Even as a disease steadily deteriorates his vision, a lifelong motorcycle enthusiast makes a perilous journey through South America and its notorious Road of Death.

The wind is unrelenting. We leave Chile and ride 500 yards to a Bolivian customs and immigration outpost. For eight hours we sit in a tiny building watching sand blow under the door. The power is out, and the Bolivian customs officials will not release our bikes. We get approval just as the sun goes down. We have to ride 150 miles in the dark, in the freezing cold, without our support vehicle.

With my eyesight, riding at night is an act of faith. I tuck my bike behind Andres and Rob, the most experienced off-road riders in the group, and go chameleon. I will do what they do, an act of trust unprecedented in my life.

I read their taillights for direction changes, hills, drop-offs, use the path of their headlights to illuminate enough road to match their speed. I stand on the pegs to lower the bike’s center of gravity, making it less squirrelly on the gravel, potholes, sand and ruts. The road deteriorates into what locals call ripa—miles of washboard bumps. The bike chatters like a white ball on a spinning roulette wheel. I try not to dwell on the rest of the metaphor. If I drop into a rut or pothole, my number will be up. My heart beats a mantra. Not me. Not yet.

I ride almost entirely by feel, letting the bike handle the details—its suspension is quicker than my quads. I commit to the throttle, to the physics of a gyroscope (stability provided by spinning wheels that disappears if you slow). I don’t touch the brakes. I force myself to breathe regularly. Adrenaline turns my mouth to cotton. Evidently my body knows it’s in a fight-or-flight situation. I suck on a plastic tube that runs to a bladder of water built into my riding suit. Nothing. The tube is frozen solid, as are the water bottles strapped to my fanny pack. The container of antifreeze in our guide’s top box freezes, explodes and leaks antifreeze icicles. The cold poses more of a problem than the dark.

At minus 10 degrees centigrade, if a bike breaks down, it will be a matter of moments before hypothermia escalates the mechanical to the mortal.

Hours into the night I crest a hill to find the wind has deposited six inches of sand between two embankments. The sand swallows our front wheels. Just like that, Andres is sideways. I follow, sideways. Rob sees what is happening, touches his brakes and goes down.

Almost in unison Andres and I ride out three whiplash turns, steering with our knees and foot pressure, like skiers in powder. We apply throttle to unweight the front wheel, and finally, as the sand gets shallower, we bring the bikes under control.

We flick on the hazard lights, put the bikes on their side stands and run up the hill. Rob is uninjured, but there are five riders behind us, stretched across the night.

I am halfway across South America, exactly where I want to be.…

In college I started a journal, and the first entry describes a motorcycle ride through the streets of Hartford, Connecticut, shifting through the gears, feeling the front wheel lift, seeing the slash of red as my taillight reflected off the chrome trim of parked cars. The motorcycle made me a writer. It is a machine for generating words, a tool for seeing. Kick an engine to life and I enter an altered state, one that turns highways into hymns, momentum into moments.

I ride a motorcycle to take my eyes places where I’ll see things I’ll never forget. Unfortunately, my eyes do not return the favor.

Chicago, 2003: I’m sitting in a darkened doctor’s office, staring at eye charts. In the space of a few months my eyesight has deteriorated dramatically. I tell the doctor I can no longer read headlines accurately.

“I don’t think I could pass the vision test for a driver’s license,” I tell him.

He laughs. “This is Chicago. Everyone has an uncle in the DMV.” Then he looks at the back of my eyes.

Blood vessels have done to the retina what tree roots do to sidewalks. The macula—the part of the eye responsible for fine focus, for details—is swollen, leaking fluid from tiny eruptions. If you project a slide onto a rumpled sheet, some parts will be in focus, some parts won’t. There will be gaps and blind spots. Weirdly, the mind takes the fractured information and tries to make sense of it.

Pick a word in the middle of this page. Focus on just that word. How well do you see the other words on the page? That’s how I see.

The retinologist launches a Star Wars battle on the inside of my eyes, cauterizing blood vessels with a laser. Two or three times a year he plunges a needle into one eye or another, injecting steroids to reduce swelling. It is not a cure, but it slows the deterioration.

I don’t talk about my eyes. If asked, I tell people I can still sit for hours at a computer, watching porn. At least I think it’s porn.

Someday soon I will be unable to ride. As a result, mileage is the only thing that matters. The road ahead. I start taking long rides, logging miles in South Africa, Canada, France, Spain, Central America, the American West.

