Retinal transplantation--advantages of intact fetal sheets.

Retinal transplantation aims to prevent blindness and to restore eyesight, i.e., to rescue photoreceptors or to replace damaged photoreceptors with the hope of reestablishing neural circuitry. Retinal donor tissue has been transplanted as dissociated cells or intact sheets. A promising experimental paradigm is the subretinal transplantation of sheets of fetal retina with or without its attached retinal pigment epithelium (RPE) into recipient rats with retinal degeneration. As long as healthy RPE either from the host or from the graft is present, such transplants can develop lamination resembling a normal retina. Different methods have been used to demonstrate transplant/host connectivity. In two different rat retinal degeneration models, visually evoked responses can be demonstrated in an area of the superior colliculus corresponding to the placement of the transplant in the retina. In summary, sheets of fetal retina can morphologically repair an area of a degenerated retina, and there is evidence to suggest that transplants form synaptic connections with the host and restore visual responses in blind rats.