Striking out on your own to hike the trails of America's backcountry, with just your dog for company, would be a dream for many. But what if you can't see the trail, and your dog is key to your survival?
Trevor Thomas, 46, had his life abruptly interrupted when he lost his sight 10 years ago through a rare eye condition. He was looking to move away from his career in corporate sales and had just completed a law degree. A self-professed "adrenaline junky", he loved racing his Porsches and downhill mountain bikes. Now, as a blind man, he pits himself against nature, which he says, is the greatest opponent of all.
When he was in his mid-30s, he was told he would lose his sight. What he wasn't told was how long it would take. He didn't try to imprint visions of beautiful sunsets on his mind's eye to carry with him throughout the rest of his life, rather he focused on remembering the faces of his loved ones and what it was like to look in to their eyes.
"It was like living in a terrible limbo," he says. "In the end, I was praying for my sight to go, so I could start my life again."
It took eight months for his sight to go completely.
Thomas worked hard to pick up the threads of his life, beginning with the difficult task of learning to read Braille.
There is often less sensitivity in adult fingers to feel the dots that make up the Braille code, and most struggle to learn it - but he mastered it well enough to read a novel slowly, and the labels on tins and packets in his kitchen.
He soon began to worry about what he could now do for a living. He felt he hadn't honed the practical skills need to hold down a job in the law as he had planned.
Thomas became depressed and very angry about the loss of his sight, his former life and, as he saw it then, his independence. A friend suggested hiking might help him out of the rut in which he found himself. He had learnt to use a white cane for walking safely through suburban streets but when he wanted to learn skills that would be useful for hiking off-road, his rehabilitation worker advised against it.
Despite this, Thomas started doing short hikes on the trails of his home state of North Carolina on his own.
"Hiking alone seemed to give me some control," he says, "and having to teach myself, though frustrating at times gave me the self reliance that I so desperately needed.
"I was able to take ownership of my successes and learn from my failures. I hated the way society viewed me as a blind person and could not accept the lessened expectations that were placed on me, so I decided early on, that however I was expected to exist as a blind person, I was going to be different.
"Had I waited for my anger to subside, I feel that things would be dramatically different for me. I fear that I would be yet another blind person, who society had convinced that blindness is a life-ending condition and any hopes and dreams I had left would have been quashed."
One day, while shopping in a camping store for a sturdier alternative to a white cane for forging through rough country, Thomas met a teenager who had just completed the Appalachian Trail. The AT, as it is known, stretches some 2,180 miles (3508 km) through the Appalachian mountains on the eastern edge of North America. Beginning in Georgia in the south and ending in Maine in the north, it takes in 14 states along the way.
The teenager was brimful of his adventures - how he'd nearly frozen to death, had got up close to a bear - and had a deep sense of achievement for getting through and finishing. Thomas left the store with some trekking poles and the resolve to conquer the AT himself, and to do it solo.
He quickly, however, discovered that there were no resources available for a blind person. There were no tactile maps he might interpret with his fingers, no guides in Braille or in audio form at that time. He also knew that GPS was not accurate enough for a blind person to be able to pinpoint exactly where they were.
Thomas sat down with the same young adventurer he'd met at the camping store, and together they painstakingly mapped the trail. Thomas was given simple instructions of the route he would take on a daily basis. These were then entered into his smartphone, which read the information back out to him when he needed it.
It took 18 months to train and prepare for the trek, and in 2006, he set off. He wasn't too worried about the possibility of being alone for long periods of time.
"I knew that if I found myself in real trouble, all I had to do was sit by the trail and wait. Eventually someone would come along," he says.
Up to three million people visit the trail each year, with about 2,000 attempting to "thru-hike" from end to end. Only one in four succeed.
Hikers on the AT often take a "trail name", which describes their characteristics or experience. For Thomas, unsurprisingly, it was 0/0 - a reference to his level of eyesight.
He completed his trail in six months and two days.
But it wasn't to end there. For the next five years or so, Thomas continued to hike different trails. By 2011, he had hiked 12,000 miles, some partnered with a sighted person and some solo. However in that year he suffered a setback when he failed to complete the Colorado Trail.
"I was supposed to hike with a partner, who did not show up," he says. "I went as far as I could, alone, but knew I would not be able to finish because I had not prepared to go alone.
"It was that experience that led me to change everything about the way I hike, including applying for and getting my guide dog Tennille, so I would be able to hike the more technical and less travelled long trails without having to rely on a partner."
In September 2012 Thomas and Tennille graduated from the Guide Dogs for the Blind. She is the first guide dog specially trained for long-distance hiking. She applies some of the same principles of finding the path of least resistance in urban areas to the back country. She wears a small backpack to which Thomas attaches a lead through which he feels her movements. She walks ahead of Thomas and he walks in her paw-prints.
She uses her training and her own sense of self-preservation to stop Thomas going too close to danger.
Guide dogs in cities and towns
- In towns and cities guide dogs are trained to find a straight line of travel for their owners.
- They avoid obstacles and traffic, navigate crowds and are usually good at finding staircases and doorways.
- A handler follows the dog's body movements through a lightweight handle lying along its back. which is clipped to a harness.
More from Ouch: Assistance dogs: How to spot them
"For things such as blowdowns, large rocks and other impediments that could trip me, she will stop and hop up on them or put her front paws on them," he says. "Anything serious will cause her to stop dead in her tracks and, if necessary pull, me away from the threat. Once we come across something that has to be dealt with, it is up to me to figure out how to deal with it."
He taught the black Labrador-retriever to fear rattlesnakes by showing her a fake one and giving her a fright. Thomas is constantly talking to his dog to encourage and praise her, and he believes this also keeps dangerous wildlife at bay.
Every morning on the trail Thomas listens through and memorises that day's written map. He then keeps track of how far he walks and when he thinks he and Tennille are approaching an intersection as noted on his reference, he asks her to find it.
Tennille is also trained to find signs nailed to trees or posts that provide hikers with useful information, like the number of miles to a campsite. Thomas then reads these letter by letter, with his fingers. He says they haven't always stayed on the same trail they set out on, but they have never been totally lost either. The only explanation Thomas can think of for this is that Tennille is able to pick up the scent of other hikers who have gone before them.
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Trevor Thomas spoke to Outlook on the BBC World Service
Listen to the interview again
Looking after his dog's welfare, Thomas says, is his top priority. Boots protect her paws in extreme terrain and conditions and she has her own airbed and sleeping bag. A sprained hamstring is her only injury.
In 2009, when it became clear to Thomas that this extreme form of hiking was going to be, in a sense, his life's work, he set up a charity to encourage young blind people to pit themselves against the elements. His charity the FarSight Foundation has also provided him with a small army of volunteers who meet Thomas every five days or so when he is trekking to resupply him with food.
Some people have accused Thomas of trying to hike away from his disability. But he rejects this, saying that if he were given the choice of being able to see again now, he wouldn't take it. That, he says, would feel like running away from his problems.
"Being alone in the backcountry is terrifying at times and to this day, still can be, but it is also invigorating," he says "It is the one environment which does not discriminate. It treats me the same as everyone else. It will, also, not take pity on me because I am blind."
He claims that reaching the end of a trek or summiting a mountain means more to him than it does to people who can see.
"When I reach the end of a trail I remember how it feels. I feel the stones under my feet. I remember the smells, the sounds and the effort I made to get there - those are the things that remain with me, they'll just remember the view".
Trevor Thomas spoke to Outlook on the BBC World Service. Listen again here.