Why does my vision change?

[mrs_overall]

I wear glasses for distance vision and need them for driving. However, when it is dark I can actually see better without them. Why is this?

[douglas9401]

Are they prescription sunglasses? :)

[mrs_overall]

Not sunglasses, just ordinary prescription specs. I wear them for watching TV and driving (although not at the same time lol)

[tonyav]

Perhaps your vision changes after you have had a '' drink '' ?.

[mrs_overall]

I don't drink & drive so that theory is no good tony :-)

[tonyav]

Oh ok then lol.

[Kiki-frog]

Because you're a special person with superpowers of vision. You should be wearing a cape, tights and knickers on the outside and ridding our streets of crime.

Seriously, I don't know, but my night vision is better as well. I know it's to do with the relative strengths of the photoreceptor cells, rods and cones, but that's about it.

[york310]

I think you at probably slightly long sighted most likely by approximately +1.00ds . This means that you have to focus this much to see in the distance clearly. Most people, up until probably their mid fifties, manage to focus this amount by themsves without the need for this small distance correction.
However, when it goes dark or from about dusk time, everybody experiences a small shift in their distance prescription which is a myopic shift from pupillary dilation. This effectively reduces your +1.00 to probably about a +0.50D which in turn means your unaided distance vision is better without specs and that your specs would be too strong and probably blur your far distance vision.
A lot of waffle - google night myopia.

[mrs_overall]

Thanks york - an interesting and concise answer that explains it well