The Importance of Good Vision for Driving & Minimum Vision RequirementsUpdated Sept. 16, 2019
No sense is more important to a driver than vision. As your eyes are responsible for 90% of the information you receive while driving, good vision is essential in making safe and appropriate driving decisions. You must be able to pick out fine details in the roadway environment at a distance, including road signs, other vehicles, cyclists, traffic signals, pedestrians and motorcycles, in order to drive safely.
While driving, you must continually collect, process and act on visual information. If any link in this chain is weak, you may not be able to react quickly enough to avoid hazardous situations as they arise. This is why good vision is so important. If you cannot see a hazardous situation soon enough to assess the situation and react, there is little you can do to avoid a collision.
To give you an example of this problem in action: a car traveling at 55mph in favorable weather conditions will need around 400 feet to come to a complete stop. Therefore, if you cannot clearly see at least 400 feet ahead of your vehicle while traveling at this speed, you would not be able to stop in time to avoid an obstacle on the roadway.
Now, let’s learn a little more about how we use our vision while driving.
The most important part of a person’s vision is referred to as central vision. With good central vision, you can pick out fine details by focusing your eyes on a specific spot. This type of vision is essential for reading, writing, recognizing faces and of course, driving. Any activity which demands precise, sharp, straight-ahead vision relies on central vision.
Central vision may be impaired if the eye’s macula is damaged by age, illness or injury. This essential part of the retina is full of sensitive photoreceptors known as cone cells, which provide straight-on vision. When cone cells cease to function as well as they should, a person’s central vision will suffer.
Visual acuity is the ability to accurately perceive objects and pick out fine details and colors. A person with healthy central vision will have visual acuity. Without visual acuity, your ability to read road signs, spot hazards and identify objects on the roadway would be adversely affected. It is, therefore, essential for driving.
As visual acuity is so important, all prospective drivers must pass a visual acuity test using a Snellen chart when applying for a license. This chart features rows of random capital letters which will decrease in size as you move from top to bottom. You will be asked to recognize each letter in turn, until you can no longer make them out. If you do not meet the minimum eyesight requirement to drive, you will be issued a “restricted license”, whereby you are legally obligated to wear contact lenses or glasses while driving.
How is vision measured?
If you can recognize letters that are 3/8” tall from a distance of 20 feet, you are said to have 20/20 vision. This is ideal, healthy vision. A person with impaired vision would need to be closer to an object to perceive the same level of detail as somebody with 20/20 vision. For example, having 20/40 vision means that you can see the same level of detail at 20 feet as a person with 20/20 vision can see at 40 feet.
Minimum vision requirements
The minimum vision requirements which drivers must meet vary a little around the United States, so be sure to check your state’s driving handbook for local information. Drivers may be awarded a full license or a restricted license (stipulating that they must wear glasses). When vision is extremely poor, a person may not be eligible to drive at all.
Being near-sighted or far-sighted
Generally, when somebody has a vision problem it presents as near-sightedness. Near-sighted people can see just fine when they focus on close objects but struggle to make out detail when they look at something farther away. Near-sightedness ranges from 20/40 vision to 20/200 vision.
In contrast, far-sighted people struggle to focus on nearby objects but have no trouble seeing distant objects clearly. If you are far-sighted, you will still need to wear glasses or contact lenses while driving. Perceiving far-away objects is important, though it is just as important that you can see objects within the car clearly, like your speedometer. The bottom line is that any vision problem must be corrected with appropriate eyewear before you can be safe to drive.
The cells around the outside of your retina are responsible for side vision, or peripheral vision. Peripheral vision allows you to perceive objects, colors and movements without looking directly at them. Though your peripheral vision is not as detailed as your central vision, it makes up a large portion of your total vision and is essential to your perception. You may be shocked to hear that your central vision only accounts for about 3° of your vision while peripheral vision accounts for 180° or more.
Good peripheral vision is vital to drivers, as it allows us to perceive vehicles moving in adjacent lanes while looking straight ahead. It also makes it possible to keep stock of events in front of the vehicle when we briefly turn or check our mirrors.
It is important to note that the range of your peripheral vision will decrease the faster you are traveling. You must compensate for this when traveling on high-speed roads, by turning to scan through your side windows more frequently that you would otherwise.
As we rely heavily on our central vision, many people do not notice that they have a peripheral vision impairment. Unfortunately, a peripheral vision impairment will make driving considerably more dangerous. For instance, poor peripheral vision may lead you to:
- Fail to see a vehicle approaching dangerously from the left or right side
- Not notice a traffic light suspended above eye-level at an intersection
- Pass parked cars too closely
- Fail to see a cyclist or motorcyclist in an adjacent lane
- Cross over into an adjacent lane while driving through a curve
While you can perceive a great deal through your peripheral vision, you must not rely on it completely when monitoring events to the side of your vehicle. Turning to check your blind spots and checking your side-mirrors every so often will give you a clearer picture of what is happening on the roadway around your car.
Depth perception describes how well you can see in three dimensions. A person with poor depth perception will have trouble determining how far away objects are. This would be problematic when judging the distance between your vehicle and other vehicles or objects on the road.
Depth perception can be adversely affected by some medical conditions, though it can also be impeded by environmental factors such as darkness and fog. A driver with poor depth perception may stop short of or over-run stop lines at intersections, turn too sharply or widely and fail to maintain a safe following distance.
Get regular vision checks
Whether you drive with a restricted or unrestricted license, you must monitor your eyesight and address any changes which occur throughout your driving life. It is important to get vision and eye-health checks regularly, otherwise you may not notice near-sightedness or problems with your depth perception developing until they reach a dangerous level.
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