Then one day my editor, a man possessed of a manic restlessness, contacted me: “I want a feature where you ride across Mongolia or Siberia or something like that Ewan McGregor TV special, Long Way Round. Something that really gets at the heart of what it’s like to ride and be out there in the elements, doing what every man dreams of. We’ll need frightening locals, harsh weather and loads of color—like across Afghanistan but not as dangerous.”

I contact Compass Expeditions, an Australian outfit that keeps a fleet of BMW motorcycles in South America. By stitching together three of their tours, I can go 5,000 miles from Rio to Lima, spending six weeks getting to know the planet. I’ll have a guide and a support vehicle filled with spare parts. I’ll traverse coast highways, jungles, deserts, high plains, the Andes. I’ll challenge El Camino de la Muerte—the Road of Death—in Bolivia.

At a hotel in Rio in September I meet two New Zealanders who, for reasons not unlike my own, have signed on for the coast-to-coast adventure. We share a passion: the desire to take a skill and use it to unlock the world. On the other side of six weeks we will be different people. Different, i.e., crazed or dead.

Rob, a musician–math instructor, reports he’d been in the country barely 10 minutes before facing drawn guns and someone demanding money. He seems unfazed.

John, a software engineer with a voice that registers on the Richter scale, asks Rob if his Leatherman has a file. He’s chipped a tooth and wants to grind it smooth.

One morning as I try to figure out a mounting system for my helmet cam, I tell them my editor’s hopes for this article. A hint of danger. Exotic locales. Getting buggered by commie guerrillas and capturing it in high-def. “For that,” asks John, “would you mount the camera facing backward?”

In Penedo, a town two hours from Rio de Janeiro, we pick up the BMW F650 GS motorcycles that will take us across this continent. I don’t tell anyone about my eyes.

Micho, our guide, warns us that South Americans are aggressive drivers. Oncoming cars may pull into your lane to pass and expect you to deal with it. Taking electrical tape, the Kiwis put yellow arrows pointing to the right on their windscreens, a reminder that here they have to drive in the opposite lane from home. On the windscreen of my bike I put an arrow of yellow tape pointing straight ahead.

We spend the first few days getting used to the bikes and the odd rhythms of Brazilian roads. We learn to dodge the unexpected: Dog. Goat. Rooster. Vulture. Speed bump. Town. On the coast highway near Bertioga, I have a ­startling vision. What I think is a bag of trash that has fallen out of a truck reveals itself to be a religious fanatic kneeling on the center line, eyes closed, arms outstretched and raised toward heaven. Rapture? Surrender?

In the coming weeks I will see gravel take flight as what I thought was stone becomes birds. I will see boulders heave themselves from the grass and become bulls. I will throw open a hotel room window and watch a tree dissolve into hummingbirds, then resolve into a tree.

That I can’t read road signs doesn’t bother me. None of us knows Portuguese. Faced with confusing signage for restrooms (ele and ela) Rob comes up with a mnemonic: Would you rather go into a restroom with Elle Macpherson or Ella Fitzgerald?

We stop at fruit stands to buy oranges. The vendors sell window stickers of Christ, Bob Marley, Che, the Playboy Rabbit Head, Yosemite Sam, Betty Boop. A truck driver from Alabama would feel right at home. The magazine racks sell the same glossy dreams, the cleavage and lip gloss, the tips to flatten your abs and improve your sex life. I begin to doubt local culture exists.

And then I take to the highway and catch out of the corner of my eye a hillside covered with horse trailers—a gaucho rodeo. Cowboys are chasing a fake cow being towed by a motorcycle, dropping a lariat over the horns, keeping alive the old skills.

After a week of coast highways, fishing villages and colonial towns, we turn inland toward the highlands of Brazil. A sign even I can read warns atenção: curva sinuosa. The BMW offers its own translation. Sinuous, sensuous curves. The road coils and uncoils beneath me. I create smooth arcs of acceleration that intoxicate. At 60 mph, the BMW scampers, showing off an agility that delights. The passing surge—from 60 to 80—leaves slower vehicles in the mirror. We ignore double lines, pass on corners, anywhere there is an opening—because we can. There is nothing quite as stirring as the sight of three bikes locked in formation, angled over, sweeping through a turn.

We will ride just shy of flat-out for entire days on roads so empty the only distraction will be three pigs crossing, a mule-drawn cart, a gaucho on horseback. To ride at speed is an act of sustained concentration. I extend my sense of sight to the breaking point, aware that a blind spot may contain an oncoming truck.

