sâmbătă, 1 septembrie 2012

The Science Behind The Chip That Could Restore Sight To The Blind

A microchip implant placed under the retina could revolutionize the lives of hundreds of thousands of people who have lost their ability to see.

The chip, developed by German-based company Retina Implant AG, is still in clinical trial but has already shown promising results for patients suffering from retinitis pigmentosa, a genetic disease that leads to blindness with approximately 1.5 million people affected worldwide.

Here's how it works:

The retina is a tissue in the back part of the eye that contains cells called photoreceptors. The photoreceptors convert light rays into nerve signals, which are then processed by nerve cells in the inner retina, sent to the brain and translated as images. The two types of photoreceptor cells are known as rods (responsible for peripheral and night vision) and cones (responsible for color perception). A normal-sighted person has about 120 million rods and about 6 million cones.

In patients with retinitis pigmentosa, the rods and cones die. As a result, the retina's inner cells and the optic nerve fibers that normally send impulses to the brain stop receiving information.

The retinal implant works by replacing the photoreceptor cells that have been destroyed.

There are currently two main approaches to retinal implants: subretinal and epiretinal.

In the epiretinal approach, a wireless implant is surgically implanted on top of the retina. A miniature video camera attached to the patient's eyeglasses captures light and transmits this wirelessly to the implant. This stimulates the retina's functioning inner nerve cells that send electrical impulses to the brain. The downside of this approach is that it requires several different parts, including a battery pack worn on the patient's belt to power the whole system.

The subretinal implant developed by Zrenner and his colleagues, on the other hand, is placed under the retina in a center spot called the macula. According to Retina Implant AG’s website, "the macular region is believed to be the ideal location because this is where light-sensitive photoreceptor cells are located which are responsible for producing clear images in normal-sighted people." The chip also moves with the eye, which means you don't have to move your head to recognize objects as with the epiretinal implant. It also leverages more electrodes than the epiretinal implants (1,500 vs. 64), which makes light and dark images appear more vibrant.

The subretinal implant chip's 1,500 light sensors are triggered by natural light. Electrical impulses stimulate the retina's inner neurons and signals are sent to the brain to produce sight.

The chip is powered by a small battery box in the pocket which forwards power and control signals for brightness and contrast adjustment via a wireless unit behind the ear to the implant by a sub-dermal coil and cable that runs to the eye.