Corneal transplantation is the most widely practised form of clinical allografting. First successfully carried out almost a century ago, its place in clinical practice was well established before the vagaries of immunological privilege and allograft rejection were appreciated.

Early on, the cornea and anterior segment of the eye were established as ‘privileged sites’1 which led to a widely held view that corneal grafts were invariably successful. This is far from the truth.

Paradoxically, corneal transplantation is both the most successful and the least successful form of clinical transplantation. Grafts done for dystrophic conditions, particularly keratoconus, seldom reject, with a graft survival rate of 50% after 5 years. However, grafts done for acquired diseases fare badly.23 This is a great pity since acquired corneal blindness is second to cataract as a cause of visual loss on an international scale.4

The mechanisms of these frequent failures are many. Various factors account for the differences which are reflected in the wide variations in outcome seen between various centres. This variation is common in other branches of transplantation, is referred to as the ‘centre effect’, and defies specific elucidation.5

Dissecting out the various factors contributing to graft outcome demands extensive …