Tests on a device that could restore sight to patients suffering from a common cause of blindness have produced "encouraging" results.

A prosthetic retina designed to combat the impact of age-related macular degeneration (AMD) is being developed by researchers at the University of Strathclyde and Stanford University in California, in the United States.

The condition affects the macular, a tiny part of the retina at the back of the eye, and damages a layer of light-sensitive photoreceptor cells that help the person see.

One in every eight people aged over 85 have AMD, while one in 500 people aged 55-64 also have it.

The device electrically stimulates the neurons in the retina left relatively unscathed by the effects of AMD, while an infrared beam is projected through the eye and transmits information. It doesn't require any wires and is easy to implant, scientists said.

Initial lab tests have been "encouraging", according to research published in the journal Nature Photonics.

Dr Keith Mathieson, from Strathclyde University and a lead researcher on the project, said: "AMD is a huge medical challenge and, with an ageing population, is continuing to grow. This means that innovative, practical solutions are essential if sight is to be restored to people around the world with the condition.

"The prosthetic retina we are developing has been partly inspired by cochlear implants for the ear but with a camera instead of a microphone and where many cochlear implants have a few channels, we are designing the retina to deal with millions of light-sensitive nerve cells and sensory outputs.

"The implant is thin and wireless and so is easier to implant. Since it receives information on the visual scene through an infrared beam projected through the eye, the device can take advantage of natural eye movements that play a crucial role in visual processing."

The research was co-authored by Dr Jim Loudin of Stanford University and led by Professor Daniel Palanker, also of Stanford, and Professor Alexander Sher, of the University of California in Santa Cruz.

Professor Palanker said: "The current implants are very bulky and the surgery to place the intra-ocular wiring for receiving, processing and power is difficult. With our device, the surgeon needs only to create a small pocket beneath the retina and then slip the photovoltaic cells inside it."