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On Driving: Issues Faced by the Low Vision Driver

In a world of instant gratification where people can just hop in the car and everything is at their fingertips, the loss of America's primary mobility tool can be devastating.  Many people are unable to drive to work or continue living in an area without public transportation.  People who have been independent for a lifetime must rely on relatives or friends to drive them long distances.  Since the driver's license is such a symbol of independence, the loss can be a psychological and emotional devastation.

Based on demographics from the 2000 U.S. Census, 2.4 million Americans (1.98%) have low vision (defined as greater than 20/60 with best corrected vision or visual field of less than 20 degrees in the better eye by the World Health Organization standards.)  A study sposored by the National Eye Institute (NEI) estimates that by 2020, the number will increase by 70% to 4.1 million.  The increase is primarily due to the aging U.S. population.  Due to this massive increase, it is imperative that professionals be as versed in low vision rehabilitation as possible.

The necessary skills to be a safe and independent driver are similar to those used fro pedestrain orientation and mobility (O&M).  If you want to travel through an environment, you must understand the environment.  You must understand the layout of the area, establish landmarks, and identify passing traffic.  Just as you would plan a trip using a road map, so must the visually impaired driver prepare for a trip before they travel in unfamiliar areas.  Cardinal directions are always important.  If the sun is not our, how would you orient to your surroundings?  That is where basic orientation techniques come in.  Various forms of GPS, assistive technology, and gadgets of the future are being developed to help drivers.  However, none of this will ever replace a simple map and compass.

Driving safely requires a number of important skills such as: ability to perceive changes in a rapidly changing environment, managing to judge and take action on the information in a timely and safe manner, and the motor ability to take the actions needed.  The useful field of view (UFOV) is defined as the area where one can take a quick glance to extract visual information without head or eye movement.  Problems resulting from a reduced UFOV include slowed reaction time, decreased visual attention, and problems processing "visual clutter".  If one are is diminished, it is up to the driver to compensate in another area.  For example, if there is a problem perceiving changes in the environment, it will become imperative to compensate by taking a quicker action.  Braking at a stop light is a mixture of identifying the sign, then applying the brake.  If you perceive the sign later than average, you must apply the brake sooner than normal.  A complex and busy visual environment may be confusing to a driver, with hazards overlooked.

There is far more than simple visual acuity involved in the complex task of automotive travel.  Many people need practice scanning and spotting the various indicators that allow a person to maintain a proper distance from other motorists.  The person must locate intersections, traffic signs, and estimate distance using a variety of techniques.  For example, when a motorist is not present on a  perpendicular street, how would a person identify that intersection?  These are the types of concepts that orientation and mobility specialists teach.  Many people with a loss of depth perception have to pay attention to other visual cues.  Visual trailing of the sides of buildings, grass-lines, and curbs all play an important role in low vision adaptive driving.

A topical study found that low vision drivers have deficits with visual processing speeed, reduced contrast sensitivity and visual field sensitivity.  The same study also found that highway travel was not significantly different for the low vision driver and sighted drivers.  With these findings, it can be said that by practicing adaptive behavior, low vision drivers can be safe drivers.

"On Driving: Issues faced by the Low Vision Driver", Tyler C. Hamilton, M.A., COMS, Visibility, Volume 3, Issue 2, May 2009; originally produced by the Envision Foundation, 610 N. Main, Wichita, KS 67203, www.envisionus.com.