A soldier who was blinded by an explosion in Afghanistan will run in Sunday's London Marathon alongside an actor from Downton Abbey.
Lance Bombardier Rob Long, 24, said he would require "extreme concentration" to complete the 26.2-mile course.
He is part of a three-man team that includes Lachlan Nieboer who played a blinded soldier in the latest series of the hit ITV drama.
L/Bdr Long, from Greenwich, south-east London, said the only part of the route that he can "see" is what his feet can feel.
– Lance Bombardier Rob Long
Extreme concentration is the main thing. I can only see exactly what is underneath my feet.
It takes a lot of concentration to keep the rhythm and pace going. I've built up a lot of trust with my running partner.
The soldier, from 5th Regiment Royal Artillery, said he only began long-distance running in November but is hoping to finish the race in under four hours.
He was blinded in July 2010 when one of his unit accidentally triggered an improvised explosive device during a patrol in Sangin, southern Afghanistan.
He immediately lost his left eye, while his right eye was removed later as shrapnel had severed the optic nerve.
"I knew my career was over the second I woke up," L/Bdr Long said.
He described how he had to take his recovery "day by day" and said it was "really difficult" to come to terms with not being able to see.
Blind Veterans UK visited him in hospital and gave him the advice he needed to start walking again.
The charity has also helped him prepare for the arrival of his first son, as his wife is expected to give birth in two weeks.
L/Bdr Long said the organisation has given him "a real head-start" in knowing how to measure liquids for the baby's bottle and change nappies without his sight.
He is running in aid of the charity on Sunday as a way of promoting its work.
Actor Lachlan Nieboer decided to enter the race after researching for a part in episode two of the second series of Downton Abbey.
He played a soldier who had been blinded by mustard gas in the First World War and who went on to commit suicide.
– Actor Lachlan Nieboer
I found myself being more interested in what Blind Veterans UK did.
The 30-year-old from Brixton, south London said his meetings with the charity helped make the role "come alive".
He said soldiers react to losing their sight in a number of ways, from "lashing out", suffering depression or even wanting to take their own lives.
Nieboer, who has recently finished filming alongside Harry Potter star Rupert Grint in war film Into The White, said he was "chilled" about what time he will record in the race but hopes to finish alongside L/Bdr Long in under four hours.