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How to rewire the eye

Transforming nerve cells into light-sensing cells aims to restore sight in some blind patients

2:10pm, May 15, 2015

SEEING THE LIGHT  The brain’s window on the visual world is a multilayered tissue at the back of the eye called the retina. Light-detecting rods and cones sit at the very back of the tissue. They pass information to the brain via bipolar cells and ganglion cells. Humans and some animals have sharp vision thanks to the fovea, a window in the retina that offers direct access to the cones.

A man who had been blind for 50 years allowed scientists to insert a tiny electrical probe into his eye.

The man’s eyesight had been destroyed and the photoreceptors, or light-gathering cells, at the back of his eye no longer worked. Those cells, known as rods and cones, are the basis of human vision. Without them, the world becomes gray and formless, though not completely black. The probe aimed for a different set of cells in the retina, the ganglion cells, which, along with the nearby bipolar cells, ferry visual information from the rods and cones to the brain.

No one knew whether those information-relaying cells still functioned when the rods and cones were out of service. As the scientists sent pulses of electricity to the ganglion cells, the man described seeing a small, faint candle flickering in the distance. That dim beacon was a sign that the ganglion cells could still send messages to the brain for translation into images.

That 1990s experiment and

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