentral at the time of air injection, the tissue is lifted from one side toward the other, which can cause it to decenter. After obtaining a partial fill with air, if the tissue is not in the desired position, it can be stroked with a blunt spatula inserted between the posterior corneal surface and the stromal surface of the tissue. More air is injected to completely fill the AC, and the eye is firm. This is maintained for 10 minutes, and some air is removed by gentle pressure on the inferior lip of one of the side ports such that the eye is not hard. Twenty percent SF6 in air can be used instead. If air leakage through any of the ports becomes an issue, the lips can be hydrated or wound closed with a single 10-0 nylon suture, and air injected with a 30-gauge needle inserted directly into the AC through the limbus and the needle rapidly withdrawn while continuing to inject air.

Inferior Peripheral Iridotomy/Iridectomy

An inferior peripheral opening in the iris is an insurance against pupil block glaucoma. This should preferably be performed by YAG laser prior to day of surgery. It can also be performed surgically at the time of surgery but carries the risk for bleeding and fibrin in the AC, which can make graft manipulation in the AC difficult. The PDEK technique is illustrated in Video 1 (Supplemental Digital Content, http://links.lww.com/JRS/A44).

Postoperative

The patient should lie flat for 2 hours to help graft attachment. Intraocular pressure (IOP) should be checked at 1 hour and 2 hours postoperatively. If the IOP is between 21 and 30 mm of Hg, oral acetazolamide tablet (500 mg) and pupil dilation with cyclopentolate 1% and phenylephrine 2.5% should be considered. Higher IOP can be managed by intravenous acetazolamide or release of air from the AC. This can be performed under topical anesthesia at the slitlamp after instilling a drop of 5% povidone-iodine in the conjunctival sac. Air is released by depressing the posterior lip of one of the side ports.

Graft attachment can be evaluated clinically and by anterior segment optical coherence tomography when required. Postoperative medications include a steroid (dexamethasone 0.1%) 6 times a day for 1 week, tapering to 4 times a day for 1 month and slowly thereafter, an antibiotic (chloramphenicol or fluoroquinolone) 4 times a day for 2 to 4 weeks, and a mydriatic (cyclopentolate 1%) twice a day for 3 days. Eyedrops free of preservatives are preferred.

Rebubbling

A clinically attached graft may at times show tiny pockets of detachment (area of nonattachment surrounded all around by attached tissue), which are more obvious on anterior segment optical coherence tomography. These can be observed without immediate need for rebubbling. Segments of separation of the very edge of the graft (curling posteriorly) too can be observed. Larger detachments or areas of nonattachment require rebubbling, which can be performed at the slitlamp or in the operating room.

DISCUSSION

Harvesting PDEK tissue requires the creation of a type 1 big bubble. This depends on achieving a critical intra-tissue pressure of injected air, enough for the air to make its way through the tissue, from the point of entry at the needle tip to the plane between the deep stroma and the PDL, where it accumulates to separate the PDL with the Descemet membrane and endothelial cells from the stroma. Air escaping from the periphery of the scleral–corneal disc reduces the intra-tissue pressure. As more air is injected with greater force to overcome this loss, the syringe empties before a bubble is formed or a bubble forms and bursts under the excessive force of injection. Less commonly, air escapes from peripheral fenestrations in the PDL, central to the attachment of the Descemet membrane, resulting in the formation of a type 2 big bubble, which yields DMEK tissue instead of PDEK tissue.17,20 Both these undesirable outcomes are overcome using the PDEK clamp, which shuts all fenestrations at the periphery. When the clamp is correctly centered on the scleral–corneal disc, air can be injected at any rate into the tissue. As none of it escapes, all air accumulates in the tissue and eventually reaches the critical pressure. The pressure of air egressing at the needle tip relates to the force applied on the plunger (with the thumb) and the diameter of the syringe. For a constant force, a smaller diameter syringe will generate a greater pressure (force per unit area) at the tip of the needle. Accordingly, a 1 mL syringe will generate a greater pressure at the tip than a 5 mL syringe for the same force applied. The total volume of air required to completely fill the clamped corneal tissue is from 0.14 to 0.37 mL with a mean of 0.208 ± 0.08; and the volume of a type 1 big bubble is 0.1 mL.21 The variability is due to the differences in the volume of air that the tissue can accommodate, and the possibility of a type 1 big bubble to form before complete tissue emphysema is attained as air can at times find a more direct path to the pre-Descemet plane.21 PDEK allows the use of younger donor corneas with relatively higher endothelial cell counts, which is not always possible with DMEK tissue. The mean endothelial cell loss at 6 months after PDEK was reported to be 22.13% to 27.4%.14 The mean postoperative central corneal thickness at 6 months was reported as 565.97 ± 44.79 μm and 515 ± 7 μm.14,22 The mean endothelial cell loss with DMEK at 6 months was reported as 24.7% and 41%.23 In an ex vivo study, Altaan et al. have demonstrated that the endothelial cell loss during the preparation of PDEK tissue by pneumodissection is the same, if not less, than for preparation of DMEK tissue by the same method.24

