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Surgical Strategies to Improve Visual Outcomes in Corneal Transplantation

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Surgical Strategies to Improve Visual Outcomes in Corneal Transplantation Eye (2014) 28, 196–201 & 2014 Macmillan Publishers Limited All rights reserved 0950-222X/14 www.nature.com/eye 1,2 CAMBRIDGE OPHTHALMOLOGICAL SYMPOSIUM Surgical strategies MS Rajan to improve visual outcomes in corneal transplantation Abstract rehabilitating patients who had lost their corneal transparency to infection, The recent years have brought about a sea degeneration, or dystrophy.1 Penetrating change in the field of corneal transplantation keratoplasty (PK), which involves whole- with penetrating keratoplasty being phased organ transplantation, has inherent problems to newer lamellar keratoplasty techniques for related to multiple sutures, high degrees of a variety of corneal pathology. Improved and induced astigmatism, increased risk of innovative surgical techniques have allowed endothelial rejection, and poor long-term graft selective replacement of diseased host survival.2–4 All these factors limit early visual corneal layers with pre-prepared healthy recovery and compromise long-term visual donor corneal lamellae for anterior corneal stability in patients undergoing penetrating disorders such as keratoconus and posterior keratoplasty.Therefore,recentyearshaveseen corneal disorders such as Fuch’s corneal considerable improvements in techniques endothelial dystrophy. The results of lamellar to overcome such limitations. Current techniques are encouraging, with rapid visual developments in lamellar keratoplasty have rehabilitation and vastly reduced risk of enabled partial-thickness corneal transplants immune-mediated transplant rejection. to selectively replace anterior or posterior The techniques of deep anterior lamellar corneal tissue depending on the type of keratoplasty and Descemet’s stripping 1Cornea Unit, pathology in order to allow early visual endothelial keratoplasty (DSAEK) continue Addenbrooke’s Hospital, rehabilitation and long-term stability.5,6 This to evolve with advent of femtosecond lasers Cambridge University article aims to describe the present trends in Hospitals NHS Trust, and newer concepts such as pre-conditioned lamellar keratoplasty and future strategies Cambridge, UK donor corneas for Microthin DSAEK and such as cell therapy that are being developed Descemet’s membrane keratoplasty. This 2 to address the growing demand for corneal Vision and Eye Research review describes the current developments in Unit (VERU), Anglia Ruskin transplantation. lamellar keratoplasty, including the futuristic University, Cambridge, UK approach using cell therapy to restore vision Correspondence: in corneal blindness. Lamellar keratoplasty MS Rajan, Consultant Eye (2014) 28, 196–201; doi:10.1038/eye.2013.279; Anterior lamellar keratoplasty (ALK) involves Ophthalmologist, Cornea published online 3 January 2014 Unit, Addenbrooke’s removal and replacement of the corneal stroma Hospital, Cambridge with preservation of the host endothelial layer, Keywords: DSAEK; corneal transplantation; university Hospitals NHS which provides long-term protection from lamellar keratoplasty; corneal endothelial trust, Hills Road, immune-mediated endothelial rejection. Cambridge CB2 0QQ, UK. keratoplasty; microthin DSAEK; corneal Although ALK has been practiced for several Tel: +44 (0)1223 257 168; surgery Fax: +44 (0)1223 274 810. years, recent innovations have allowed total E-mail: madhavan.rajan@ debulking of the corneal stroma in order to addenbrookes.nhs.uk improve visual outcomes following the Introduction procedure (Figure 1).6–8 Previous studies Received: 28 October 2013 Corneal organ transplantation remains the involving partial or subtotal removal of the Accepted in revised form: 21 November 2013 mainstay treatment for patients with corneal stroma for pathologies such as Published online: 3 January corneal blindness. Until recently, penetrating keratoconus and stromal dystrophies had not 2014 keratoplasty has been the gold standard for provided full visual recovery, although they Newer techniques in corneal transplantation MS Rajan 197 Figure 1 Schematic diagram of human cornea in a cross-section showing the stromal plane of dissection in Anterior lamellar keratoplasty (ALK), Pre-Descemet’s deep anterior lamellar keratoplasty (DALK), and Descemet’s barring DALK. Figure 2 Histophotograph of a human cornea showing (a) deeper stromal planes of dissection in Descemet’s and Pre-Descemet’s DALK, and (b) a scanning electron microscopy image of bare Descemet’s membrane (DM) with a smooth interfacing surface. were successful in retaining the host endothelium. achieve comparable visual and refractive results to The stroma–stroma contact, interface scarring, and penetrating keratoplasty, provided the residual excessive