Descemet's stripping endothelial keratoplasty
Descemet stripping endothelial keratoplasty (DSEK) is a type of endothelial keratoplasty (EK) procedure where the host endothelium and Descemet’s membrane (DM) are replaced by the donor endothelium and DM, along with a small amount of posterior stromal thickness, through a corneal or corneoscleral incision.
EK is a partial-thickness corneal transplant technique that involves selective replacement of the diseased endothelium along with the DM, providing faster visual rehabilitation and fewer intraoperative and postoperative complications when compared with full-thickness penetrating keratoplasty (PK), a procedure in which all corneal layers are replaced.
The first successful case of EK was reported by Charles Tillet in 1956, who sutured the posterior corneal button to the host bed, however, the technique was not widespread. It was not until the late 1990s that a major breakthrough occurred, when Melles et al. described a sutureless technique that the author named posterior lamellar keratoplasty (PLK), where an air bubble was used to held in place the donor tissue to the host cornea. Mark Terry adopted and modified this technique in 2001, renaming it deep lamellar endothelial keratoplasty (DLEK). The DLEK technique was not universally accepted due to its high surgical skill demands, which led Melles et al. to simplify it by selectively removing the DM and endothelium from the host cornea, eliminating the need to dissect the host corneal stroma. In 2005, Francis Prince published the results of this technique, naming it DSEK. One year later, Gorovoy reported the use of an automated microkeratome in the dissection of the donor cornea to improve the graft-host interface, in a procedure named Descemet stripping automated endothelial keratoplasty (DSAEK). The use of the microkeratome allowed eye banks to process and pre-cut corneal tissue, leading to the popularization of DSAEK, which quickly surpassed PK as the procedure of choice in patients with endothelial dysfunction.
Currently, DSAEK remains the most commonly performed EK procedure worldwide. Nevertheless, newer techniques keep being developed to improve EK. In 2006, Melles et al. described another technique in which only the donor endothelium and DM were transplanted and not the posterior stroma and named it Descemet’s membrane endothelial keratoplasty (DMEK). This technique was later modified by retaining a rim of posterior corneal stroma along the periphery of the donor tissue, which was called Descemet’s membrane automated endothelial kerotoplasty (DMAEK), a hybrid of DSAEK and DMEK.
According to the Eye Bank Association of America, the number of PK procedures performed in the United States of America (USA) has decreased 54.4% from 2005 to 2015, while EK has been the most commonly performed keratoplasty procedure in the last few years and continues to increase. 27,208 EK procedures have been performed in 2015, which corresponds to a 4.8% increase, following a 3.9% increase in 2014 and 8.4% increase in 2013. DSEK/DSAEK is the most commonly performed EK technique, with 22,514 procedures done in 2015, a number that has been relatively similar since 2011. While the number of DMEK/DMAEK procedures remains lower by comparison (4.694 procedures in 2015), it has been constantly increasing in the last few years: 63.5% in 2015, following an increase of 88.2% in 2014 and a 103.5% increase in 2013.
The most common indication for EK in 2015 was by far Fuchs’ dystrophy (47.1%), followed by pseudophakic bullous keratopathy (17.5%).
EK has become the procedure of choice in the surgical treatment of patients with any type of endothelial dysfunction such as endothelial dystrophies (Fuchs’ endothelial dystrophy, congenital hereditary endothelial dystrophy, posterior polymorphous dystrophy), pseudophakic and aphakic bullous keratopathy, endothelial decompensation caused by prior intraocular surgery, trauma or glaucoma drainage devices, iridocorneal endothelial (ICE) syndrome and endothelial failure postpenetrating keratoplasty.
The ideal candidate for DSEK/DSAEK is a pseudophakic patient with an in-the-bag intraocular lens (IOL), an intact posterior capsule, a deep anterior chamber, corneal pathology limited to the endothelium, absence of corneal scars or significantly reduced corneal thickness and a relatively normal iris and anterior chamber angle. Those who are not pseudophakic should have cataract surgery before or in combination with the EK procedure.
