He was born with Congenital Toxoplasmosis which took most of his eyesight from the age of eight, but he sees himself as one of the lucky ones.

Prior to that, he had low vision which enabled him to still see colour before the condition returned and "took the rest of" it.

But it's not going to stop him competing for the second time at next month's event in Sydney.

"I grew up with kids who were born blind, so I look at it as I got to see colour, I got to see people and everything else - all things they never got to see," Mahr said.

"So at least if someone says to me 'this is green' or 'that's blue' I still know the basic colour, but for people who have never had sight ... how do you describe that to them?

"How do they even know what that is?"

He completed last year's event in a more than respectable time of one hour and 47 minutes.

With a training regime that includes gym sessions four times a week and competing in the Port Macquarie parkrun every week, he believes he can improve on that on August 11.

Mahr admits he enjoys a challenge and while most see him as an inspiration he believes he's just finding different ways to do things.

"I know people see me as an inspiration, but I feel like I'm just getting out there and joining in with everybody else and doing what other people do," he said.

"I'm just finding a different way to make it work. Where there's a will, there's a way."

The 32-year-old has already overcome his share of challenges - it would be brave to back against him improving on that one hour, 47 minute time from 2018.

"Fitness for me is a big thing," he said.

"I was quite overweight for a while so in the last three years I've got really into my fitness and entering into City2Surf was one of the goals that I never thought I'd do."

While his four-legged friend Yoric has pounded the pavement alongside him for years, he will be replaced by a guide for the 14-kilometre test from Hyde Park to Bondi Beach.

"There is always someone running with me and we have a bit of rope between us," Mahr said.

"It's a bit like a guide dog really because they always have the harness and are always on the left hand side, so the guide is on the left-hand side.

"I'm so used to feeling the movement of their body or them giving me a gentle shove to the other direction without verbally telling me we need to dodge someone we do it automatically."

Mahr is also looking to raise $3000 for the Guide Dogs Australia after raising more than $2300 last year.

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