Gordon Brown made clear yesterday he would continue as Prime Minister despite being told his eyesight could be affected by a new medical condition. Mr Brown, who is blind in his left eye after a teenage rugby injury, attended Moorfields Eye Hospital in central London on Friday after tests last month revealed he has two minor rips on the retina – light-sensitive tissue – of his right eye.

He was told about the rips after an annual check-up in his good eye. Experts yesterday said such tears can lead to a detached retina if not caught early enough and treated. Downing Street and doctors insisted there was "no deterioration" in his eyesight as a result of the tears.

Yet the development will fuel speculation that Mr Brown could be preparing the ground for an exit strategy from Downing Street after failing to turn around the polls, despite surviving the conference season without any major setbacks. However, a new opinion poll shows the Tories, on 45 per cent, have stretched their lead to 19 points. The ICM survey for the News of the World also suggested that voters preferred the Tories in almost every policy area, from law and order to schools, Afghanistan and tax.

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It was also "highly likely" that Mr Brown would be asked to repay some of his expense claims, the BBC reported. The Prime Minister is among hundreds of MPs who may receive a letter this week from Sir Thomas Legg, the auditor investigating parliamentary allowances, requesting either further details or repayment.

Mr Brown's only noticably contentious expenses claim was that for cleaning services which involved him paying his brother Andrew £6,577.

News of Mr Brown's health problem would have brought fresh anguish for the Prime Minister, who in his conference speech last year spoke movingly of how NHS doctors fought to save the sight in his good eye after the rugby injury that resulted in a detached retina.

However, the disclosure raised questions over whether he had been completely open with the general public when being questioned about his health on BBC's Andrew Marr programme last month. Downing Street refused to deny the suggestion that the retinal tears were discovered by tests before the television interview took place on 27 September.

On the programme, Mr Brown told Marr: "Every year I have to check, as I did only a few days ago, that my eyesight is good. There has been absolutely no deterioration."

His words, with hindsight, appeared carefully chosen, because by then he would have started monthly check-ups as a result of the condition.

No 10 said yesterday: "This summer, Mr Brown had his annual eye check- up which was fine. Later, he had his retina checked. After examinations, surgeons found that the retina had two minor tears. However, as there has been no further deterioration and no change in his eyesight, they decided against further operations. Mr Brown visited Moorfields eye hospital yesterday as part of regular checks on his eyes, and this check was also fine.

"Were there to be any change, he would of course make a further statement." No 10 said yesterday that the Prime Minister had been "entirely consistent" because there had been no deterioration in his sight. Asked whether it would affect his ability to continue with the job, a Downing Street spokesman said: "Absolutely not."

In a book by the Sky News political editor, Adam Boulton, it was claimed that Tony Blair believes Mr Brown may find an excuse to "duck out" of the election, possibly using health grounds as an excuse.

Tears to the retina can develop with no obvious symptoms, but, often, sufferers will experience either flashes of light or floaters – black spots or lines in the field of vision caused by bleeding of torn retinal vessels or the formation of small clumps of vitreous matter. Left untreated, tears can lead to retinal detachment. The part of the retina which becomes detached will not function properly, resulting in vision loss or even total blindness.

Dr Winifred Amoaku, the vice-president of the Royal College of Ophthalmologists, said laser treatment was recommended in such cases.

MPs return to Westminster tomorrow amid renewed manoeuvres to oust Mr Brown, including the possibility of rebels fielding a "Brown must go" candidate for the election of chairman of the parliamentary party. But Mr Brown can find comfort in the news that Sir Thomas Legg, who is investigating MPs' expenses, could stymie a revolt. It is understood that Sir Thomas is to send an auditor's letter to half of all MPs , ordering them to repay money or provide further details of their parliamentary allowances.