DSEK/DSAEK is a more versatile procedure than DMEK, with a large number of reports supporting its role in complex EK scenarios where DMEK is not advisable, such as aniridia or large iris defects, presence of an anterior chamber IOL, postglaucoma surgery, previous failed PK or EK procedure and ICE syndrome10–12  .
EK is not indicated in patients with visual limiting stromal scarring or opacity as well as in diseases that do not affect the corneal endothelium such as corneal ectasia (keratoconus, keratoglobus, pellucid marginal degeneration and others), anterior dystrophies or in hypotonic eyes.
Advantages over PK
- Faster visual recovery
- Minimal topographic changes (marked reduction of astigmatism)
- Smaller incision
- Small and predictable hyperopic shift
- Tectonically resistant globe
- No suture-related complications
- Lower incidence of allograft rejection
Donor cornea evaluation
According to the Eye Bank Association of America, tissue may be used for transplantation from donors aged from 2 to 75 years. In the USA, the general consensus among corneal surgeons and eye banks was not to use donor tissue preserved for more than 7-8 days, with 96% of donor corneas preserved for a maximum of 7 days in the Cornea Preservation Time Study (CPTS). The CPTS is a prospective multicenter randomized trial designed to potentially increase the donor tissue supply by expanding options for its use and strengthening the evidence base for increasing preservation time up to the Food and Drug Administration-approved 14 days.
Optimal donor tissue should have approximately 16-18 mm of scleral rim, uniform thickness (classically of approximately 180 µm but nowadays surgeons tend to prefer thinner grafts) with a smooth stromal surface, 7-9 mm of donor disk diameter and an endothelial cell density of at least 2400 cells/mm with a minimum 60% of hexagonality.
- Preparation of the donor tissue may be performed by the surgeon immediately before surgery or by an eye bank prior to tissue shipment. In DSAEK tissue preparation, the appropriate microkeratome blade depth is chosen based on pachymetry measurement. The tissue is then placed in an artificial anterior chamber and a microkeratome is used to slice the anterior cornea, keeping the endothelium, DM and a thin layer of posterior stroma.
- 1 to 3 paracentesis incisions are made with a 15-degree blade or a 1 mm diamond blade.
- Filling of the anterior chamber with a cohesive viscoelastic.
- Creation of a superior, temporal or along the axis of astigmatism 3-5 mm anterior chamber incision (scleral, limbal or clear cornea in location).
- 360-degree scoring and stripping of the endothelium and DM with a reverse Sinskey or Price hook (descemetorhexis).
- Donor tissue insertion either with noncompression forceps, tissue glides, or various other tissue inserters. Care should be taken in the manipulation of the tissue as it may result in endothelial cell loss.
- Incision closure with 10-0 nylon sutures.
- Injection of balanced salt solution or air to completely unfold the tissue, making sure it is centered.
- Injection of an air bubble underneath the tissue to create apposition between the donor and host corneal stroma.
- Placement of a peripheral iridectomy to minimize the risk of pupillary block.
- Subconjuntival antibiotic and corticoisteroid injections may be administered.
After the procedure, patients are advised to lie supine for at least 24 hours to ensure that the air bubble continues to oppose the donor and host stroma. The air bubble can be released to a 60-70% anterior chamber fill an hour after the surgery at the slit lamp if the surgeon chooses to leave the air fill to maximize apposition. Typically, a protective shield is placed and the patient starts topical antibiotics (usually a second or third generation fluoroquinolone) and steroids 4 times a day and cycloplegics 3 times a day on the day of surgery or the next day. Steroids are tapered at approximately 4 to 6 weeks (the patient may be maintained on 1 drop a day for a long period of time), while antibiotics are used for 10 days and cycloplegics are used as long as the air bubble is present (usually for 1 or 2 days).
The patient is usually seen in the next day, then in 1 week, 1 month and 3 months. Some clinicians prefer to follow the patient closely in the first week to document the remaining air bubble and if there is detachment of the graft.
Most of these complications occur less frequently with increased surgical experience and are also related with the technique used.
Graft preparation complications
- DSEK – perforation of the tissue, creation of a lenticule with irregular surface.
- DSAEK – perforation of the tissue (much less probable than with DSEK), damage to the endothelium, decentered cut.
