Runner Paul Jenkins is hoping to run his 100th marathon, but Sunday's race in London will be his first attempt at running the distance blind.
Paul Jenkins is hoping to complete his 100th marathon
The 48-year-old from Cardiff ran his first marathon in 1981 and has completed 99 of the 26-mile runs in countries across the world.
But since losing his sight in 1989, Paul has not attempted the distance.
He hopes to achieve his ambition of completing 100 marathons at the London event on Sunday.
"I am looking forward to it with some anticipation," he said.
"I haven't set myself any time targets - I'm just going to run it and hope I can complete it."
Paul is taking part in the marathon with his running partner Josh Kingston and together they have put in around 14 hours a week training since December.
Paul added: "It is very different running when you can see because it is such an individual sport - you can stop and start as you please and go training when you like.
"But when you are blind there are all sorts of other things to consider - things that you take for granted when you can see."
Paul lost his sight 16 years ago due to a condition called Leber's Optic atrophy, which means that optic nerves stop working leading to partial or complete sight loss.
Before his blindness, he had run in 99 marathons and had taken part in 30 ultra distance runs (between 30 and 1,000 miles).
He has taken part in runs since losing his sight but has not taken up the challenge of a marathon until now.
"It is something I have been putting off and off and off for a long time," he said.
"Then a friend said he was going to do the Cardiff marathon and I thought about doing it.
"But having run marathons before, I knew that the London marathon would have big crowds to support the runners.
"So decided that for my 100th marathon I would do the London marathon.
"I just hope I can do it," he added.
Paul has chosen to raise money for Guide Dogs For the Blind as part of his marathon efforts.
"I have had a guide dog called Ozzy for about six years now and he has made such a difference to my life," he said.
"He has even helped me with my training because getting to the gym with Ozzy takes me about half an hour - if I was trying to get there with just my white cane it would take twice as long," he said.