Rapid enhancement of transplant-mediated pupilloconstriction after elimination of competing host optic input.

Retinae transplanted over the brainstem, when directly illuminated, cause pupilloconstriction in the host eye. This occurs even when the host eye is maintained in darkness. If the host optic nerve is then severed, the transplant-mediated response is substantially augmented within 1-2 days. It is suggested that this is due to enhancement of the signal-to-noise ratio resulting from elimination of dark discharge in the host optic nerve.