- Graft tissue flipping or expulsion
- Endothelial trauma
- Inability to maintain a full air fill
- Cataract development (if phakic), anterior or posterior IOL dislocation (if pseudophakic)
- Graft dislocation: usually occurs in the first few days, with rates of 1.5-28%.The graft may need to be repositioned with a repeated air injection if completely detached.
- Primary graft failure: almost entirely due to direct result of iatrogenic trauma (although other causes are described), with rates of 0-29% with an average of 5% in a 2009 review of safety and outcomes of DSEK. Treatment requires reoperation with new donor tissue (EK or PK, depending on the patient and cause of failure).
- Secondary graft failure: in a large prospective series by Terry et al, endothelial cell loss ranged from 25-54% at 6 months and 24-61% at 12 months, with an average of 34% at 6 months that remained relatively stable up to 12 months. Price et al reported 5-year graft survival rates for DSEK of 95% for Fuchs’ dystrophy and 76% for pseudophakic or aphakic corneal edema, results that were similar to those reported for PK in the Cornea Donor. Studies have also shown that rates of endothelial cell loss are higher in eyes with previous glaucoma surgery (15.9% in the group with previous glaucoma surgery vs 3.2% in the group without previous surgery).
- Graft rejection: less frequent with DSEK than with PK, with rates as low as 4% at 3 years. Treatment requires frequent instillation of topical steroids but it may be necessary to use oral or subconjuntival steroids. If medical therapy fails, a new EK procedure should be performed.
- Air bubble-related pupillary block. Endothelial toxicityand IOL opacification have also been described as possible air bubble-related complications.
- Secondary glaucoma: rates of 0-54%, steroid-induced being the most common cause.
- Potential interface haze or epithelial ingrowth.
- Cystoid macular edema: rates of 1.6-5%.
- Infectious complications such as endophthalmitis and interface keratitis are rare.
- Suprachoroidal hemorrhage (rare).
Visual rehabilitation after DSEK/DSAEK is faster than with PK, with many patients recovering in a matter of weeks.
- Mean best spectacle-corrected visual acuity (BSCVA) at 6 months: 20/38 - 20/26, with 79-97% BSCVA ≥ 20/40 and 2-26% BSCVA ≥ 20/20.
- Mean BSCVA improves from 20/30 at 6 months to 20/25 at 3 years, with an increase of 11.1% to 47.2% of patients achieving BSCVA of 20/20 in this period of time.
- Unlike PK, which often yields high irregular astigmatism, DSEK/DSAEK, with a 3-5 limbal, scleral or clear cornea incision, induces low levels of topographic changes and refractive astigmatism. A study by Bahar et al reported that mean astigmatism in DSAEK was 1.36±0.92 diopters while in PK it was 3.78±1.01 diopters, with similar results in other studies.
- Mean final spherical equivalent is close to neutral, as the anterior corneal surface remains relatively unchanged. On the contrary, the changes in the posterior corneal surface induce a hyperopic shift of about 0.8-1.25 diopters.
Ultrathin DSAEK (UT-DSAEK) is a recently introduced procedure that uses graft tissue with thicknesses less than 100µm to improve DSAEK’s visual outcomes. Two microkeratome passes create the ultrathin graft: the first one is used to debulk the corneal donor tissue and the second one to cut to the final thickness. This technique has the same indications as conventional DSAEK, it theoretically minimizes post-operative complications and has the improved visual outcomes and lower rejection rates of DMEK, but studies on how the donor lenticule thickness and visual outcomes are related have had contradictory conclusions    . A recent randomized multicenter clinical trial concluded that compared with DSAEK, UT-DSAEK resulted in faster and better visual recovery with similar refractive outcomes, endothelial cell loss and incidence of complications. Nevertheless, nowadays surgeons tend to prefer thinner grafts, despite the fact that they can be more difficult to manipulate intraoperatively.
- Boyd K, DeAngelis KD. Iridocorneal Endothelial Syndrome . American Academy of Ophthalmology. EyeSmart® Eye health. https://www.aao.org/eye-health/diseases/iridocorneal-endothelial-syndrome-5. Accessed March 14, 2019.
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