Octopuses have hundreds of suckers, each one equipped with its own ganglion with thousands of neurons.

WSJ: The Brains of the Animal Kingdom

The artificial retina is composed by neuronal photoreceptors, called cones and rods, which capture light signals and transform them in electrical signals, transferring them to the retinal ganglion cells and, through the optic nerve, to the brain.

FORBES: Artificial Retina From A Photovoltaic Polymer

Radcliffe had been suffering from a ganglion, a swelling that forms around the tendons or joints, on the same foot and it is believed that it may have put pressure on the toe by changing her foot dynamics.

BBC: Radcliffe out of London Marathon