I do so love a medical mystery. From The Daily Telegraph:
Retired architect Mr Darby, from Leicestershire, had worn spectacles since the age of two but was stunned when he came round after surgery to clear the blood clot causing his stroke, that he could see clearly without his glasses.
...
Malcolm suffered a major stroke on May 13 last year when he was working in his office at home in Oakham and managed to tell his wife Sylvia, 68, to dial 999 before he collapsed.
He was rushed to Kettering General Hospital for surgery where a two-hour operation was carried out to remove a blood clot that was blocking 80 per cent of his right carotid artery in his neck.
...
It is unclear why the stroke or the operation appears to have caused such a dramatic improvement in Mr Darby's sight but doctors believe there may have been pressure on the optic nerve at the back of the eye which was relieved as the clot was cleared