by Edward J. Huggett, O.D.
I am often asked, "How long is it safe to drive when your vision is deteriorating?" There are three visual factors that are important to consider when it comes to driving. Visual acuity (VA), visual field (VF) and contrast sensitivity (CS). There are others I will not cover here, such as eye movements, useful field of view, depth perception, color vision and eye-hand/foot coordination, etc.
So for driving, let us consider: (1) visual acuity, typically known as the "20/20" or "20/40", etc. measurement and (2) visual field, which is the extent of your field of vision and the size of the area of your vision that has no significant defects such as scotomas. If you are in the United States, your state will have a very definitive statement as to what these two requirments are. Requirements can be found for your state at www.mdsupport.org/library/drivingrequirements.html. Not meeting either one of these requirements at any time indicates that you should not drive.
Secondly, I would say that if at anytime you are not feeling safe, then it is time to stop. So, even if your vision is "perfect" and you meet the legal requirements for driving, if you feel like your vision isn't good enough to drive, then don't.
If your vision is deteriorating, then you may need to visit your eye doctor or department of motor vehicles more frequently, sometimes every few months, to determine if you still meet the legal requirements for driving. Typically, eye doctors are the better place to go, as they can determine if your visual field is adequate for driving. Most department of motor vehicles cannot measure that important function of vision.
Certainly, driving under ideal conditions is very different than driving at night, in the rain or snow, or in poor light. Also, glare from headlights or the sun can be a problem. Studies suggest that if drivers are prepared to compensate for aging eyesight by adjusting their driving habits, then deteriorating vision is not necessarily a barrier to safe driving. Changing habits may include:
1. Driving only in daylight or on well-lit roads
2. Driving only in good weather
3. Driving only in the familiar local area
Generally, the best sunglasses are those that wrap around and protect the eyes from the side as well as the front. A neutral grey tint is usually best, as it doesn't alter the color of traffic signals. But I have found that "blue blockers" or another called "shooters yellow," can increase comfort, contrast sensitivity and ability to see during the day. Polarizing sunglasses can also be helpful. Only through trial and error can you know which color of sunglasses are best for you. You will find a good deal of information about sunglasses at www.mdsupport.org/library/sunglasses.html
Sunglasses or tinted glasses are never recommended for driving at night. While they may seem to reduce glare from headlights, they also make everything else darker too. At night your eyes need more light, not less.
Make sure your windshield is clean and scratch-free, both inside and out, at all times. In many cases, even small cracks in your windshield will be a covered benefit for replacement by your auto insurance. Contact your auto insurance company to find out.
Ask your mechanic to check that your headlights are correctly aligned to provide good road illumination, while not causing glare for other road users. Look slightly to the left of oncoming traffic at night to avoid suffering from glare which can take some time to recover from.
Any scratches or smudges on your driving glasses (or sunglasses) will increase glare, so keep them clean! Additionally, AAA has a very nice section on their website at www.aaaseniors.com. This area provides excellent information and an online skills assessment for the mature driver.
Remember, if your vision does not meet a safe legal standard, driving will put the lives of others at risk, and your insurance may be void in the event of an accident. But if you meet the requirements, if you are safe and feel safe, and you have somewhere you want to go, then drive and have fun!