We pass vultures having their morning meal. A dozen birds perch on the corpse of a large goat to form a black, seething mass, like dog-size maggots with feathers.

Day 6, Brazil: The bodies lie under blue tarps. Leather boots indicate the two are male and, until recently, young. An emergency response team stands idly on the hillside near an ambulance. Three women wrapped in blankets sob hysterically. On the shoulder a Mercedes truck seems isolated and ashamed. The cab sports two impact craters just below the windshield, a good eight feet off the ground. Near the truck is a motorcycle, wadded into something the size of a medicine ball, and the crushed remains of a helmet.

Here lives ended.

Motorcycling is a subtle sport, one that harnesses enormous forces with the twist of a throttle, the gentle push on a handlebar, the squeeze of a brake lever. When you do it right, the bike becomes invisible and you are a creature of flight. Do it wrong, and those forces reveal themselves in mangled metal and mauled flesh. A moment’s inattention and the last thing I will see is the big blue tarp. I’ve accepted and been shaped by that risk for most of my life.

The cobblestone road becomes a dirt track winding through hills. We pass cascading rivers, a farm with a giant spinning water wheel, pastures filled with indifferent cows and small towns with churches letting out. I come around a blind corner at the same time a tanker truck enters from the other direction. If this were a graphic novel, the next frame would show the look of surprise and fear on the driver’s unshaven face. The beads of sudden sweat.

I hear the shriek of locked brakes, the sound of a couple of tons of metal scrabbling across the road into my lane. To my left: truck. To my right: a hundred-foot drop into a river. I aim for the space between and open the throttle.

My heart beats a mantra. Not me. Not yet.

I will hear the noise of those shrieking tires in my sleep for weeks.

Day 12, Argentina: New riders join the group. Newts shows up wearing a T-shirt from the Lazy Gecko, a bar in Cambodia, that depicts a line of marching penguins and the caption one by one the penguins took my sanity. It befits his shaved head and goatee. A former machine gunner with the Australian army, he’d served in Somalia and East Timor before he was diagnosed with post-traumatic stress disorder. The army shrinks told him to destress, so he took up world travel—visiting former war zones as a tourist. Over drinks he tells of waking up in a Kuwait hotel to find himself caught in a shoot-out between the army and Al Qaeda.

“If you call up the BBC footage, I’m the guy in the zip-tie handcuffs and a Hawaiian shirt, sitting on the curb behind an armored vehicle that’s pumping 50-caliber shells into the hotel,” Newts says.

I’m relieved to have him along. If anything is going to happen on this trip, it’s going to happen to Newts.

Andres, a Colombian financial advisor, raises the mischief quotient. His English has a tinge of Borat, the Sacha Baron Cohen character. One night he tries to teach us the music of the Spanish language. He starts by having us practice the proper way to greet a policeman. We repeat the phrase until we have it right. Hijo de puta. Hijo de puta.

The phrase, it turns out, means “son of a bitch.”

We pull into a roadside café with no name. A sweating, gap-toothed chef throws meat onto a sidewalk grill, the smoke collecting under the overhanging tin roof. Andres translates the menu: “cow parts.” The waitress brings a wooden plank with cow ribs, cow intestines, an udder and possibly a tongue.

John asks, “Does this qualify as a hint of danger?”

The tour dossier had said we would discover exotic cuisine like alligator and guinea pig. It made no mention of projectile vomiting inside a closed motorcycle helmet.

Day 18, Argentina: When we wake in Purmamarca—a town lined with hardscrabble streets and adobe houses—it is zero degrees centigrade. We breathe into the locks on the motorcycles to unfreeze them.

We head out of town as dogs watch us from the rooftops and alleys, and we begin to ascend a winding road. We enter a cloud of mist, emerging at about 3,000 meters with the cloud below us blazing white in the sun. We continue over a 4,700-meter pass, the temperature gauge on the bike showing minus 10 degrees centigrade. If we were on a commercial flight, in a cabin without pressure, oxygen masks would be dropping out of overhead compartments.

The ride across the Altiplano is awesome, empty and strange. We pass salt flats, white discs in the middle of vast open spaces, and dark blue lagoons that draw color from the sky. Vicuñas and llamas graze on rare patches of grass. We pass the skeleton of a horse still wearing its skin, propped up as though it were sitting on its rump. Someone has decorated it with flowers and flags.

