A scientist who has been credited with saving the sight of at least 200m people worldwide since pioneering cataract surgery has been knighted by the Queen.

Sir Harold Ridley, 93, developed the sight-saving operation 50 years ago.

He used an artificial lens made of Perspex to replace those in eyes which became clouded by cataracts.

He faced initial opposition from the rest of the medical profession but Mr Ridley persisted in seeking a manufacturer to market the artificial lenses.

It now takes just 20 minutes to perform a cataract operation, with five million people having their sight restored every year through the technique.

An artificial replacement is implanted into the lens of the eye which has been damaged by the cataract.

Among those whose sight has been saved by Sir Harold's work are the Queen Mother and former South African president Nelson Mandela.

At his investiture at Buckingham Palace, Sir Harold said the thought of tampering with people's eyes had, at first, frightened the medical profession.

"I think the medical profession were scared stiff that it would cause problems with a very delicate organ, the eye," he said. "I couldn't afford to make a single mistake because the whole world was watching me."

The condition is the most common cause of blindness in people over 50 in the UK.

Sir Harold said he was delighted the operation had eventually been recognised as one which can dramatically improve people's quality of life in old age.

"It's a great advance in science - I feel gratified, not clever," he said.

Sir Harold had his own eyes treated a decade ago.

"I am the only man to have invented his own operation," he said.