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Randomized controlled trials would settle question of ‘best’ endothelial keratoplasty technique
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Endothelial keratoplasty has revolutionized corneal transplantation surgery in the last decade. For my country, the Netherlands, around 50% of all transplantation procedures are now endothelial keratoplasties. Descemet’s stripping automated endothelial keratoplasty, in which a microkeratome is used to prepare the endothelial transplant, has become the procedure of choice for treating corneal endothelial dysfunction, essentially replacing penetrating keratoplasty for this indication. The main advantages of DSAEK over PK include faster visual rehabilitation, minimal surgically induced astigmatism, improved postoperative corneal astigmatism and preservation of biomechanical properties.
After DSAEK, however, most eyes do not achieve 20/20 despite clear postoperative corneas and otherwise healthy eyes. The presence of stromal irregularities has been suggested to degrade the optical and refractive quality after DSAEK. Descemet’s membrane endothelial keratoplasty, in which the stroma portion of the donor is eliminated, currently appears to provide the fastest and best visual recovery of all endothelial keratoplasty techniques. However, manual donor preparation is challenging, and handling the extremely thin DMEK graft is difficult, leading to higher rates of graft dislocation.
Thinner DSAEK grafts have been suggested to achieve better vision. This proposed relationship is particularly relevant because graft thickness can be influenced by the choice of microkeratome head. However, preparation and handling of thinner grafts is not without challenges, and recent studies on the relationship between lenticule thickness and visual outcome show conflicting results.
In a recent study, we examined the relationship between central graft thickness measured by anterior segment optical coherence tomography and visual gain following DSAEK. We found that the gain in visual acuity was significantly correlated to graft thickness. We also found that thicker grafts were associated with greater asymmetry of the posterior corneal surface. Thick grafts have been suggested to magnify the curvature mismatch between donor and recipient, resulting in the formation of stromal folds when donor stroma fits against that of the recipient and leading to a worse visual outcome. The holy grail, therefore, is the safe preparation of a thin graft that can provide excellent recovery of vision.
The question is whether the major advantage of DMEK, ie, the increased visual gain of on average one Snellen line, according to most experts, outweighs the disadvantages of DMEK, including a significant learning curve, donor tissue loss with preparation, high percentages of graft dislocation (up to 50%) and difficulties in handling in very edematous recipient corneas. Especially in countries where donor tissue is scarce, any loss of donor material during the preparation process or an initial increase in primary graft failure has to be balanced against the well-established track record of DSAEK. Recently, modifications in cutting technology (mechanical double-pass or combination with femtosecond laser technology) have led to the production of ultra-thin lamellar grafts, which are said to provide better visual acuity. Innovative mechanical microkeratome technology may even facilitate single-pass ultra-thin DSAEK grafts with a thickness of 75 µm to 100 µm (after organ culture storage) and a standard deviation of only around 20 µm. Currently, the focus is on precut tissue that will lead to a significant reduction in surgical time, less investment costs in microkeratomes and therefore a better cost-effectiveness of the procedure. Unfortunately, none of the existing femtosecond laser systems so far has been able to produce ultra-thin lamellar grafts that can match the visual outcome of grafts produced with mechanical microkeratome technology.
For the general ophthalmological community and the decision makers in health care, it is necessary to point out the advantages and disadvantages of the various endothelial keratoplasty techniques. The only way to address this appropriately is through evidence-based medicine. In another important field of corneal surgery, ie, treatment of keratoconus progression by corneal cross-linking, the lack of well-designed randomized clinical trials has led to reluctance with health care authorities such as government and insurance companies to accept this treatment methodology as an evidence-based proven procedure. Consequently, in many European countries, no reimbursement exists for corneal cross-linking.
The only way to address the question, “Which type of endothelial keratoplasty is ‘best?’” is by designing randomized controlled trials that will define the safest and most efficacious and cost- effective treatment. Only then will we be able to counsel our patients in an intelligent way regarding realistic outcomes and expectation patterns and provide reliable information to health care authorities for reimbursement strategies.
- For more information:
- Rudy Nuijts, MD, PhD, and Mor M. Dickman, MD, can be reached at University Eye Clinic Maastricht, Department of Ophthalmology, P.O. Box 5800, 6202 AZ Maastricht, Netherlands; +31-43-3877344; fax: +31-43-3875343; email: rudy.nuijts @mumc.nl; mor.dickman@mumc.nl.
Disclosure: No products or companies are mentioned that would require financial disclosure.