Next time you find yourself out on the road at night, consider this: Somewhere around you--the next lane over, behind you, or maybe in oncoming traffic--is a driver so impaired that he may have no business behind the wheel.
He’s not a drunk driver, although there may be one of those around too. The driver we’re talking about is stone-cold sober. He just has trouble seeing what’s going on around him.
Remember the last time you drove in a heavy rainstorm, squinting to get a glimpse of the road between wipes of the windshield? That’s what it’s like for this guy every night, except he doesn’t even have wipers to clear things up for an instant here and there. Instead, the glare from oncoming cars washes intermittently across his eyes, temporarily blinding him.
But as far as he knows, his vision is perfect. He aced the eye chart at the Department of Motor Vehicles, and he could ace it again tomorrow. Night driving probably bothers him, but he may have no idea he’s such a menace--and neither may the rest of us.
“The standard eye chart--you know, the one with the big ‘E'--is useless” when it comes to assessing nighttime vision, says Dr. Clifford M. Terry, an ophthalmologist with offices in Fullerton and Anaheim, who also serves as an adviser on vision testing to the DMV.
And no wonder. “That test was developed before the Civil War, in the 1850s. That was before we had cars, before we had light bulbs,” he says.
Al Lohrmann, driver improvement manager for the DMV in Sacramento, says the agency is well aware of the problem. In fact, the DMV is just completing a 2-year study on the subject. “We’re looking into what we can do to improve our screening,” Lohrmann says.
The “E” chart measures only one aspect of vision: acuity, or the ability to see things in clear focus. But it does nothing to check two other factors that can make a big difference in night driving: contrast and glare.
With black letters on a white background, the old-fashioned chart has plenty of contrast. And that’s just the trouble, Terry says: “Real life is not black and white but many shades of gray.” And when the sun goes down, there’s even less contrast, he points out.
“We need people to be aware that even a person with the best of vision does not see as well at night as they may think they do,” Lohrmann says. “We tend to have a false sense of security. Many people over-drive the distance that their headlights cover. They may not be able to see a person in front of them in time to react. But most of the time people on the freeway are going the same speeds they go in the daytime.”
For some, especially older drivers, the problem is made worse by what’s called a contrast defect, Terry says. They just can’t perceive the more subtle differences in shade--differences that become all the more subtle at night.
“As we age, the lens (of the eye) begins to lose some of its optical clarity,” Terry says. “In the daytime, it doesn’t matter so much; it’s like wearing sunglasses all the time.” But at night, it’s still like wearing sunglasses, he says, and that’s the problem.
According to cases Lohrmann found during his 2-year study, a 60-year-old may need 10 times more light to see than a 20-year-old.
Then there’s glare. “Certain people, when they see a light, they see a halo around it, or multiple lights,” says Terry. “They’re temporarily blinded and can’t see to react.”
Both contrast and glare defects are most often caused by changes in the lens that can eventually lead to cataracts. “It can be one of the early signs. But there are many more people who have nighttime driving defects than people who have cataracts.”
The problems are most common in those over 60. “By age 65, about 1 in 5 have some difficulty with it,” Terry says. But they can happen in younger drivers as well. He recommends screening all drivers 45 and older.
But other factors can affect drivers of any age.
“People who wear contacts or glasses have more nighttime problems,” Terry says. “Light is scattered as it passes from the air to the lens to the cornea, and that causes more glare.”
People with astigmatism can see “tails” on some lights at night, and those who are developing cataracts may see halos, Terry says.
Light-sensitive individuals have problems at night too. “The glare from the headlights around them makes them uncomfortable,” Terry says.
One possible solution is special glasses with gradient lenses, heavily tinted at the top and clear at the bottom. Terry is currently doing research with such glasses using Orange County drivers. “When there are headlights, you dip your head down and look through the top portion,” he says.
Terry also would like to see curbs painted to be brightly reflective, or at least in contrast with the road around them.
There are ways of measuring contrast and glare defects, including the Terry Vision Analyzer, invented by Terry, a computerized system now used by more than 700 eye care professionals. The device uses as many as 20 shades of gray and has random letter sequences to thwart those who try to memorize the chart.
Lohrmann says Terry’s analyzer is one of several such devices that the DMV is considering using for driver vision tests.
One concern the DMV has is the amount of time involved in testing. The current testing method takes only about a minute, Lohrmann says, “and some of these (possible alternative) tests would take 20 minutes just to check one vision variable. To do that for everyone is unreasonable.”
Testing with Terry’s device takes about 15 or 20 minutes, he says.
With about 3 million driver licenses being issued each year at 162 offices in the state--not including those licenses renewed by mail, “we would need more people and more space to be able to do expanded testing,” Lohrmann says.
In the meantime, Terry suggests, if you have a problem, get it checked out with an eye-care professional who has the kind of equipment the DMV doesn’t.
And all of us should keep our windows and windshields clean to reduce glare. Wouldn’t hurt to wipe off the headlights, too, so that they’re working at full capacity.
And Ken Daily of the California Highway Patrol’s San Juan Capistrano office reminds us that headlights must be on when we’re driving anytime from half an hour after sundown to half an hour before sunrise.
Daily also points out that improper use of high-beam headlights is more than impolite--it’s against the law. Turn those lights down whenever an oncoming vehicle is 500 feet away or closer, or if you’re following within 300 feet of another vehicle.
“Use your lights other times too,” Daily says. “During inclement weather, or even on a really overcast day. It isn’t just what you can see, but you want the other cars to be able to see you.”
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