Advances in Corneal Surgery
Recent advances in refractive surgery have catapulted our capabilities to perform traditional corneal disease surgery. The marriage of these two surgical procedures has heightened our ability to provide patients with better visual outcomes: The biggest advance in corneal transplantation over the past 10 years has been the move towards selective replacement of diseased corneal layers.
Before the past decade, most corneal disease states including corneal scars, diseases of the endothelium (eg, Fuchs dystrophy) and keratoconus were treated with full-thickness penetrating keratoplasty (PK). Now, we can selectively transplant the diseased layer of the cornea. Compared with full-thickness PK, the advantages of selective transplantation include less chance of rejection, due to the transplantation of lower tissue volume, and quicker rehabilitation times, where the use of fewer or no sutures induces less astigmatism.
Because we can identify and transplant the specific diseased layer, we may offer patients a variety of operations to correct their dysfunction. For example, excimer laser ablation may be used on patients with a superficial corneal opacity from a scar. If the scar is deeper (ie, involving the anterior half of the cornea), a lamellar keratoplasty (Figure 1) rather than a full-thickness transplantation may be used. In the case of a disease of the endothelium, like in Fuchs dystrophy, the endothelium may be replaced instead of the full-thickness transplantation. Lasers may also be used to treat astigmatism. Irregular astigmatism may be treated with surface ablation and regular astigmatism may be treated using a femtosecond laser.
One thing in particular that many surgeons are talking about in the field of corneal surgery is Descemet's stripping automated endothelial keratoplasty (DSAEK) (Figure 2). The use of anterior chamber maintainers and microkeratomes have familiarized us with automated lamellar surgery, which has helped make DSAEK more predictable and reproducible to preparing the donor tissue and implant the endothelial cells relatively atraumatically.
The other new and exciting advance, even for patients who require a full-thickness transplant, is the femtosecond laser. In the United States and Europe, the Intralase (Intralase, Irvine, California) has been approved for making incisions in the cornea and has been used for therapeutic keratoplasty. Rather than using a conventional handheld trephine, the laser precisely cuts the donor and recipient so that they match nicely. Customization of the trephination shape is also possible with the femtosecond laser. Early data with the Intralase femtosecond laser showed that using a top-hat configuration (Figure 3) for the donor and the recipient buttons allowed a better fit as well as potentially better wound stability and potentially quicker rehabilitation.1 Sutures may be removed earlier than with conventional keratoplasty. Femtosecond laser use is in its early stages, as mostly clinical investigators in the United States and Europe have had access to the technology.
IMMUNOSUPPRESSANTS
Ocular surface reconstruction is also a recent advancement that deserves notice. Over the last 10 to 15 years, the use of immunosuppressants (eg, mycophenolate mofetil [Cellcept; Roche Pharmaceuticals, Nutley, New Jersey], tacrolimus [Prograf; Astellas Pharma US, Deerfield, Illinois] and cyclosporine) emerged. Mycophenolate mofetil and tacrolimus are both systemic immunosupressants. We now also use amniotic membrane for conditions such as exceptionally vulnerable ocular surfaces, persistent epithelial defects and nonhealing corneal ulcers. We have learned much about limbal stem cell transplantation; systemic immunosuppression is absolutely critical for the success of this kind of surgery.
Advances are not only in corneal surgery technology. There is also hope for synthetic corneal prosthesis surgery. This may open the door for many patients who previously were not candidates due to cornea donor shortages. Although donor corneas are abundant in the United States, there are shortages in some parts of Europe and worldwide.
No matter how far we come with technological advances in corneal surgery, research will always be important. We must continue to research corneal immunology and our ability to prevent corneal donor tissue rejection. Donor rejection may depend upon the reason for transplantation, immune status and age. Remember to identify risk factors including previous transplants, the presence of blood vessels and a younger age. Younger patients live with the transplanted cornea for a longer time and therefore have an increased risk of rejection in their lifetime. It may not doom their graft to failure, however, it puts them at higher risk. Children are notorious for having transplant graft rejections because of their active immune systems.
In the future, I would like to see an abundant availability of corneal tissue so that it would never be the limiting factor for corneal rehabilitation. Further work with synthetic corneas may provide the same outcome as a regular human cornea. Corneal donor rejection remains a significant cause for graft failure, which is why further research on corneal immunology is needed. There are many unanswered questions as to why some people are prone to developing rejection. We must determine what factors we can control to prevent rejection. Finally, I would like to see quicker patient rehabilitation times. For a full-thickness corneal transplant, it may take 6 or 12 months before the patient is visually rehabilitated. That is potentially problematic for one-eyed patients or elderly patients where 6 to 12 months can be a long time. With these and more corneal surgery advances, we should be able to provide our patients with quicker rehabilitation times sooner rather than later.
Sonia H. Yoo, MD, is an associate professor of clinical ophthalmology at the Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, in Florida. Dr. Yoo states that she receives a travel stipend from Intralase. She may be reached at SYoo@med.miami.edu or +1 305-326-6322.
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