The quality of the air, the clarity of the light.… This is as far from the eye chart in a doctor’s office as it is possible to be. Up here I can see farther and in greater detail than I have in years.

Day 22, Bolivia: We arrive in Uyuni around midnight to a hotel without power, heat or lights. We sleep in our riding clothes for the second night in a row.

The power outage lasts three days. Cars and buses line up at the two gas stations, waiting for the pumps to light up. We tour a graveyard of rusting trains abandoned in the 1950s. The sand drifts halfway up the steel wheels, burying the tracks. On blood-red metal someone has painted the phrase My heart is burning alive.

Standing on a downtown corner, Andres and Newts make a sign that says in Spanish “Will pay twice the going rate for gas.” Within five minutes a guy leads them to a 50-gallon drum in his backyard. We suction fuel through a hose and pour it through plastic Coke bottles cut into funnels.

We leave town for another day of gravel, construction detours, water crossings and animal hazards, arriving in Potosí, a 400-year-old city built on mineral wealth—silver hauled from the ground. Three weeks into the journey, my riding suit has developed a personality. I picture the end of the ride, standing the suit at a bar, buying it a drink, slapping it on the back and saying, “You’re on your own.”

We buy dynamite from a street vendor, a young woman who cuts fuse cord and short stubby sticks of explosives. She reaches into her apron for blasting caps. Total cost: about $2 an explosion. One of the Aussies who have joined our group sniffs the dynamite and says it doesn’t smell of cordite like the stuff he buys at home.

“What do you use it for at home?” I ask.

“Family arguments.”

Our guide helps us set off one of the sticks in a stone field. The concussive fist of air triggers something in each of us.

That night Newts makes another sign, drawing a stick figure of a woman with large breasts and a bottle with xxxx, the universal sign for booze. He flags down a taxi and gives the sign to the driver. In the morning the survivors can barely recall: a flashing neon sign, a dance floor, women and someone, Newts probably, saying, “Wanna bet I can get thrown out?”

Day 26, Bolivia: On the outskirts of La Paz we roll past a block of stores with steel grates on their windows. Out of the corner of my eye I notice an effigy—a human figure fashioned from gray fabric, filled with rubber blocks or garbage or something more dreadful, strung up by the neck 20 feet off the ground. A phrase is painted on the chest in red paint. Looking down the block I see an effigy on every lamppost.

I ask someone at the hotel about the effigies. The answer: “Theft is a big problem in Bolivia. The police are corrupt or inefficient. The merchants know if you hand the thief over to the authorities, he will be back the next day, angry. So they hang them. Or burn them.” Thirty-five thieves have been hanged in the preceding year. At a festival at a nearby beach resort, eight youths followed a woman into an alley. They grabbed her necklace and tried to pry the earrings from her ears. Two boys saw what was happening and ran to the town square. The community descended on the youths and, angered by the marks on the victim’s neck, poured gasoline on the thieves and set them afire.

We store our motorcycles in a secure compound, then take a taxi to the hotel. I walk the city. The shoe-shine boys, ashamed of their profession, wear ski masks to hide their identities. At intersections citizens dressed in zebra costumes leap about. Actors in donkey suits follow jaywalkers. A museum diorama shows one of the heroes of Bolivia being drawn and quartered—pulled apart by horses.

Rob and I visit the witches’ market, a narrow street lined with stalls selling totems that promise to protect you on a journey, bring love and prosperity and make your pecker grow. Outside are llama fetuses hung by the dozen and dried piranha, their mouths gaping, arranged on spikes to be used as offerings to God.

We are looking for something else, a map to the Road of Death. We hire a taxi driver to guide us through La Paz traffic to El Camino de la Muerte. It’s just me and Rob. No one else in the group will go.

Day 28, Bolivia: The Road of Death was constructed by prisoners of war from Paraguay in the 1930s. It is a ledge strung across a nearly vertical swath of the Andes, a slippery strand of mud and gravel, barely a car and a half wide, prone to landslides and fatal rockfalls. Above the road, a steep, overgrown, almost vertical mountain. Below the road, a 2,000-foot precipice. No guardrails between.

This very morning I read a news story about a bus plunge that took 17 lives. The reporter used an odd phrase, saying the bus “fell off the Andes.”

I turn on the helmet cam and head downhill. The government has closed the route to trucks; it is now maintained as a thrill ride for oxygen-starved mountain bikers. Without the oncoming trucks or the taxi drivers adrift in an alcoholic stupor, the Road of Death is just another road with an incredibly steep drop-off.

