Corneal transplantation (penetrating keratoplasty (PK)) was first performed by Zirm over 104 years ago. Until recently there have been few changes compared to the original surgery, however over the last decade there have been dramatic improvements in surgical techniques (1). There are many complications related to conventional penetrating keratoplasty e.g. poor ocular surface healing, neutrophic cornea, suture related complications, graft rejection, tectonically weak eyes and high graft astigmatism hence surgeons have been looking at more selective tissue lamellar transplantation techniques to circumvent some of these problems.
The cornea is comprised of essentially 3 main layers, the epithelium, the stroma and the descemet's membrane (DM)/endothelial cell complex. Selective tissue transplantation procedures have taken the form of either anterior lamellar keratoplasty (ALK) in which the epithelium and stroma are replaced or endothelial keratoplasty (EK) in which essentially the DM/endothelial cell complex is replaced, with or without a posterior stromal carrier for support. In patients with purely corneal endothelial dysfunction, selective tissue transplantation, in the form of endothelial keratoplasty, has emerged as a viable alternative to full thickness conventional penetrating keratoplasty. The 2010 EBAA (Eye Banks Association of America) Statistical Report revealed that of the 42, 642 corneal transplants performed in the US, 19,159 were EK procedures, representing 44.9% of all transplants, a 9.5% increase compared to 2009. In Europe, EK is also becoming a mainstream procedure (constituting 28% of all grafts in the UK), whereas Asia has been slower to adopt EK with Singapore being an exception—in 2010, 36% of all transplants in Singapore were EK procedures. Endothelial dysfunction is the leading cause of corneal transplantation in Singapore and USA, as well as in many European countries such as the UK and Sweden.
Endothelial keratoplasty was first described by Melles in 1998. The surgery involves manual dissection of both the donor and the recipient cornea and transplantation of essentially the donor posterior stroma with DM and endothelium (Deep lamellar endothelial keraoplasty (DLEK)). The surgery requires special instrumentation but obviated the need for surface sutures as in PK. Hence a proof of concept was established. Due to the interface between the donor and recipient stroma, haze was often noted at the interface and this led to a reduction in best spectacle-corrected visual acuity. However the results were equivalent to those achieved with PK surgery with respect to visual acuity outcomes but the surgery often took many hours. To combat the problem of the interface and the manipulation in the recipient cornea, Melles described a technique where the recipient endothelium was simply stripped off in a technique called descemet's stripping endothelial keratoplasty (DSEK). This removed the need for dissection of the recipient cornea and reduced surgical time dramatically. However, the donor cornea was still transplanted as a 150-250 micron thick donor lenticule comprising of posterior stroma DM/endothelium. Since there was minimal dissection of the recipient cornea, the donor lenticule effectively protruded from the posterior edge of the cornea into the anterior chamber. Price et al further improved the surgery by involving the use of an automated machine to cut the donor lenticule. This provided a smoother stromal interface of the donor lenticule and allowed for a more consistent thickness of the donor lenticule, compared to the original manual dissection technique (DSEK). This surgery was coined DSAEK (Descemet stripping automated endothelial keratoplasty).
DSAEK has become synonymous with endothelial transplantation and is currently the dominant form of EK worldwide, accounting for well over 90% of all EK procedures, and results have been shown to be equivalent and in some centres superior to penetrating keratoplasty, and recently has been shown to have a significantly lower rate of transplant rejection as compared to PK. Essentially it is sutureless, small incision corneal transplantation surgery. There are no sutures on the ocular surface and the posterior cornea is accessed by a 5 mm scleral incision. The recipient DM/diseased endothelium is stripped off and the donor cornea is inserted into the anterior chamber of the recipient. The new graft is then positioned against the recipient posterior stroma using air tamponade for 8 min. Following which there is air fluid exchange, leaving the anterior chamber with an 75% air fill overnight.
