Glasses and Driving?

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Dr. Wexler

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Hi,

Is there any research out there that shows at what point it makes and actual safety difference for a person to wear glasses?

I recently got a very mild prescription (-.75D and -.5D) and without them on, everything seems normal, but once I put them on, esp. at night I think "wow, things are much crisper now!".

I do feel safer driving with them on, but I was wondering, is there any research out there on the safety improvements of glasses vs. no glasses over various ranges of near-sightedness? Are there prescriptions that are so weak they wouldn't make a difference in terms of driving safety?

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i'd stear my research in that direction if i were you, and maybe look up stuff with the department of transportation

for CA you must were your glasses if you cannot see better then 20/40 without them. in a prescription this would be about a -1.00. BUT that's only an estimate.
 
iiiimonica summed it up.. I think most states are 20/40 minimum acuity in the best eye. If you're under a -1.00 in optimal conditions you may be ok.

The only other side to it is as flynnt said about feeling safer... especially at night, there's a phenomenon known as "night myopia" which there's a few theories about. It could be the purkinje shift, the increased pupil size, dark focus (1 meter) or a bunch of other ideas. So many people really notice their vision isn't as clear when driving at night. I've had -0.50 patients who say they feel fine driving during the day but at night they really feel "blind" without their glasses.
 
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iiiimonica summed it up.. I think most states are 20/40 minimum acuity in the best eye. If you're under a -1.00 in optimal conditions you may be ok.

The only other side to it is as flynnt said about feeling safer... especially at night, there's a phenomenon known as "night myopia" which there's a few theories about. It could be the purkinje shift, the increased pupil size, dark focus (1 meter) or a bunch of other ideas. So many people really notice their vision isn't as clear when driving at night. I've had -0.50 patients who say they feel fine driving during the day but at night they really feel "blind" without their glasses.

I thought driving w/o glasses was 6/12 (20/40) unaided VA in both eyes (what if the patient was amblyopic?)

Could night blindness (esp. in older patients with cataract) also be due to increased glare sensitivity from looking at street lights through the windscreen?

There are formal driving standards etc. but unfortunately I am unsure of the American ones. It's not only about prescription either, you have to have enough of a functional visual field as well.

Almost forgot: I agree that we have decreased spatial resolution at night as well.
 
I thought driving w/o glasses was 6/12 (20/40) unaided VA in both eyes (what if the patient was amblyopic?)

This varies from state to state. You're right in the UK it's 6/12 binocular. New York State is 20/40 in best eye, i.e. A monocular patient can drive if correctable to 20/40 in the good eye. Also the visual field required in New York state is 140deg horizontal, which again a monocular person could have.

Edit: I just did some googling to confirm.. and I do remember something from class! Here's the details for NYS: http://www.nhtsa.dot.gov/PEOPLE/INJURY/olddrive/OlderDriversBook/pages/NewYork.html
 
Thanks everyone. I di research and found my state allows people with 20/40 or better combined vision to drive without glasses as long as either eye is worse than 20/40.


Is there a chart anywhere that coverts diopetres to the typical measurements used in American (20/20, 20/30, etc.)? Or is there not an exact relation to dipoeters and the visual acuity from the Snellen chart?
 
A monocular patient can drive if correctable to 20/40 in the good eye.

Hahaha, yep - I think I meant with both eyes open, even if they have no vision in 1 eye. So does that mean the dominant eye will take over even if the patient is highly amblyopic in the other eye?
 
Thanks everyone. I di research and found my state allows people with 20/40 or better combined vision to drive without glasses as long as either eye is worse than 20/40.


Is there a chart anywhere that coverts diopetres to the typical measurements used in American (20/20, 20/30, etc.)? Or is there not an exact relation to dipoeters and the visual acuity from the Snellen chart?

I'm not exactly sure of your question, but I think you mean "if a patient is a -1.00 what would be your expected acuity?" If that's the question then we usually go by an ESTIMATE of one line acuity loss for every 0.25D, starting 20/20. So you'd expect around.. 20/40-20/50 for a 1D myope.


Hahaha, yep - I think I meant with both eyes open, even if they have no vision in 1 eye. So does that mean the dominant eye will take over even if the patient is highly amblyopic in the other eye?

I believe this is the case. As long as they have 20/40 in their best eye, it doesn't matter what the other eyes status is.. unless the 20/40 eye also has a reduced field, then the bad eye may come into play.
 
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