He had already lost his left eye in his teenage years, and suffered a loss of vision in his right eye, despite four major operations.
In September, 2009, came a moment in Downing Street when he wondered if he might lose his sight altogether.
He woke one morning in 2009 with foggy vision, and knew something was very wrong.
In an extract from his memoirs, My Life, Our Times – to be published next week - he reflected on the worrying time.
After carrying out an engagement, he went straight to a prominent eye surgeon who said his retina was torn in two places and he needed immediate surgery.
For a week he attended to his Cabinet business, speech-writing and attending meetings without being able to see properly. He didn’t tell colleagues what was wrong.
Mr brown turned to a friend, retired surgeon Hector Chawla who travelled from France to inspect his eye and decided surgery was not necessary unless it deteriorated further.
“I am grateful that the retina has held to this day and I feel lucky beyond words,’’ said Mr Brown.
“Nonetheless, it was after losing the sight in my left eye and then some of the sight in my right one that I started to think more about my future.
‘’There were certain things I couldn’t or shouldn’t do – playing the sports I loved, and driving a car, despite having a licence – but I was not going to be deterred.
“Even if I felt fate had dealt me a hand I would not have chosen, my time in and out of hospital – and the fight for my eyesight – gave me a perspective that I still feel helps me to be more understanding of difficulties facing others in a far worse position than me.”
> Gordon Brown - My Life, Our Times will be published by The Bodley Head on Tuesday November 7.