Peter W. Madden

Silk fibroin in ocular tissue reconstruction

The silk structural protein fibroin displays potential for use in tissue engineering. We present here our opinion of its value as a biomaterial for reconstructing tissues of clinical significance within the human eye. We review the strengths and weaknesses of using fibroin in those parts of the eye that we believe are most amenable to cellular reconstruction, namely the corneoscleral limbus, corneal stroma, corneal endothelium and outer blood-retinal barrier (Ruyschs complex). In these areas we find that by employing the range of manufacturing products afforded by fibroin, relevant structural assemblies can be made for cells expanded ex vivo. Significant questions now need to be answered concerning the effect of this biomaterial on the phenotype of key cell types and the biocompatibility of fibroin within the eye. We conclude that fibroins strength, structural versatility and potential for modification, combined with the relative simplicity of associated manufacturing processes, make fibroin a worthy candidate for further exploration.

Evaluation of Eph receptor and ephrin expression within the human cornea and limbus

Eph receptor tyrosine kinases and their ligands, the ephrins, regulate the development and maintenance of multiple organs but little is known about their potential role within the cornea. The purpose of this study was to perform a thorough investigation of Eph/ephrin expression within the human cornea including the limbal stem cell niche. Initially, immunohistochemistry was performed on human donor eyes to determine the spatial distribution of Eph receptors and ephrins in the cornea and limbus. Patterns of Eph/ephrin gene expression in (1) immortalised human corneal endothelial (B4G12) or corneal epithelial (HCE-T) cell lines, and (2) primary cultures of epithelial or stromal cells established from the corneal limbus of cadaveric eye tissue were then assessed by reverse transcription (RT) PCR. Limbal epithelial or stromal cells from primary cultures were also assessed for evidence of Eph/ephrin-reactivity by immunofluorescence. Immunoreactivity for ephrinA1 and EphB4 was detected in the corneal endothelium of donor eyes. EphB4 was also consistently detected in the limbal and corneal epithelium and in cells located in the stroma of the peripheral cornea. Expression of multiple Eph/ephrin genes was detected in immortalised corneal epithelial and endothelial cell lines. Evidence of Eph/ephrin gene expression was also demonstrated in primary cultures of human limbal stromal (EphB4, B6; ephrinA5) and epithelial cells (EphA1, A2; ephrinA5, B2) using both RT-PCR and immunofluorescence. The expression of Eph receptors and ephrins within the human cornea and limbus is much wider than previously appreciated and suggests multiple potential roles for these molecules in the maintenance of normal corneal architecture.

Standard terminology and labeling of ocular tissue for transplantation.

Purpose: To develop an internationally agreed terminology for describing ocular tissue grafts to improve the accuracy and reliability of information transfer, to enhance tissue traceability, and to facilitate the gathering of comparative global activity data, including denominator data for use in biovigilance analyses. Methods: ICCBBA, the international standards organization for terminology, coding, and labeling of blood, cells, and tissues, approached the major Eye Bank Associations to form an expert advisory group. The group met by regular conference calls to develop a standard terminology, which was released for public consultation and amended accordingly. Results: The terminology uses broad definitions (Classes) with modifying characteristics (Attributes) to define each ocular tissue product. The terminology may be used within the ISBT 128 system to label tissue products with standardized bar codes enabling the electronic capture of critical data in the collection, processing, and distribution of tissues. Guidance on coding and labeling has also been developed. Conclusions: The development of a standard terminology for ocular tissue marks an important step for improving traceability and reducing the risk of mistakes due to transcription errors. ISBT 128 computer codes have been assigned and may now be used to label ocular tissues. Eye banks are encouraged to adopt this standard terminology and move toward full implementation of ISBT 128 nomenclature, coding, and labeling.

Replacement of the Corneal Endothelium and the Conceptual Framework for an Artificial Substitute

Dysfunction of the corneal endothelium due to cell loss caused by aging, disease or trauma can lead to severe visual impairment and blindness. Traditionally, dysfunctional endothelia are managed surgically, by removing the entire central cornea and transplanting either donor corneal tissue (penetrating keratoplasty), or just endothelia isolated from donor corneas. As in many cases it is only the corneal endothelium requiring replacement, many attempts were made over the last decades to develop an endothelial substitute, thereby precluding the need for the use of full donor corneas. This article reviews these attempts, which include artificial membranes, cell-coated corneal transplants, and cell-coated membranes. The presumption of an artificial corneal endothelium capable of duplicating the transendothelial ion-and-fluid transport function is examined in light of the latest hypotheses regarding the mechanism of this function.

Potential Effect of Excluding Variant Creutzfeldt-Jakob Disease on the Eye Donor Pool in Australia

Purpose: To quantitate the likely effect on the available eye donor pool by excluding potential donors who may have had exposure to variant Creutzfeldt-Jakob disease by virtue of spending time in countries where bovine spongiform encephalopathy (BSE) is endemic. Methods: A telephone survey by systematic sampling from the Brisbane phone directory was undertaken to ascertain the number of potential donors who had resided in the United Kingdom and in other countries. Results: Between 19% of potential donors would have had to have been excluded by virtue of residing in the United Kingdom for >6 months between 1980 and 1996 and 29% for those who had traveled to any other country in which BSE was identified. Conclusions: This study suggests that adopting an eye bank policy of excluding donors potentially exposed to BSE would have a significant effect on donor numbers. Health departments and eye banks will need to weigh the small additional protection from such policy decisions against the likely effect on corneal tissue supply.