Rob wills himself not to look at the edge (on a motorcycle you go where you look) and rides close to the cliff face. I ride with the helmet cam aimed at the edge. It catches details that in my focused state I miss. The soundtrack picks up the sound of my breathing, the rattle of water hitting the bike as I pass waterfalls, a muttered prayer: “Don’t look down.” The wide-angle lens imposes a frame on the view, a frame that magnifies the blur of details that indicates speed. When eventually I see the footage, I crawl out of my skin.

Day 31, Peru: On the road from Puno to Cuzco, we gallop across the landscape at 90 to 100 miles an hour. We pass beneath the relics of glaciers hung out like skins to dry in the sun.

And then we hit a traffic jam. We edge past a long line of stopped gas trucks to where large rocks lie in rows across the road. The hills are covered with locals out for the entertainment. This is a roadblock, the first of many.

No one can tell us the cause of the ­protest—natives close the artery to express discontent over the outcome of soccer matches, the price of gasoline, government attempts to regulate the coca industry. Strikes can start on one side of Lake Titicaca and sweep the nation. We may be stopped for hours or days.

Our guide, Micho, negotiates with the locals. I take their laughter as a good sign. A deal is struck. We will carry villagers to the next roadblock. Two girls climb on one bike; an old guy climbs on behind me, giving a toothless grin to every person on the side of the road as we move out. It is a great frolic, until the last roadblock.

The organizers (oddly, all women) deny us passage. They scold the girls, who reluctantly climb down from our bikes. The mood changes in an instant. The women, all jowls and crossed arms, threaten to stone us, douse us with gasoline and set us afire. The threat needs no translation.

We backtrack and run a small roadblock guarding a side road. It is a rumor of a road, a blade-cut swath up the side of a mountain that supposedly leads to Cuzco. We crest the mountain and find ourselves in unspoiled Peru: farms, sheep, schoolkids pushing bikes, cattlemen on horseback. We buy gas from a woman in a cowboy hat who goes into her house and comes out with a pitcher filled with fuel.

Somewhere in this mad passage we lose Rob. Riding ahead, he takes a wrong turn and ends up back on the highway of roadblocks. He plays dumb, riding past the protesters, saying, “No entiendo” (“I don’t understand”). A boy throws a wire net under the wheels of the motorcycle, which wraps around the chain and brakes. Rob cuts it free with his Leatherman and beats us to the hotel.

Day 39, Peru: I depend on my cameras. They have autofocus; my eyes do not. At night I review the images like a pilgrim counting prayer beads:

A girl with cutoff shorts in a bar watching a soccer game, the flag of Brazil worn like a garter on her lean, tanned thigh.

A young boy leading blind musicians home at the end of the day, one hand on the shoulder of the person in front.

We sit at a café in Arequipa, comparing images on our digital cameras. Independently we have each taken a picture of a policewoman directing traffic on the town square, her motorcycle parked nearby. She is a striking figure, wearing the skintight khaki stretch pants and high boots favored by CHiPs. A policewoman with visible panty lines makes an arresting authority figure. None of us photographed her face, just that perfect ass.

I retire to my room to edit the picture. I have been on the road too long.

Day 40, Peru: We descend toward the coast. For three weeks the bikes have been starved of oxygen. Now they romp.

The road out of Arequipa twists through a lunar landscape where nothing grows. The colors—gray, tan, white—are the dust and rubble from ancient volcanoes, worn to stumps. The shrines begin almost immediately. In one 95-mile stretch I count 147 crosses. They are easy to spot. Other than the power line to our left, the black-and-white kilometer posts and the shards of truck tires, they are the only man-made objects in view.

Here someone went off a corner through a guardrail. Here someone didn’t see the oncoming curve and augured into the mountain. There are shrines at almost every service station and store. And then there are those that dot the long straits. Every point where someone asked something of their vehicle and it failed. This is the real highway of death. And at each shrine I hear my heart beat its mantra. Not me. Not yet. Not ever.

We crest the last range of mountains and feel the cold breath of air coming off the Humboldt Current. John, Rob and I split off from the group for a private celebration. We set the bikes loose in the sand, performing burnouts, sending rooster tails skyward. But quickly we become subdued. How will we describe this journey to friends and family? I set the timer on a digital camera for a group photo with motorcycle. Every day of the ride is visible on our faces. Below us the Pacific applauds.