When Michael Robertson was in his 20s, his bike collided with a car. The crash left his helmet in six pieces and his confidence so shaken that, despite a deep connection to his bicycle and the freedom it afforded him, he quit riding entirely. The cause of the crash is fuzzy in his recollection, in part because he was going blind.

Two decades later, and with profoundly worse vision, Robertson is preparing to fulfill a lifelong dream by cycling across the country.

On June 25, he and his friend Hans Breaux will fly to the West Coast with bikes in tow. Their journey will take them from the westernmost point in the continental U.S. to the easternmost — Ozette, Washington, to West Quoddy Head in Lubec, Maine — following the Canadian border. The trip of roughly 4,000 miles will take them between seven and eight weeks.

During the entirety of the trip, the front wheel of Robertson's bike will rarely be more than two feet from the rear wheel of Breaux's.

Robertson suffers from cone-rod dystrophy, a hereditary degenerative condition that affects the light receptors in the back of the eye. His visual acuity is 20/1000, or five times the threshold for legal blindness. An object 20 feet in front of him is as clear as the same object seen at a distance of almost a quarter-mile by someone with perfect vision.

Because cone-rod dystrophy does not affect the lens of the eye, glasses don't help. Robertson's eyes are highly sensitive to light — another effect of the condition. He wears sunglasses indoors and carries several spares, including a sunny-day pair he jokingly compared to welding goggles.

His vision is getting worse, but he can still read with a magnifying loupe. Facial recognition is out of the question. Even at close range, he said, people appear as forms without features. He picks up on gait and other cues to identify friends and acquaintances.

His vision was closer to 20/700 three years ago when he decided to get back on his bike. Inspired by the Race Across America and Daniel Kish, a blind man who taught himself echolocation that eventually allowed him to ride a bike without sight, Robertson signed up to ride in the Trek Across Maine.

Robertson rode with a small group that included Breaux. "They just kind of guide-dogged me across the state," he said. "I started thinking, 'What if somebody wanted to climb Katahdin?'"

Last year, Robertson and Breaux completed their third Trek. After the race, they started Shared Vision Quest to encourage the kind of partnership that had allowed Robertson to ride his bike 180 miles across Maine.

Finding clear-sighted helpers willing to "be the Hans for someone else" proved relatively easy, Robertson said. But when he approached organizations and agencies that work with the visually impaired and presumably could spread the word quickly, he hit a wall. They were more interested in limiting risks than offering adventure. As he described it, no one wanted to help a blind child climb a tree.

"They're blown away by what I'm doing," he said. "But it's almost like they don't want to tell my story."

Robertson and Breaux will be telling their stories during the cross-country trip, giving presentations about Shared Vision Quest and trying to raise awareness of the possibilities for people with visual impairments, especially if they have someone to help them.

They have a GoFundMe campaign for travel expenses and plan to raise additional money during the trip for retinal disease research at Massachusetts Eye and Ear.

Robertson acknowledged that a cross-country trip is a big step up from the Trek Across Maine — the planned route crosses 12 states, most of them bigger than Maine — but he's motivated by the challenge, or as he imagines it, the hundreds of tiny challenges that will make up his dream trip.

More importantly, there was no guarantee his vision would last long enough to do a shorter ride first.

Robertson and Breaux are planning to be entirely self-sufficient on the trip, camping along the route. There will be no support vehicle. In a short video about the trip, Breaux likened it to a backpacking expedition on wheels.

Bath Cycle & Ski is building Robertson a custom bike, though the special features are mostly those that any rider would want — custom sizing, light-as-a-feather frame — rather than adaptations for a visually impaired rider. One exception that got kicked around was a wireless sensor on Breaux's brakes that would buzz Robertson's helmet as a warning to slow down.

With his limited ability to see the sights, Robertson is focusing on other parts of the trip. Keeping his attention on the wheel ahead of him means always being a little on edge, but it's also meditative, he said, and there are plenty of other perks to "life at 15 miles per hour."

Mostly, he said, it's about meeting people from other parts of the country and taking in the unfamiliar sounds and smells along the way.

"I hear Washington state has an amazing, clean smell because it's almost rainforest," he said.