There are some lens coatings that provide anti-fogging and under 'normal' conditions, they work quite well. You can get also sports glasses with special anti-fog lenses.

Outside, fogging normally occurs when warm air (such as your breath) is deflected upwards towards your specs - such as wrapping a scarf around your mouth and nose. The warm air condenses on your cold lenses and steams up. The obvious solution is to move the scarf down a bit and let the warm air dissapate

You can buy anti-fogging wipes - these basically create a layer between the lens and the outside world. Other suggestions are a drop of shaving foam or soap wiped over the lens and 'buffed off which do the same as the anti-fogging wipes. However, soaps with microgranules in them could damage the lens and we wouldn't really recommend any of the above.

However, in the extreme weather we have at present, nothing is going to be much use. Stepping from a very cold environment into a warm house, car or office is going to make them steam up regardless!

A quick wipe with a good lens cloth will take the surface moisture off the lens and help warm the lens up and so reduce the incidence of condensation.

But do not attempt to drive until your lenses are clear!