The high elastin content and strength of the PDL and Descemet membrane allow the PDEK tissue to stretch when the big bubble is filled with air and return to the original dimension on deflation.15 This is also seen in the DALK procedure when a type 1 big bubble is formed. Although the PDL has a higher elastin content than the Descemet membrane, the selective distribution of elastin in the anterior part of the Descemet membrane determines the scroll formation of PDEK tissue (and DMEK tissue) with the endothelial cells outside.15 However, the PDL splints the Descemet membrane, and the scroll formed is less tight than that of the Descemet membrane alone.25 This also enables relatively easier unscrolling of the tissue in the eye. The PDL also allows deliberate folding of the tissue (trifold) with the endothelial cells inside the fold. When inserted into the AC, the natural tendency of the tissue to scroll with the endothelial cells outside drives the trifold to unfold spontaneously as the tissue attempts to scroll the other way around. This provides an additional aid in unscrolling of tissue in the AC. Different techniques are used for unscrolling of endothelial keratoplasty tissue, namely the standardized no-touch technique, bubble rolling, 2 parallel cannulas (Dirisamer technique), single sliding cannula, double bubble, and bubble-in-the-roll maneuveurs.26–28 Depending on the type and tightness of the scroll, a combination of these techniques is often required for DMEK and PDEK, but PDEK tissue unscrolls more readily. It is postulated that a greater loss of endothelial cells occurs with longer duration and manipulations associated with unscrolling; hence, it is likely that the loss with PDEK will be comparatively less.24–26 Centration of the unscrolled graft in the eye is achieved by tapping and can be an issue. With PDEK tissue, it is possible to insert a blunt spatula in the AC and stroke the PDL surface of the graft in the desired direction to achieve centration. A similar maneuver with DMEK tissue creates wrinkles and folds in the tissue.

A major advantage of endothelial keratoplasty is the relatively reduced risk for endothelial rejection and related graft failure compared with PK.9 In DMEK, graft rejection has been shown to be 2% at 2 years. This low incidence of rejection is attributed to the absence of stromal tissue (and associated keratocytes) from DMEK transplant with subsequent decrease of antigenic load.9 The need for steroid drops postoperatively is less, which is of particular relevance in steroid responders. In PDEK grafts too there is no stroma and the PDL has very few if any keratocytes.12,29 No PDEK graft rejection has yet been reported, but the operation is relatively new, and long-term outcomes are awaited.

The PDEK technique is not without its limitations. The size of a PDEK graft is restricted by the diameter of a type 1 big bubble, which is 8.0 to 8.5 mm, and the resultant graft tissue diameter is less than that.12,20 This would reduce the total number of endothelial cells transplanted compared with DMEK in which the standard size is between 8.0 and 9.0 mm. However, this can be partially offset in younger donors, with their higher counts, for PDEK compared with DMEK in which harvesting tissue is not possible or difficult. Moreover, experience with hemi-DMEK and quarter DMEK shows similar visual outcomes to DMEK despite the decreased number of endothelial cells transplanted. Comparative ease of handling and unscrolling of PDEK tissue could offer an advantage in limiting endothelial cell loss intraoperatively.25,30–34

At the present state of available evidence, however, this has to be a theoretical consideration. Another limitation of PDEK is the manual excision of the graft after creation of the type 1 big bubble. New means of cutting or trephination of PDEK tissue are being developed but have to be tested and validated. Nevertheless, the preparation technique for PDEK tissue is simple, does not require expensive equipment (like for DSAEK or ultra-thin DSAEK), and is amenable to preprepared tissue being supplied by eye banks.

Few reports exist in the literature on the results of the PDEK technique. The first report on PDEK showed the results in 5 eyes with a postoperative mean best-corrected visual acuity of 0.6.13 Agarwal et al. showed the results in 3 eyes with young donor corneas (9 to 12 months old).14 Huang et al. reported results in 20 patients with a success rate of 90%.33 Ponniah and Agarwal presented the results of PDEK in 48 eyes.22 Klimesova et al. showed the results of combined phacoemulsification and PDEK.35 The results of these studies are summarized in Table 1.

Table 1.
Table 1.:
Summary of studies on pre-Descemet endothelial keratoplasty.

PDEK is an evolving technique, which offers considerable advantages in relation to both preparation and handling techniques and surgery. This should help and facilitate surgeons to convert from DSEK/DSAEK to PDEK, especially when the challenges of DMEK are considered to be a limiting factor. A standardized approach to surgery, as laid out in this article, will help in improving outcomes.

