BLOG: Surgeon’s mantra: Replace what’s needed, do it gently
A few years ago, the field of retina underwent a revolution with newer, gentler ways of treating macular degeneration with injections instead of laser. Corneal transplantation is undergoing a similar revolution now, and the overarching theme is that we replace only the defective portion of the cornea using ever-improving, ever-gentler techniques. Gone are the days of when a penetrating keratoplasty was a cure-all for every type of corneal disease.
To treat the corneal surface, we used to do far more tarsorrhaphies, conjunctival flaps and limbal allograft transplants. Now, non-healing defects frequently benefit from amniotic membrane grafts, and self-retaining membranes like the AmbioDisk from Katena and Prokera from Bio-Tissue have become routine practice. Furthermore, liquid preparations of amniotic membrane are in development, and amniotic cytokine extract is now commercially available. Along with serum tears and Dompé’s Oxervate (cenegermin) recently approved to treat neurotrophic ulcers, these offerings will likely reduce the need for more advanced and irreversible surgical therapies. Both patients and surgeons couldn’t be happier.
Corneal stromal disease also represents a particular challenge. Deep anterior lamellar keratoplasty has gained much traction over penetrating keratoplasty, and I have personally found Mark Vital’s “grip and rip” technique to be simple, reproducible and teachable. Furthermore, synthetic corneas like the products from KeraMed and CorNeat and even 3-D bioprinted “tissue” show promise for cases that are not amenable to human tissue transplantation. The two biggest challenges with previous synthetic corneas like the Boston keratoprosthesis have been corneal melting around the prosthesis and long-term development of glaucoma, which can be very difficult to assess and manage. Time will tell if newer synthetic corneas can avoid these vulnerabilities. In general, replacing human corneal tissue with synthetic material has been a most humbling science.
Innovations in replacing the inner endothelial layer of the cornea have been most impressive. Endothelial keratoplasty is now performed almost twice as frequently as penetrating keratoplasty in the U.S., with Descemet’s stripping endothelial keratoplasty now representing about 25% of those endothelial procedures. This technique, which just transplants Descemet’s membrane with endothelial cells, has a challenging learning curve, so many surgeons are optimistic about easier, newer techniques being developed in Japan and Germany, where cultured human endothelial cells are injected or transplanted onto the recipient in sheets.
As our cover story in this issue of OSN highlights, addressing the global demand for corneal transplant is a daunting problem that demands new thinking; our current supply chain of corneas cannot possibly meet the demand. These new techniques, if they can be scaled to provide a supply chain of tissue to local surgeons trained in easy-to-adapt techniques, will mean new life for hundreds of thousands of patients currently suffering from corneal blindness throughout the world.
Disclosure: Hovanesian reports he is a consultant to CorneaGen and Katena.