Deep Anterior Lamellar Keratoplasty as an Alternative to Penetrating ...

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Ophthalmology Volume 118, Number 1, January 2011procedures include deep lamellar EK, Descemet’s stripping(automated) EK (DSEK or DSAEK), Descemet’s membraneEK, and Descemet’s membrane automated EK. Thehealth of the corneal endothelium is the main criterion fordeciding if an anterior or posterior LK procedure is indicated.Diseases involving the corneal endothelium can bemanaged with EK or PK, and those diseases involving boththe corneal endothelium and the corneal stroma usuallyrequire PK. In conventional anterior LK, only a portion ofthe corneal thickness is replaced.The first successful human partial penetrating cornealtransplant was performed by Zirm 1 in 1905 using aspring-driven trephine originally designed by von Hippel2 in 1888 for performing partial LK. Over the last halfof the 20th century, PK became the standard of care formanaging the surgical correction of most axial diseasesof the cornea. Lamellar keratoplasty was usually reservedfor the tectonic surgical correction of less common cornealconditions, such as peripheral ectasias, perforatedulcers, and traumatic loss of tissue. However, there hasalways been a cadre of ophthalmic surgeons, includingPaufique, 3 Malbran, 4 Anwar, 5 and others, who have usedlamellar corneal transplant surgery as an alternative toPK for the optical correction of axial corneal diseaseswith normal corneal endothelium, such as keratoconus,stromal corneal dystrophies, and corneal scars from traumaticinjury or infection. In the 1970s, there was increasedinterest in lamellar corneal transplantation. 6 As aresult of the technical difficulty of the procedure and thereduced postoperative acuity typically following LK,however, PK has remained the dominant corneal transplantprocedure for the optical correction of cornealdisease.There has been increased interest in newer anteriorlamellar corneal procedures for vision restoration, asnoted by publications in peer-reviewed journals, articlesin industry-supported publications, and instructionalcourses both in private venues and at educational meetingsof ophthalmological organizations. One of the mostpublicized of the various anterior lamellar corneal procedures,DALK, involves the removal of central cornealstroma while leaving host corneal endothelium and Descemet’smembrane (DM) intact. Descemet’s membranemay or may not be exposed in DALK procedures. Themajor theoretic advantages of DALK over PK proceduresare the absence of potential corneal endothelial cell immunerejection and the expected retention of most recipientcorneal endothelial cells in DALK surgery comparedwith the rapid decrease in donor corneal endothelial celldensity (ECD) after PK surgery.Several surgical techniques have been developed to accomplishremoval of all, or almost all, of the corneal stromain a lamellar dissection bed, which is the most critical aspectof a successful DALK. A brief overview of DALK techniqueswill be summarized in this article.When Sugita and Kondo 7 first presented their techniquefor baring DM, they called the technique “deep anteriorlamellar keratoplasty,” or DLK. Because that term laterbecame widely used to refer to the diffuse lamellar keratitisassociated with LASIK surgery, in this assessment the abbreviationDALK is used to refer to deep anterior LKprocedures in general. Anwar and Teichmann 8 suggestedthat the term “maximum depth anterior lamellar keratoplasty”be used to refer to baring of DM. In this assessment,the terms “DALK” and “maximum depth DALK” (MD-DALK) are used. The literature does not always distinguishbetween cases in which DM baring was planned (i.e., MD-DALK) but not achieved because of perforation, surgeoncaution, and so forth, and cases in which enough deepcorneal stroma was left in the surgical bed to qualify as aDALK but not as an MD-DALK. In other techniques thatare discussed, DM exposure is not the goal of the DALK,although DM exposure is occasionally achieved, and thisdistinction is not usually identified.The perimeter of the DALK bed is usually defined usinga trephine diameter of 7 to 8.5 mm to partially cut throughthe anterior stromal fibers, but not deep enough to enter theanterior chamber, depending on the host corneal diameterand the corneal disease being treated. This partial-thicknesstrephination may be performed initially, as in the hydrodelaminationtechnique of Sugita and Kondo 7 or the big-bubbletechnique of Anwar and Teichmann; 9 after expansion of thecorneal stroma with air, as in the air injection technique ofArchila, 10 as modified by Morris et al 11 and Coombes etal; 12 or after the limbal dissection of a deep lamellar pocketthat is then filled with an ophthalmic viscosurgical device(OVD) using the Melles technique. 13Sugita and Kondo’s 7 method of direct dissection afterpartial trephination involves removal of the anterior twothirds of corneal stroma, followed by injection of fluid intothe remaining stromal bed and spatula delamination forremoval of the deeper stromal layers. This is followed byhydrodelamination and exposure of DM in the central 5 mmof the trephine bed. Rostron’s direct dissection methodinvolves expanding the corneal thickness with air injectionbefore trephination and then removing the overlying stromaby direct dissection. If DM is detached during the airinjection, all overlying stroma will be removed. As doSugita and Kondo, Anwar first performs a partial-depthtrephine cut but then forcibly injects air deep in the stromalbed to detach DM, producing a “big bubble” that greatlyfacilitates the removal of all stroma in the trephine bed. Thedirect dissection DALK techniques using air or fluid oftenresult in baring of DM. Sugita and Kondo’s techniquerequires peeling off the final thin layer of deep stroma, atleast in the central 5 mm or so, whereas the big-bubbletechnique, when successful, results in separation of DMfrom the deep corneal stroma. Otherwise, layer-by-layerdeep dissection with the aid of air, fluid, or an OVD may berequired to attempt DM exposure.The Melles technique requires a limbal approach anddepends on the surgeon’s visual determination of the depthof the lamellar dissection. A full-corneal diameter pre-DMpocket is created by lamellar dissection and filled with anOVD, and then trephination is performed to remove theanterior stromal button. The thickness of the residual stromalbed is dependent on the surgeon’s ability to judgevisually how close the lamellar dissection blade can come toDM without puncturing it.210
