A man who began losing his sight as a teenager and eventually went blind has been able to read letters and identify a clock face after being fitted with an experimental electronic chip in his eye.

Miikka Terho of Finland had the chip implanted behind the retina in his eye in Germany. Now in his 40s, he was one of a number patients to have the chip inserted, but he performed particularly well in subsequent tests.

Mr Terho went blind after developing the hereditary disease, retinitis pigmentosa (RP). It is characterised by degeneration of the photosensitive cells in the retina of the eye which perceive light and colour. These cells are called the rods and cones.

RP is a major cause of blindness in people under the age of 60 and affects millions of people worldwide.

In Mr Terho's case, he had enough peripheral vision to tell the difference between night and day. However he had had no central vision for over 10 years. Central vision is essential for everyday things, such as recognising people, reading and driving.

According to lead researcher, Prof Eberhart Zrenner of Germany's University of Tuebingen, some of the participants who had the chip implanted noticed no improvement with their vision because their condition was already too advanced to benefit from it, however most were able to pick out bright objects.

The researchers then discovered that the best results were achieved when the chip was placed further behind the retina - in the central macular area - of three people, including Mr Terho.

After the chip was inserted into Mr Terho, he was able to recognise a clock face, as well as cutlery and a mug on a table.

He was also able to move independently around a room and approach people who were present.

Then, in further tests, he was able to read large letters that had been placed in front of him. In one test, his name was placed before him, but was deliberately misspelled as Mika, instead of Miikka. He was able to pick out the mistake.

Prof Zrenner and his team worked with the private company, Retina Implant AG. Details of their work are published in the journal, Proceedings of the Royal Society B.

Commenting on the breakthrough, Avril Daly, chief executive of Irish charity, Fighting Blindness, said Prof Zrenner should be congratulated for his ‘tireless work' in the area of retinal research.

However she emphasised that the chip is at a 'very early stage' in its development.

"It's important that we recognise that clinical trials can take a number of years and so it could be some time before this product becomes generally available. We will be monitoring developments with great interest," she said.

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