Low-Vision Drivers -- Research Summary

WHAT IS LOW VISION? Low vision is defined as vision loss that cannot be corrected by regular spectacles or contact lenses, and is serious enough to be considered disabling.

LOW VISION MYTHS: Studies have shown that while vision is important to driving, poor or imperfect vision is not the major cause of most accidents. In fact, one study found good vision is associated with a poorer driving record. The most dangerous drivers, according to research, are young men who typically have excellent vision but exhibit poor judgment on the road.

OTHER FACTORS TO CONSIDER: While visual acuity, the ability to see objects clearly, is important, there are other factors relating to vision that come into play when determining whether someone can drive safely. These include:

Visual field -- the measure of peripheral vision; how far you can see objects that are off to the side of your direct line of view. If you can raise your hands from your sides and see both your hands while looking straight ahead, your visual field is 180 degrees. This vision allows us to detect moving objects off to the side. In most states, a visual field of 100 degrees or more is required to drive. Glaucoma can often restrict visual field. A person is considered legally blind when their visual field is reduced to 20 degrees or less.

Color vision -- a measure of how well you can distinguish between colors, especially red and green. About 10 percent of men and 0.5 percent of women have some kind of color deficiency. Only 19 states require color vision screening to drive. States with standardized traffic lights have the red light on top and green light on bottom so while a color deficient person cannot see the color of the light, they can tell which one is illuminated.

Contrast sensitivity -- a measure of the ability to detect low contrast stripes of different sizes. It is measured by the ability to read large letters of low contrast. While studies have suggested a connection between reduced contrast sensitivity and difficulty driving, no state requires contrast sensitivity testing to get a drivers license.

Glare -- a measure of how bright light, during the day and at night, affects your ability to see and drive safely. It is important for people with vision disability to acquire skills in selecting and properly using sunglasses or the car’s visors, and to avoid situations where glare can be detrimental to safe driving. There are no routine tests to measure sensitivity to glare.

Useful field of view -- A measure of visual field area over which one can process visual information that is presented rapidly and simultaneously in more than one place. These abilities tend to be severely reduced in the elderly. Also, a reduction in useful field of view is associated with a history of at-fault crash involvement. A person is considered legally blind when his visual field is reduced to 20 degrees or less but at the moment no state is applying tests to measure useful field of view.

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