WHAT WAS KNOWN

  • Pre-Descemet endothelial keratoplasty (PDEK) is an alternative technique to Descemet membrane endothelial keratoplasty (DMEK) with possible advantages.
  • PDEK tissue preparation requires type 1 bubble formation.
  • PDEK tissue is easy to handle compared with DMEK.

WHAT THIS PAPER ADDS

  • A standardized technique for harvesting and transplanting PDEK tissue.
  • Tips on maximizing success with the PDEK clamp.
  • A review of the outcomes of PDEK published thus far.

REFERENCES

1. Zhang YY, Xie LX. Clinical research progress in endothelial keratoplasty [in Chinese]. Zhonghua Yan Ke Za Zhi 2017;53:714–720
2. Pavlovic I, Shajari M, Herrmann E, Schmack I, Lencova A, Kohnen T. Meta-Analysis of postoperative outcome parameters comparing descemet membrane endothelial keratoplasty versus descemet stripping automated endothelial keratoplasty. Cornea 2017;36:1445–1451
3. Parekh M, Ruzza A, Romano V, Favaro E, Baruzzo M, Salvalaio G, Grassetto A, Ferrari S, Ponzin D. Descemet membrane endothelial keratoplasty learning curve for graft preparation in an eye bank using 645 donor corneas. Cornea 2018;37:767–771
4. Debellemanière G, Guilbert E, Courtin R, Panthier C, Sabatier P, Gatinel D, Saad A. Impact of surgical learning curve in descemet membrane endothelial keratoplasty on visual acuity gain. Cornea 2017;36:1–6
5. Phillips PM, Phillips LJ, Muthappan V, Maloney CM, Carver CN. Experienced DSAEK surgeon's transition to DMEK: outcomes comparing the last 100 DSAEK surgeries with the first 100 DMEK surgeries exclusively using previously published techniques. Cornea 2017;36:275–279
6. Li S, Liu L, Wang W, Huang T, Zhong X, Yuan J, Liang L. Efficacy and safety of Descemet's membrane endothelial keratoplasty versus Descemet's stripping endothelial keratoplasty: a systematic review and meta-analysis. PLoS One 2017;12:e0182275
7. Parekh M, Leon P, Ruzza A, Borroni D, Ferrari S, Ponzin D, Romano V. Graft detachment and rebubbling rate in Descemet membrane endothelial keratoplasty. Surv Ophthalmol 2018;63:245–250
8. Rose-Nussbaumer J, Alloju S, Chamberlain W. Clinical outcomes of descemet membrane endothelial keratoplasty during the surgeon learning curve versus descemet stripping endothelial keratoplasty performed at the same time. J Clin Exp Ophthalmol 2016;7:599
9. Anshu A, Price MO, Price FW Jr. Risk of corneal transplant rejection significantly reduced with Descemet's membrane endothelial keratoplasty. Ophthalmology 2012;119:536–540
10. Madi S, Leon P, Nahum Y, DʼAngelo S, Giannaccare G, Beltz J, Busin M. Five-year outcomes of ultrathin descemet stripping automated endothelial keratoplasty. Cornea 2019;38:1192–1197
11. Dua HS, Faraj LA, Branch MJ, Yeung AM, Elalfy MS, Said DG, Gray T, Lowe J. The collagen matrix of the human trabecular meshwork is an extension of the novel pre-Descemet's layer (Dua's layer). Br J Ophthalmol 2014;98:691–697
12. Dua HS, Faraj LA, Said DG, Gray T, Lowe J. Human corneal anatomy redefined: a novel pre-Descemet's layer (Dua's layer). Ophthalmology 2013;120:1778–1785
13. Agarwal A, Dua HS, Narang P, Kumar DA, Agarwal A, Jacob S, Agarwal A, Gupta A. Pre-Descemet's endothelial keratoplasty (PDEK). Br J Ophthalmol 2014;98:1181–1185
14. Agarwal A, Agarwal A, Narang P, Kumar DA, Jacob S. Pre-Descemet endothelial keratoplasty with infant donor corneas: a prospective analysis. Cornea 2015;34:859–865
15. Mohammed I, Ross AR, Britton JO, Said DG, Dua HS. Elastin content and distribution in endothelial keratoplasty tissue determines direction of scrolling. Am J Ophthalmol 2018;194:16–25
16. White TL, Lewis PN, Young RD, Kitazawa K, Inatomi T, Kinoshita S, Meek KM. Elastic microfibril distribution in the cornea: differences between normal and keratoconic stroma. Exp Eye Res 2017;159:40–48
17. Dua HS, Said DG. Pre-Descemets endothelial keratoplasty: the PDEK clamp for successful PDEK. Eye (Lond) 2017;31:1106–1110