Even though visual acuity results and outcomes have been highly encouraging with this surgery, the operation is not an exact anatomical tissue replacement procedure. The donor cornea is made up of stroma DM/endothelium hence it is not an exact tissue replacement since the recipient is prepared by stripping the diseased DM/endothelium. This may compromise the donor due to the extra thickness in eyes with shallow anterior chamber or with anterior chamber intraocular lenses, and anterior chamber comprise with peripheral anterior synechiae is a well known complication. Also it adds a potential second interface between the donor stroma and the recipient which may further degrade visual quality.
sDMEK (Descemets Membrane Endothelial Keratoplasty
Melles in 2006, subsequently described a technique called descemet membrane endothelial keratoplasty (DMEK). In this technique just the DM/endothelium was harvested from a donor and then transplanted into a recipient in which DM/endothelium was stripped. DMEK potentially offers major advantages over the earlier three techniques. Firstly, visual rehabilitation is much faster. Secondly, a near perfect anatomical restoration of the recipient cornea in DMEK has clearly been proven to provide better optical quality of the recipient cornea, with a significantly higher percentage of patients attaining perfect (6/6) best correction visual acuity, and thirdly, in contrast to DSAEK in which the donor is prepared by automated therapeutic lamellar keratoplasty unit to produce a 100-250 microns thick tissue, the donor DM/endothelium can be peeled off directly in DMEK, and hence does not require the need for additional expensive surgical equipment. Also the transplantation of only the DM/endothelium has led to reportedly reduced rates of graft rejection, even surpassing that of DSAEK. A recent article currently in press by Price et al showed that rejection rates in PK, DSAEK and DMEK in Fuchs' and pseudophakic bullous keratoplasty were 17%, 9% and 0.7% respectively.
The major challenge of DMEK is three-fold:
(1) the harvesting of the DM/endothelial complex without excessive endothelial cell damage;
(2) the difficulty in handling the 10 micron DM sheet, which tends to ‘roll up’ due to its thickness (only 10 microns). Since the roll develops with the endothelial cells on the outside there is further damage to the endothelium when the “Descemet-roll” is unrolled in the eye before tamponading to the recipient cornea.
(3) unscrolling the DM roll in the anterior chamber to allow attachment to the recipient.
Currently only a small handful of surgeons worldwide are performing DMEK on a routine basis, simply because of the surgical challenges described above. While donor preparation techniques have generally been solved, with several techniques described now enabling effective donor stripping with minimized tissue loss from tearing or endothelial damage, the major challenge in DMEK lies in handling the scrolled DM which always scrolls with the endothelial surface outwards, so that any handling results in endothelial cell damage. Tight scrolling is often encountered in young donors below the age of 40 years, and hence only older donors over the age of 50 years are generally used in DMEK surgery (another reason to use older donors is that DM stripping of the donor is also more difficult in younger donors). Insertion of this scroll of DM is relatively simple to achieve through a small corneal or scleral incision, usually be placing the scroll into a IOL or Phakic IOL cartridge injector and injecting the scroll into the AC, but he main surgical challenge lies in unscrolling the donor into the right endothelium-down orientation in the AC, and aligning the donor centrally, and without wrinkling onto the posterior surface of the recipient cornea.
This is achieved by injecting short bursts of BSS with a cannula through several paracentesis ports to initiate unscrolling, injecting various sizes of air bubbles beneath the donor to further unscroll the tissue, and finally injecting the AC with a full chamber of air to achieve tamponade and adherence of the donor to the recipient cornea. This process may take anywhere from 10 minutes to an hour to perform, and as a results, currently, only 3 main surgeons (Melles in Rotterdam, Price in the US, and Kruse in Germany) have reported in reasonable series of DMEK cases. Despite this, their studies collectively report much better visual results compared to DSEK, but with a higher rate of donor rebubbling due to residual donor detachment, and endothelial cell loss rates which are higher, or just able to match DSEK cell loss rates. Many corneal surgeons today feel that DMEK will never become a mainstream procedure unless the surgery becomes technically easier and more predictable.
It is the broad objects of the present invention to provide a novel method and system for aiding manipulation of the thin DM/endothelial complex, so as to greatly simplify the donor handling, and AC manipulation stages, of DMEK surgery.