Reinhart et al Deep Anterior Lamellar KeratoplastyRostron’s DALK procedures generally use fullthickness,lyophilized donor lenticules, whereas Sugita andKondo’s 7 earlier efforts used cryolathed lenticules. Glycerin-cryopreservedcorneal tissue has also been acceptable. 14One study specifically compared eyes that had receivedlyophilized donor corneas or donor corneas kept in OptisolGS (Bausch & Lomb, Inc., Rochester, NY) and found nostatistical differences between the 2 methods of donor cornealpreservation. 15 According to the recent literature, mostsurgeons use full-thickness donor lenticules obtained fromcorneal sclera rims preserved in intermediate storage media(e.g., Optisol GS) or organ culture media, as is common inEurope. The donor endothelium can be removed with a drysurgical sponge. However, many surgeons also remove DM.In either case, the posterior face of the donor graft will havea smooth interface apposed to the smooth bed of the exposed(bared) host DM. The antigenic load of the donor isalso decreased by removing the endothelial cells. In DALKprocedures where some residual stroma remains, the interfacewill not be as regular, and presumably even less regularif the donor lenticule has also been obtained through surgicaldissection, such as described by Tsubota et al 16 andPanda et al. 17Question for AssessmentThe objective of this assessment is to address the followingquestion: How does DALK compare with PK for the outcomesof BSCVA, refractive error, rejection, and graftsurvival?Description of EvidenceA search of the peer reviewed English-language literaturewas conducted in the PubMed database on December 14,2006, and October 1, 2007, and a search of the CochraneLibrary database was conducted on December 18, 2006, andOctober 1, 2007, limited to citations starting in 1997. Keywords in the search were the MeSH heading corneal transplantationcombined with text words deep anterior lamellarkeratoplasty or DALK or deep lamellar keratoplasty orDescemet’s membrane baring or maximum depth anteriorlamellar keratoplasty. The authors assessed the 236 citationsresulting from the electronic searches and selected 88citations that definitely or potentially met the inclusioncriteria.The authors obtained the full copy of these 88 articles forfurther assessment. The reviewers were not masked to trialresults or publication details. The authors reviewed the full textof these articles to assess their inclusion according to theselection criteria. One additional article was identified fromreview of an article reference list. The authors selected 42articles for methodological review, and they chose an additional19 articles to send to the first author for assistance inwriting the first draft. These 19 articles were review articles,single-case reports of complications, or single-case reports oftechnique, and they did not receive methodological review.The methodologist assigned ratings of level of evidenceto each of the selected articles. A level I rating was assignedto well-designed and well-conducted randomized clinicaltrials; a level II rating was assigned to well-designed casecontroland cohort studies or poor-quality randomized clinicaltrials; and a level III rating was assigned to case series,case reports, and poor-quality case-control or cohort studies.Two studies were randomized controlled trials that wererated as level II evidence because of insufficient power, lackof masking, and a less rigorous randomization method. 15,18All other articles were comparative and noncomparativecase series, prospective and retrospective, or case reportsand were rated as level III evidence.An updated search, conducted on May 28, 2009, includedthe additional search term penetrating keratoplasty(MeSH and text) and retrieved 788 citations, of which anadditional 73 possibly relevant studies were identified andreviewed. Of these, 13 were judged relevant. In addition,surveillance of the literature identified more recent relevantpublications. These additional studies were rated as level IIIevidence.Published ResultsDetailed descriptions and Tables (1–6) of the outcomesfrom the included studies are included in the Appendix(available at http://aaojournal.org).Eleven published studies were identified in which theoperative and postoperative results of DALK and PK procedureswere compared directly. Only 1 study 18 was assigneda level II rating, and the other 10 studies were ratedas level III. All were single-institution studies, often withone operative surgeon, and attempts were made to controlfor common factors such as diagnosis or age. These 11studies are particularly useful for comparing the visual,refractive, early postoperative ECD results, and surgicalcomplications of the 2 procedures. These data are presentedin Table 1 (available at http://aaojournal.org). The DALKdata from 10 of these 11 studies were then abstracted andcompiled along with DALK data from 31 other clinicalstudies (1 study rated as level II and 30 rated as level III) toobtain a broader view of the operative complications ofDALK, as well as postoperative visual, refractive, and ECDdata. The results of those 41 studies are presented, in part,in Table 2 (available at http://aaojournal.org).The 11 identified clinical comparative DALK/PK studiesinclude data on a total of 481 eyes that had DALK and 501eyes that had PK. Eight studies had 26 eyes in eachgroup, 17–24 one study had 41 DALK and 43 PK eyes, 25 onestudy had 135 DALK and 76 PK eyes, 26 and one study had150 in each group. 27 Seven of the studies 19–24,26 enrolledonly patients with keratoconus, one study enrolled onlypatients with lattice or macular corneal dystrophy, 25 and theremaining 3 studies included various corneal stromaldiseases. 17,18,27Table 3 (available at http://aaojournal.org) lists the reportedcomplications for the 1843 eyes in the 41 studies forplanned DALK procedures only. The most common operativecomplication was DM perforation(s), which occurredin 11.7% of cases. Air or gas injections into the anteriorchamber at the time of surgery or in the postoperative period211
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