18. Barraquer R, Alvarez de Toledo J. Queratoplastias: nuevas tecnicas para el siglo XXI. Madrid, Spain: Sociedad Española de Oftalmología; 2016
19. Jacob S, Agarwal A, Agarwal A, Narasimhan S, Kumar DA, Sivagnanam S. Endoilluminator-assisted transcorneal illumination for Descemet membrane endothelial keratoplasty: enhanced intraoperative visualization of the graft in corneal decompensation secondary to pseudophakic bullous keratopathy. J Cataract Refract Surg 2014;40:1332–1336
20. Dua HS, Faraj LA, Kenawy MB, AlTaan S, Elalfy MS, Katamish T, Said DG. Dynamics of big bubble formation in deep anterior lamellar keratoplasty by the big bubble technique: in vitro studies. Acta Ophthalmol 2018;96:69–76
21. AlTaan SL, Mohammed I, Said DG, Dua HS. Air pressure changes in the creation and bursting of the type-1 big bubble in deep anterior lamellar keratoplasty: an ex vivo study. Eye (Lond) 2018;32:146–151
22. Ponniah L, Agarwal A. Why I prefer PDEK (Pre Descemets Endothelial Keratoplasty). Advantages over DSEK/DMEK/PK. Eucornea; October 6, 2017; Lisbon
23. Stuart AJ, Romano V, Virgili G, Shortt AJ. Descemet's membrane endothelial keratoplasty (DMEK) versus Descemet's stripping automated endothelial keratoplasty (DSAEK) for corneal endothelial failure. Cochrane Database Syst Rev 2018;6:Cd012097
24. Altaan SL, Gupta A, Sidney LE, Elalfy MS, Agarwal A, Dua HS. Endothelial cell loss following tissue harvesting by pneumodissection for endothelial keratoplasty: an ex vivo study. Br J Ophthalmol 2015;99:710–713
25. Dua HS, Termote K, Kenawy MB, Said DG, Jayaswal R, Nubile M, Mastropasqua L, Holland S. Scrolling characteristics of pre-descemet endothelial keratoplasty tissue: an ex vivo study. Am J Ophthalmol 2016;166:84–90
26. Liarakos VS, Dapena I, Ham L, van Dijk K, Melles GR. Intraocular graft unfolding techniques in descemet membrane endothelial keratoplasty. JAMA Ophthalmol 2013;131:29–35
27. Hayashi T, Kobayashi A. Double-bubble technique in descemet membrane endothelial keratoplasty for vitrectomized eyes: a case series. Cornea 2018;37:1185–1188
28. Akbaba Y, Weller JM, Rossler K, Armitage WJ, Schlotzer-Schrehardt U, Kruse FE, Tourtas T. “Bubble-in-the-Roll” technique using the endoject DMEK injector: influence of the air bubble on endothelial cell loss. Cornea 2017;36:1576–1579
29. Schlotzer-Schrehardt U, Bachmann BO, Tourtas T, Torricelli AA, Singh A, Gonzalez S, Mei H, Deng SX, Wilson SE, Kruse FE. Ultrastructure of the posterior corneal stroma. Ophthalmology 2015;122:693–699
30. Birbal RS, Hsien S, Zygoura V, Parker JS, Ham L, van Dijk K, Dapena I, Baydoun L, Melles GRJ. Outcomes of hemi-descemet membrane endothelial keratoplasty for fuchs endothelial corneal dystrophy. Cornea 2018;37:854–858
31. Zygoura V, Baydoun L, Ham L, Bourgonje VJA, van Dijk K, Lie JT, Dapena I, Oellerich S, Melles GRJ. Quarter-Descemet membrane endothelial keratoplasty (Quarter-DMEK) for Fuchs endothelial corneal dystrophy: 6 months clinical outcome. Br J Ophthalmol 2018;102:1425–1430
32. Saint-Jean A, Soper M, Den Beste K, Iverson S, Price MO, Price FW. Technique for ensuring type I bubble formation for pre-descemet endothelial keratoplasty preparation. Cornea 2019;38:1336–1338
33. Huang T, Jiang L, Zhan J, Ouyang C. Pre-descement membrane endothelial keratoplasty for treatment of patients with corneal endothelial decompensation [in Chinese]. Zhonghua Yan Ke Za Zhi 2018;54:105–110
34. Agarwal A, Narang P, Kumar D, Agarwal A. Young donor–graft assisted endothelial keratoplasty (PDEK/DMEK) with epithelial debridement for chronic pseudophakic bullous keratopathy. Can J Ophthalmol 2017;52:519–526
35. Klimesova Y, Hlozankova K, Krizova D, Klezlova A, Studeny P. Clinical outcomes of triple procedure pre-Descemet's endothelial keratoplasty (PDEK) and cataract surgery. ESCRS; October 7–11, 2017; Lisbon

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