It has now been found that certain of the foregoing and related objects of the invention are attained by the provision of a method for performing DMEK surgery, wherein the improvement comprises:
providing a thin, flexible, self-supporting, generally circular carrier mat having elastic memory and an hydrophilic surface;
inserting the carrier mat under a descemet's membrane separated from a donor stroma with the endothelial surface on the membrane upwardly disposed and out of contact with the carrier mat, and with the hydrophilic surface of the carrier mat in contact with the surface of the membrane opposite to the endothelial surface;
centering the descemet's membrane on the carrier mat with an annular marginal portion of the carrier mat surrounding the membrane and extending therebeyond, and causing the membrane to lie in a flat, wrinkle-free condition on the carrier mat;
providing a glide capsule that is constructed to form the assembled carrier mat and carried membrane into a double-coiled scrolled configuration upon being drawn thereinto, and for introducing the membrane assembly, in double-coiled scrolled configuration, into the anterior chamber of a recipient's eye;
drawing the carrier mat and membrane assembly into the glide capsule to form the assembly into a double-coiled scrolled configuration with the endothelial surface of the membrane facing inwardly and with no area of epithelial cells in substantial contact with any other such area thereof;
using the glide capsule to transfer the membrane, in double-coiled scrolled configuration and proper orientation, into the anterior chamber of a recipient's eye through an incision on one side of the anterior chamber by initially partially inserting the glide capsule into the incision on the one side of the anterior chamber;
grasping a marginal portion of carrier mat, using an instrument inserted through an incision on the opposite side of anterior chamber, and withdrawing the carrier mat partially from glide capsule;
drawing the descemet's membrane away from the carrier mat, by force applied to the membrane using an instrument inserted through the opposite-side incision, and into the anterior chamber;
withdrawing the glide capsule from the incision on the one side of the anterior chamber while maintaining restraining force on the descemet's membrane, as necessary, and together with the glide capsule withdrawing the carrier mat, partially retained in the glide capsule, from the anterior chamber, leaving the membrane within the anterior chamber;
causing the descemet's membrane to unscroll within the anterior chamber, the proper orientation being such that the endothelial surface is downwardly oriented and the carrier mat being fabricated from a polymer that is sufficiently flexible and soft, and that has sufficient tensile strength and resistance to tearing, to permit it to perform the carrier functions, and to withstand the manipulations required, in carrying out the method.
Normally, the carrier mat will be about 30 to 100 millimeters thick; the surrounding annular portion, extending beyond the descemet's membrane, will be about 0.5 millimeter in radial width, with the diameter of the descemet's membrane being about 8 to 9 millimeters; the carrier mat will have an inherently arcuate cross section, with the hydrophilic surface thereof inwardly disposed; and the polymer from which the carrier mat is fabricated will be a silicone hydrogel.
Other objects of the invention are attained by the provision of a system for performing DMEK surgery comprising, in combination: a thin, flexible, self-supporting circular carrier mat having an elastic memory and an hydrophilic surface; and an inserter comprised of glide capsule having open opposite ends and an interior chamber, and being constructed to receive the carrier mat through one of the open ends and to form said mat into a double-coiled scrolled configuration upon being drawn into the interior chamber thereof. The carrier mat will normally have the features hereinabove and hereinafter disclosed. The guide capsule will preferably be constructed forwardly tapered conical portion, terminating in an open end, and will be constructed to provide a ridge that extends between the open ends for assisting in forming the carrier mat into such a double-coiled scrolled configuration.
The supporting and transfer, or carrier disc or mat, employed in the practice of the present invention, sometimes referred to by the trade designation “DMat,” is a device that affords structural rigidity to the thin DM/endothelial complex to:
a) prevent inadvertent scrolling;
b) prevent wrinkling;
c) prevent inadvertent eversion of the donor;
d) allow for handling of the donor using the carrier mat, thus reducing endothelial damage; and
e) facilitate donor entry and manipulation in the AC.
The Carrier Mat, generally designated by the numeral 10 in
While, as noted above, a preferred material for fabrication of the Carrier Mat is a silicon hydrogel, other suitable polymers will be apparent to those skilled in the art in view of the disclosure of the present specification. Additional information concerning suitable materials is provided in International Publication WO 2012/118681, the pertinent disclosure of which publication is incorporated hereinto by reference thereto.