recipient host stroma were all implicated in recipient (host) stroma is no more than 20 um poor visual recovery in ALK. In comparison, the deep (Figure 2).9,10 These visual results were substantiated by ALK (DALK) procedures developed by Anwar a report by the American academy, in which 11 and Melles have paved the way for total or near-total published studies comparing DALK with PK were separation of the corneal stroma from the underlying analyzed.11 In addition, the graft survival of DALK Descemet’smembranebytheBigBubbletechniqueor corneal transplants was shown to be higher at 97% air-assisted deep lamellar dissection.7,8 Although at 5 years compared with 73% for penetrating Descemet’s barring procedures are technically keratoplasty in a separate study.12 Thus, current trends challenging, pre-Descemet’s dissection appears to favor DALK procedures over PK for corneas with Eye Newer techniques in corneal transplantation MS Rajan 198 stromal pathology and healthy host endothelium, with deep lamellar endothelial keratoplasty has undergone proven advantages of comparable visual and refractive significant improvements in surgical techniques to results to those of PK with improved long-term graft achieve selective replacement of the diseased endothelium survival. with a functional endothelial layer (Figure 3). Femtosecond-assisted keratoplasty DSAEK Femtosecond lasers have practically replaced The most commonly practiced procedure is Descemet’s microkeratomes for lamellar cuts in LASIK surgery. stripping automated endothelial keratoplasty (DSAEK), Similarly, femtosecond lasers have been used to perform in which a posterior donor lamella prepared with an vertical and deeper cuts to facilitate PK with variously automated microkeratome is inserted after stripping the shaped profiles to configure better wound apposition host Descemet’s membrane.19 There are several and reduce post-op astigmatism.13,14 Top hat, reverse hat, advantages compared with PK, which includes reduced mushroom, zig-zag, and christmas tree-shaped excisions post-op astigmatism, rapid visual recovery, and have been tested with moderate improvement in post-op improved graft survival.18 Graft detachment and astigmatism.15 Recently, femtosecond lasers have been primary graft failures in DSAEK show specific trends utilized to standardize the DALK procedure with compared with PK. During the learning curve, post-op some success.16,17 Developments in laser energy, detachment and primary failure were reported to be repetition rate, and cutting profiles are likely to improve between 5 and 80% and 3 and 29%, respectively.18,20 deeper ablations to improve DALK procedures, and it is Current studies show improving trends in both of these likely that femtosecond lasers will have an important role complications, with groups reporting less than 10% risk in the future of corneal lamellar transplantation with an of post-op graft detachment and a 5–8% risk of primary aim to achieve stronger graft–host interface, early suture graft failure.20 Surgeon experience and better tissue removal, and reduced induced astigmatism.6 handling techniques have contributed to the improved DSAEK outcome. In DSAEK, mean endothelial density Posterior lamellar keratoplasty loss appears to be between 13 and 54% in the first 6 Endothelial keratoplasty has replaced PK as the months.21,22 Graft rejection episodes following DSAEK gold standard procedure for corneal endothelial are fewer compared with PK and were typically reported dysfunction.18 The surgical technique originally termed as being between 10 and 12% at 2 years.23 Figure 3 Schematic diagram of the human cornea in a cross-section showing the three surgical methods in endothelial keratoplasty with varying graft thicknesses at 170 microns in (a). Descemet’s stripping automated endothelial keratoplasty (DSAEK) compared with 80 microns in Micro-thin DSAEK (b) and 20 microns in Descemet’s membrane endothelial keratoplasty (DMEK) (c). Eye Newer techniques in corneal transplantation MS Rajan 199 Thin DSAEK technique to successfully achieve significantly thinner DSAEK grafts by controlling the thickness of donor Recent developments in endothelial keratoplasty have corneas by utilizing pachymetry-controlled stromal focused on techniques to standardize the thickness of dehydration before microkeratome dissection (Micro- endothelial grafts.24,25 Graft thickness in DSAEK has thin DSAEK).29 Theairflowdevice(CAMflow)utilized been reported to vary between 50 and 250 mm.26 for stromal dehydration is shown in Figure 4. These Endothelial graft thickness directly influences the techniques improve the predictability of achieving posterior radius of the curvature and, as per thick lens sub 100 mm endothelial graft thickness resulting in equation, increases the focal length, thereby decreasing increased percentage of eyes reaching their full visual the refractive
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