Johnston lost his eyesight due to a degenerative disease of the retina at just 14 years of age and has just 10 per cent vision.

Currently 27 and living in Helensburgh, just south of Sydney, Johnston will run alongside his pilot Glenn Gorick for the gruelling event.

His story is inspirational, having not started sports until after he lost his vision.

He was diagnosed as a 14-year-old and by the time he was 17, his eye sight was all but gone.

He converted to Braille to complete his High School Certificate and will this weekend be the first visually impaired athlete to do the Ironman since Ched Towns in Forster almost 15 years ago.

“He’s aiming for the Rio Paralympics,” Gorick said. “He needed to get out of the house and that’s why he turned to running and ocean swimming.”

Gorick will run, swim and ride with Johnston during the Ironman to ensure his safety and help him along the way.

“It’s truly inspirational,” he said. “He’s even encouraging the able-bodied athletes to do it.

“I’ll be his eyes for the entire race and will be beside him the whole time.”

Johnston is also raising money for motor neurone disease and is excited ahead of his first race in Port Macquarie.

“I only got into sport about seven years ago,” he said. “It’s a lot of fun and gets my mind off everything that’s going on.”

Johnston has completed a triathlon before, racing alongside Tony Abbott last year.

He is not expecting much for his first Ironman in Port Macquarie, but he would like to say he crossed the line when it’s all said and done.

“As for the race on the weekend, I just want to get over the line and finish,” he said.  “If I do that, I’ll be happy.”