If you have macular degeneration , you may have struggled over whether to continue driving. The disease, which affects one in four people over the age of 65, does not cause blindness, but it does cause blurriness or a blind spot called a scotoma in the center of the field of vision. The size, density, and location of a scotoma determine whether you can see well enough to drive safely.

Deteriorating Vision

It's tempting to just continue driving until you're denied a driver's license, but your vision could deteriorate long before your license expires. For safety's sake, most people need to make the decision themselves, says Yale Solomon, MD, who, together with his son, Jonathan, wrote the book Overcoming Macular Degeneration: A Guide to Seeing Beyond the Clouds . As an ophthalmologist, he treated hundreds of people with the disease before being diagnosed with it himself in 1990 at the age of 64.

Knowing When It's Okay to Drive

To drive safely, you must not only meet the visual acuity requirements for having a driver's license, but also have good reflexes and a good field of vision, so that you can react to an unexpected event, such as a child darting from between parked cars.

You don't have to see everything perfectly in focus. "A person crossing the street might look slightly blurry, but you don't need to see if they're smiling at you," says Dr. Solomon. If you're in doubt, test yourself. Go out with a family member or friend on a bright day when traffic is light, and test your ability to turn, avoid obstacles, and park.

Driving at Night

Many people who are able to drive during the day may have difficulty driving at night, because of reduced contrast sensitivity .

"If a patient with macular degeneration looks at an eye chart with black letters on a white background in a bright light, he might be able to read at 20/40 or 20/50," says Dr. Solomon. "But reduce the contrast by making the background gray and the black letters dark gray, and bingo! The acuity suddenly drops to 20/70 or 20/80, but a person with 20/20 vision can read it at about 20/30."

Optical Aids

The autofocus spectacle-mounted telescope won't compensate for an inability to see cars and people, but it can help drivers read signs. One model flips down over the top of eyeglass lenses, and the object viewed through it comes into focus automatically. "It's a tremendous advance over fixed-focus devices that focus only when an object is at a particular distance," says Dr. Solomon.

Using these prescription telescopes, also called bioptics, requires training at a low-vision clinic. Dr. Solomon notes that it can take months of practice to get used to them.

Driver's License Requirements

Most states, but not all, require that vision be corrected to 20/40 in the better eye for obtaining an unrestricted driver's license. (With 20/40 vision, the smallest letters you can read on an eye chart from 20 feet away could be read by someone with 20/20 vision from 40 feet away.)

Tom Perski, executive director of Macular Degeneration International, says that most states accommodate people with low vision by issuing restricted licenses that limit driving to daylight hours. And some states offer restricted licenses that allow people to drive only to certain locations.

"I think the trend is for states to be more open-minded about looking at this issue," says Perski. "For example, more states now allow drivers to wear bioptic lenses."

Families and Other Support

"Families must have enough trust to talk about driving openly," says Dr. Solomon's son, Jonathan. "At some point, say a rainy, foggy night, a loved one may have to say, 'Let me drive,' and be confident enough of the relationship to request or demand it. The nightmare is that there could be a tragic accident."

When families and friends cannot provide transportation, people can often find drivers through support groups and volunteer organizations.

The Loss of Independence

Dr. Solomon acknowledges that being unable to drive can be traumatic.

"It's a personal and public proclamation that you've become less independent, less capable and more reliant on others. As agonizing as it might be, you look into other areas of satisfaction that don't involve driving. Life does not equal driving. That's why I subtitled the book A Guide to Seeing Beyond the Clouds ."

If you have any decrease in your vision, be sure to talk to your eye doctor before driving.