Edmund J. Lovett

Penetrating Keratoplasty in the Cat: A Clinically Applicable Model

A series of 28 consecutive penetrating keratoplasties were performed on adult cats. Donor corneas (n = 14) were maintained in culture medium for 14--24 hours prior to transplantation. Rotational autografts (n = 7) were used to control for cell loss caused by culture maintenance as well as for the effects of surgery. Additional homografts (n = 7) were transplanted following removal of the corneal endothelium to study the extent of host corneal endothelial cell regeneration. Pre- and post-operative endothelial cell counts of the homografts made from specular micrographs demonstrated an average cell loss of 30% one month following surgery. A similar 30% average cell loss was present in the rotational autografts. Clinically, both homografts and autografts remained clear and were near normal in thickness. Homografts lacking endothelium exhibited persistent, severe edema that correlated with the inability of the host corneal endothelium to resurface the graft. Clinical and morphologic evidence of mild homograft rejection as observed in 15% of the animals that received normal homografts. Corneal endothelial cell loss following penetrating keratoplasty in the cat approximates that observed following the same procedure in the human. Additionally, regenerative capacity of the corneal endothelium in the cat, like that of the human, is limited. These features suggest that this cooperative, hardy animal is an excellent model in which to study many aspects of corneal transplantation that have direct application to the treatment of human corneal disease.

Corneal Transplantation in the Cat: Cellular Immune Mechanisms in Graft Survival and Rejection

Systemic cellular immune suppression (measured in mixed-lymphocyte cultures) occurs after penetrating keratoplasty using homologous donor corneas in the feline model. These successful feline corneal grafts can be subsequently induced to reject, and the cellular immune suppression overcome by a second antigen challenge (skin graft). Heterologous (bovine) replacement endothelium, on the other hand, imposes so strong a donor-host incompatibility that any potential immunological suppression is overwhelmed and the transplants reject spontaneously. Thus, successful corneal transplantation depends on a balance of several factors that include systemic cellular immune responsiveness and donor-recipient antigen compatibility.