INTRARETINAL TRANSPLANTATION TO PREVENT PHOTORECEPTOR DEGENERATION

There is great interest in the potential of transplantation to treat r etinal degenerative diseases in humans; however, there are still funda mental questions to be addressed in experimental animal studies. We ha ve concentrated on two of these using the Royal College of Surgeons (R CS) rat as a suitable animal model. Firstly, does the loss of photorec eptors lead to secondary changes in the inner retina, which might comp romise any photoreceptor preservation strategy? Analysis has shown tha t there are not only histochemical changes in the inner plexiform laye r but also degeneration of retinal ganglion cells. The latter, occurri ng as a result of a vascular event, appears to have a parallel in some human retinal degenerative diseases. Secondly, what are the functiona l implications of the progressive photoreceptor loss in the RCS rat an d how may transplantation prevent or slow that process? A progressivel y enlarging visual field defect can be demonstrated in these rats whic h can be stabilized by transplantation of retinal pigment epithelial c ells. There is also a loss or diminished performance in a variety of v isual tasks, although the rate of deterioration depends on the task; t his too can be limited by cell transplantation. Current results indica te an optimistic future for transplantation in human retinal degenerat ive disease, but also emphasize the many preparatory steps that still have to be made for a successful clinical outcome.