Naked Science Forum
General Science => General Science => Topic started by: PAOLO137 on 10/07/2015 10:42:56
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When I have to renew my driving licence from time to time, I must undergo a visit by a doctor, who, using the usual table with letters or symbols getting smaller and smaller , until he decides that I'm "almost blind" and cannot drive a car.
After leaving the place, I start driving and I am sincerely sure I'm able to see every detail of the environment around me, a bug crossing slowly the street, leaves on trees, read an advice stuck on a tree , the model of the bag of the old lady crossing the road.
This makes me very upset. How could the doctor argue I cannot drive?
I am a physicist, so I like to compare experiments. This one is like measuring something using two different methods. Suppose to have a pot of boiling water, putting a thermometer in and measuring
60 degrees Celsius. One of the two concepts is obviously wrong : water doesn't bubble or the thermometer isn't good? Unfortunately the doctor will prevent me to drive, according to awrong concept Thanks, Paolo
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Time to visit an optician.
Not sure where you live, but the UK rule is "able to read a car registration at 20 meters, with spectacles or contact lenses if normally worn ". A short-distance reading test is obviously irrelevant.
There is an additional test of distance perception if you are blind in one eye.
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Your kind replay confirms my opinion on British people as intelligent, since the year when I spent one month there as a student in 1960. You simply confirmed that if I must be evaluated in a situation, whichever it is , the test must take place in that same situation.
I'm sorry to be aware of this, but i am ashamed of being Ialian. We excel in pizza, mafia and spaghetti, forget the rest.
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Apparently some people who are totally blind are convinced they can see (https://en.wikipedia.org/wiki/Anton%E2%80%93Babinski_syndrome) : their brain is confabulating sight.
If that is possible then the brain of someone whose vision was too poor to drive could invent detail in what was a blurry picture.
People who have tunnel-vision (https://en.wikipedia.org/wiki/Tunnel_vision) don't notice it until it's at an advanced stage : their brain compensates for the loss of peripheral-vision up to a point, but eventually it becomes apparent that their peripheral-vision is out-of-date.
Another eye-test from an optician/opthalmologist will tell you whether your doctor's assessment of your vision is correct.
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In a conversation with a woman who had her cataracts corrected by surgery, she mentioned that she didn't think that her vision was that bad, but was astonished with the detail she could see after the operation.
A degradation which progresses slowly does not allow you to perform an A/B comparison experiment - but when it is corrected suddenly (such as with surgery, or even better with the right prescription glasses), you can compare the before and after condition.
From the point of view of driving safety, it is more important to be able to see another car, and avoid it, than to read its number plate accurately. However, it is also important to be able to see the driver's face, and to recognise whether he has seen you, and this requires acuity similar to the ability to read a number plate.
Although your optometrist's office may not be 20m long, they can make use of mirrors to position the eye chart at the right distance from your eyes.
With other optical arrangements, they can test your ability to focus on close-up objects and ability to read fine print. But the most important visual skill for driving is long-distance vision.
How good are sight tests as a guide to driving ability?
Driving ability involves many skills beyond vision, including experience, awareness of dangers, etc.
However, if you can't see, then you can't apply your experience to the current situation.
With degraded vision, you may be able to apply these skills learned by experience, but it may take longer to focus on objects, read signs in new areas, or recognise a dangerous situation, and may result in cautious people driving slower than usual (and from what I observed in Italy, driving at the speed limit means you are driving slower than the usual). It may also result in adventurous people having more accidents than normal.
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Surveys show that the vast majority of drivers (or teachers) consider themselves to be above average.
With normal distributions (which are close to Normal distributions), about 50% of people will be above average.
So we are not very good at assessing our own capabilities - and perhaps that is protective, as people need some self-esteem.
To get a more objective view of my driving ability, I installed a "Safe Driver App" on my smartphone. It tracks braking, acceleration and conformance to speed limits, among other things, and gives you a star-rating for each journey. It creates a "fingerprint" of your driving style, and is quite good at recognising when I am in a car, but someone else is driving.
This App was advertised on TV by an insurance company, making it available to the general public, with an offer of free roadside assistance if you scored above 60/100 (and an implicit hope that good drivers will transfer to their insurance company!).
I know similar Apps are available in the UK, but I don't know how popular they would be in Italy.
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It's entirely possible that the distribution of driving ability is such that most people are better than average.
(Most people also earn less than the average salary for their country and almost everybody has more than the average number of legs.)
All it takes is a handful of truly awful drivers in addition to a roughly normal distribution round "ordinary driving ability" to reduce the average below the peak of the distribution.
In answer to the question in the thread title, I can see just fine: 20/10 vision with my glasses on. But I don't drive; I tried learning but I'm poorly coordinated and have slowish reflexes.
The best advice seems to be to go and see an optician.
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From the point of view of driving safety, it is more important to be able to see another car, and avoid it, than to read its number plate accurately.
This may be the case Down Under, but the reading test is necessary over here because statutory road signs are designed to the same standard of visual acuity.
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The sight tests are made to test if your seeing is 100% accurate. You should be able to see every road sign that can contain text from a big distance to avoid any problems.
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My understanding is that they are not looking for 100% accuracy in reading the eye chart - they can tell whether you are guessing, or just confusing two similar letters out of a line of 10 letters.
In Australia, they have experimented with a locally-restricted licence for people who have driven for a long time, and just drive down to the local shops to buy their groceries. In such cases, they have lived in the area for a long time, and they know the signs without having to read them. I imagine there could be problems if a two-way road is suddenly made 1-way and they can't read the sign; I have also heard of cases where people have driven far out of their approved area.
Bring on the self-driving cars!