The DMEK Inserter, depicted in
With regard to the internal diameter of the Glide Capsule 18, for a 9 millimeter DMEK donor on a 10 millimeter Carrier Mat, one may double coil this DM complex through a minimum diameter of 2.9 millimeters without a central ridge. With a central ridge 24 of 0.5 millimeter in length, it is further possible to utilize a 2.57 millimeter internal diameter without endothelial touch or overlap. As such, the minimum internal diameter of the Glide Capsule will be in the region of 2.60 to 3.00 millimeters. Accounting for the thickness of the walls, the Glide Capsule 18 will be tapered such that the leading or front portion will be approximately 2.7 to 3.0 mm, while the back portion will measure around 3.5 to 4.00 millimeters. The internal ridge 24 will prevent endothelial touch, as in the prior version, and the Capsule will be sealed by the Glide Introducer 20 to ensure a complete seal.
The well of the Preparation Base (not shown in the append drawings) will be more elevated compared to the original EndoGlide device so as to receive the Carrier Mat/DM complex without placement of an anterior lamellar cap.
Product 3: Detachable curved DMEK Intraocular Forceps and Accompanying Sponge Support
The Detachable curved DMEK Intraocular Forceps, shown in
DMEK Surgical Technique using the Carrier Mat and the DMEK Inserter Device
The curved Carrier Mat is then carefully slid under the DM while it is still lying flat in the donor block chamber, again ensuring that excessive fluid is not present to initiate scrolling, and that the endothelial surface is not touched during the sliding process. The Carrier Mat is sized to be 1 millimeter larger than the dissected DM, and thus would be available in a variety of diameters, or conversely can be trephined to the right size by the surgeon. Following placement of the DM on the Carrier Mat, careful centering of the DM on the Carrier Mat is performed to ensure that an equal 0.5 millimeter exposure of the Carrier Mat is achieved all around the DM, and that the DM lies completely flat and unwrinkled on the Carrier Mat. Gentle wicking away of excess fluid around the edge of the Carrier Mat and in the suction block chamber is the performed to enable the DM to fully contact the Carrier Mat with minimal intervening fluid, so that the DM now is moderately adherent to the Carrier Mat by capillary action.
The Carrier Mat/DM complex is slid under a Paton spatula and placed onto the well of the Glide Capsule, with the Carrier Mat tab (if any) adjacent to the Glide Capsule opening.
The device is inserted into the AC through the 4.6-3.5 millimeter incision. Once fully inserted into the AC, and with an AC maintainer present on low flow so as to achieve a slightly shallow, but intact anterior chamber, DMEK intraocular forceps is introduced through a nasal paracentesis, and is used to grasp the tab of the Carrier Mat. The Carrier Mat is then gradually pulled halfway out of the Glide Capsule, into the AC, and is released. The same forceps then is used to grasp the leading edge of the DM complex and the DM complex is gently pulled away from the Carrier Mat, out of the Glide Capsule, and fully into the AC. While still holding onto the DM complex, the Glide Capsule is then carefully retracted out of the eye, and the Carrier Mat will also follow with the Glide Capsule, detaching itself completely from the DM complex. Once the Glide Capsule and Carrier Mat is fully out of the eye, a small air bubble is injected with a 30 G needle under the uncoiling DM complex.
The DM complex is fully uncoiled and opened with the use of BSS and air bubble injection, while it is still held by the intraocular forceps. The handle of the intraocular forceps may be detached from the head and cannula of the forceps while still holding onto the DM complex, and the head and cannula is supported by the foam support which is placed under the head of the cannula, over the nasal canthal area. This enables the surgeon to let go of the forceps which is still holding the DM complex in place so that both hands are free to inject BSS and air and maneuver the DM complex into a fully uncoiled and central position just under the recipient cornea. Once the DM complex is perfectly positioned in relation to the recipient cornea, more air is injected to ensure stability of the DM com-plex, and finally the forceps hold on the DM complex can be released using the clip on the head of the forceps. The corneal or scleral wound is sutured, the AC maintainer removed and the wound sutured, and a complete air fill with air tamponade completes the DMEK procedure.
This application claims the benefit of U.S. Provisional patent Application No. 61/541,431, filed Sep. 30, 2011, the entire specification of which is incorporated hereinto by reference.
Number | Date | Country | |
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61541431 | Sep 2011 | US |