Progress in retinal sheet transplantation.

The aim of retinal transplantation is to prevent blindness and to restore eyesight, i.e. to rescue photoreceptors or to replace damaged photoreceptors with the hope of re-establishing neural circuitry. A promising experimental paradigm is the sub-retinal transplantation of sheets of fetal retina, with or without its attached retinal pigment epithelium (RPE), into recipient rats with retinal degeneration. Sheets of fetal retina have already developed their primordial circuitry. Such transplants can develop lamination resembling a normal retina dependent on the presence of healthy RPE either from the host or from the graft. In several retinal degeneration models, transplants have been shown to restore visually evoked responses in an area of the superior colliculus corresponding to the placement of the transplant in the retina. The functional effect of transplants may be due to transplant/host connectivity and/or rescue of host photoreceptors. 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 rats with retinal degeneration.