Gordon Brown was questioned by NBC host Brian Williams
Gordon Brown has been forced to deny suggestions he is slowly going blind.
The prime minister lost the sight in his left eye as a child, but he was asked in an interview on US television if his other eye was now also failing.
Mr Brown, who is in New York for a United Nations summit, insisted: "My sight is not at all deteriorating."
On Wednesday, the PM dismissed a suggestion by former home secretary Charles Clarke that he may stand down as Labour leader citing poor health.
Mr Clarke raised doubts about Mr Brown's wellbeing in an interview with the Evening Standard newspaper, saying the prime minister's "own dignity" could prompt him to use it as a reason to resign before the next election.
But asked about the remarks, Mr Brown told BBC Radio 5 live he had no health problems.
"I'm healthy and very fit. I run a lot to keep fit," he said. "I keep going and I've got a job to do."
Mr Brown was speaking to NBC Nightly News on Wednesday when he was asked by anchor Brian Williams about reports that he needed documents to be printed in large text.
He replied: "I lost the sight in one of my eyes playing sports - I was playing rugby when I was very young.
"I had all sorts of operations. I then had one operation on the other eye and that was very successful, so my sight is not at all deteriorating."