Posterior Corneal Procedures

Posterior Lamellar Keratoplasty & Deep Lamellar Endothelial Keratoplasty

Posterior lamellar keratoplasty is a surgical procedure that involves replacement of diseased posterior cornea with donor tissue while retaining the anterior corneal layers (Figure 1). The aim is to replace only the dysfunctional endothelial layer with healthy functioning endothelium, thus allowing for the clearing of the corneal edema.

In an early approach, Melles et al. described an approach to deep lamellar endothelial keratoplasty (DLEK),^[97] in which intraocular air was used to support the donor tissue so as to avoid problems associated with corneal sutures. This technique was later modified by Terry and Ousley.^[181]

Many series have confirmed that endothelial keratoplasty produced viable postoperative endothelial cell count, did not induce corneal refractive changes, reduced astigmatism rates, and provided for earlier refractive stability and visual rehabilitation compared with conventional PKP surgery.^[182–190] However, the average Snellen visual acuity attained was approximately 20/40–20/50, with few 20/20 results.^[182–190] The limitation in postoperative visual acuity was thought to be likely due to the uneven donor–host interface. Descemet stripping and endothelial keratoplasty (DSEK) was then created with the aim to provide a smoother recipient bed.

DSEK & Descemet Stripping Automated Endothelial Keratoplasty

Melles et al. again revolutionalized the field by instituting a significant modification to the endothelial keratoplasty procedure. They described a technique, termed descemetorhexis, to strip away the DM from a recipient cornea in order to provide a smoother recipient interface.^[191] Price and Price popularized the technique in the USA, referring to it as DSEK (Figure 7).^[192–194]

Figure 7.

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Descemet Stripping and Endothelial Keratoplasty Versus Penetrating Keratoplasty. (A) Visante optical coherence tomography view of the corneal post-Descemet stripping and endothelial keratoplasty, and (B) post-penetrating keratoplasty.

In DSEK, the donor corneal tissue is prepared as in endothelial keratoplasty. The cornea is dissected at 90% stromal depth in an artificial anterior chamber filled with air, using the technique described by Melles et al. (see posterior lamellar keratoplasty and DLEK).^[195] The center of the cornea is marked and a full-thickness button is made by trephination.

The technique used by Price and Price for the recipient cornea is also similar to the DLEK surgery, except DM stripping is performed rather than posterior stromal dissection and removal.^[192,194] The corneal epithelium is first marked to outline the area from which DM was to be removed. Through a temporal scleral tunnel as originally described,^[192,194] or a limbal or clear corneal incision similar to cataract surgery,^[196] the DM is scored along the perimeter of the area to be removed with a Price–Sinskey hook. Within this circumscribed area, the DM and diseased endothelium is then carefully stripped off the posterior stroma using a Descemet’s stripper and removed from the anterior chamber with forceps. The anterior corneal tissue of the donor button is removed and a small amount of viscoelastic is placed on the donor endothelium. The donor posterior lamella is folded on itself in a ‘taco’ configuration and placed into the recipient anterior chamber. The donor taco is unfolded and centered, and the temporal scleral incision is closed with one or more sutures. Air is injected into the anterior chamber and left there for 5–8 min to promote donor tissue adherence. The ocular surface is massaged with a Lindstrom LASIK flap roller or a similar instrument while the anterior chamber is filled with air to help remove any residual fluid trapped in the donor–host interface. After the massage, three or four equally spaced small stab incisions are placed in the midperipheral recipient cornea down to the graft interface to drain residual trapped fluid. Most of the air in the anterior chamber is then removed and replaced with balanced salt solution, leaving a small air bubble. Patients are then instructed to lie facing the ceiling for 30–60 min to allow the remaining air to push the donor tissue against the recipient cornea.

In 2006, Gorovoy modified DSEK by replacing the manual stromal dissection of the donor cornea with an automated keratome dissection.^[197] He termed this modification Descemet stripping automated endothelial keratoplasty (DSAEK). As this method avoids all manual lamellar dissections, Gorovoy hypothesized that the resulting smoother donor–host interface may decrease visual recovery time and increase visual quality. This hypothesis was confirmed by other authors.^[198,199] However, the higher donor dislocation rate originally found by Gorovoy^[197] was also echoed in the literature.^[199]

Current literature suggests that DSAEK appears to be effective for the treatment of endothelial diseases of the cornea.^[200] Some reports have even suggested that DSAEK should replace traditional PKP for surgical treatment of endothelial disease^{[199,201,202]} as it seems to be similar to PKP in terms of surgical risks and complication rates,^[199,203] graft survival (graft clarity) and acuity,^[204–206] and endothelial cell loss;^{[201,204,207,208]} and superior to PKP in terms of early visual recovery and refractive stability,^{[202,209–211]} postoperative refractive outcomes,^{[199,212–215]} wound and suture-related complications^[216], and intraoperative and late choroidal hemorrhage risk.^{[203,217,218]} A recent report by the American Academy of Ophthalmology concluded that the four most common complications of DSAEK are graft dislocation (Figure 8), endothelial rejection, graft failure and glaucoma, all of which do not seem to be detrimental to the ultimate visual recovery in most cases.^[200] The report also stated that, as in any new technique, long-term prospective studies are needed to demonstrate acceptable complication rates and long-term endothelial cell survival post-DSAEK.

Figure 8.

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Post-Descemet Stripping and Endothelial Keratoplasty. (A) Donor lamella dislocation day 1 post-Descemet stripping and endothelial keratoplasty (DSEK). Air bubble still visible in AC. (B) Post-DSEK. Central clear cornea overlying the healthy donor endothelium. Courtesy of Jeffrey Judelson (University of Saskatchewan, SK, Canada).

DM Endothelial Keratoplasty

In 2002, Melles et al. reported a human cadaver eye model in which the DM carrying healthy endothelial cells was transplanted through small scleral tunnels.^[219] He subsequently termed the technique DM endothelial keratoplasty (DMEK) and reported its use in a patient with Fuchs’ endothelial dystrophy.^[220]

The donor tissue used in Melles’ et al. DMEK was cultured for 2 weeks before trephination and subsequent DM stripping with microforceps. Because of the elastic properties of the membrane, a ‘DM roll’ spontaneously formed with endothelium at the outer side. The DM roll was stored in organ culture medium until the time of transplantation. Melles then performed a procedure similar to DLEK (Melles’ technique), substituting the posterior stromal dissection in the recipient cornea with a descemetorhexis.^[191] The donor DM roll was sucked into a custom-made injector after being stained with trypan blue. The roll was inserted into the recipient anterior chamber using the injector and gently spread out. Air was injected underneath the donor DM to oppose the tissue onto the recipient cornea. The anterior chamber was completely filled with air for 30 min, after which the air was replaced with liquid.^[220] The patient’s visual acuity was reported to be 20/80 at 1 day and 20/20 at 1 week post-transplantation with no change in refraction.

Unlike other EK procedures, DMEK provides a near-normal restoration of the grafted cornea, which may result in faster and more complete visual rehabilitation.^[219] Without the additional donor stroma, the visual performance of the eye is likely to be limited only to the preoperative condition of the recipient anterior cornea. DMEK may also be more suitable for modern anterior segment surgery as, with the small donor DM roll, the procedure can easily be performed through a clear corneal incision as that used in cataract surgery. However, other surgeons have found that DM is quite fragile, and manipulations of donor tissue that are reasonably well tolerated in the other endothelial keratoplasty surgeries result in wrinkles, folds, tears and unacceptable endothelial cell loss when applied to pure DM transplantation. Various modifications of carriers have been used in an attempt to overcome these challenges.^[221,222]