Corneal Transplantation

Biosynthetic corneal implants made of fish scale- derived collagen may in the near future provide a potentially safe and effective alternative to the implantation of human tissue to help address the current donor cornea shortage worldwide, report researchers. “It is still very early days, but the initial results in animal models show a lot of potential for fish scale-derived collagen matrix as a possible alternative for human donor corneal tissue,” Martine J Jager MD, PhD, told delegates attending the 2013 Congress of the European Society of Ophthalmology during a symposium organised by the Academia Ophthalmologica Internationalis.

Dr Jager, Leiden University Medical Center, Leiden, the Netherlands, said that the development of a viable artificial cornea would go some way towards addressing the current deficit of donor corneas. “Corneal blindness is still the second major cause of blindness in the world. There is a shortage in donor corneas for lamellar or perforating corneal transplants, and this is especially the case in developing countries. If you look at the deficit between available corneas and needed corneas in India, for example, we see just how acute the problem is,” she said. An ideal artificial cornea, said Dr Jager, would be one which was easy to obtain, easy to insert and cheap to produce. She said that the idea of using fish scales for this purpose is credited to Dr Julio Lin, whose research with the tilapia fish identified it as a potentially viable source of type-I collagen with an amino-acid composition very similar to humans. Through a complex process, the decalcified scales of the fish are stripped of their cells, leaving a collagen scaffold with properties similar to natural human cornea. Stem cells can then be cultured on the collagen scaffold to create a sheet of limbal-corneal epithelium for research as well as clinical transplantation.

Research performed by Dr Herbert van Essen in Leiden showed that the fish scale-derived collagen offers several inherent advantages as a potential material for artificial cornea. First, the transparency of the fish-scale derived collagen is very good and is comparable to human corneas. Studies conducted to measure light scatter and light transmission showed that the amount of scattered light was comparable to that seen in early cataract and the percentage of light transmission was similar to the transmission through the human cornea. The material is also suturable, although considerable care is needed in handling the collagen matrix to avoid tearing. Biocompatibility testing of the collagen matrix has also been largely positive in the rat model, said Dr Jager.

To test its tolerance in rodent eyes, three separate placement techniques were used: anterior lamellar keratoplasty (ALK), interlamellar corneal pocket (IL) and subconjunctivally. Implantation of the matrix as an ALK led to mild haziness only, not obscuring the pupil, despite the development of neovascularisation around the sutures. Interlamellar placement led to a moderate haze, partly obscuring the pupil, and to partial melting of the anterior corneal lamella. The subconjunctival group exhibited local swelling and induration, which decreased over time. Histology showed a chronic inflammation varying from mild and moderate in the ALK- and interlamellar group, to more severe in the subconjunctival group, said Dr Jager. Going forward, Dr Jager said that further clinical studies are necessary for better understanding of the immunogenicity of the matrix and to resolve problems of mechanical irritation induced by some of the initial transplants in animal models.