Diffusion tensor imaging in acquired blind humans

Retinal implants as a future possible therapy of blindness rely on an intact neural transmission from the retina to the primary visual cortex. By now it remains unknown, in how far the absence of afferent input in blindness affects also the organization of the optic radiation. Using diffusion tensor imaging (DTI), the non-invasive evaluation of large fiber tracts including the optic radiation has become possible. This method is sensitive to changes of the axonal state such as wallerian degeneration. We have compared DTI data from 6 acquired blind patients with those of a group of 11 healthy control subjects. Neither the relative anisotropy quotient of the visual fiber tract and the pyramidal tract showed a statistically significant difference between the blind patients and the control group nor did the absolute values of the relative anisotropy in the pyramidal tract and the visual fiber tract. There was no axonal degeneration of the optic radiation in late onset acquired blindness. With the optic pathways remaining intact, transmitting electric signals of retinal implants to the visual regions of the human brain seems to be possible even after decades of acquired blindness.