For anyone who relies upon eyeglasses for everyday vision, the problem of fogging is a common and well-known nuisance. In cold weather, the effectiveness of eyeglasses is often rendered null through fogging, with moisture droplets collecting on lenses and obscuring sight. To prevent this from happening to you, adjust the conditions that cause fogging or treat your glasses to keep water from collecting upon them.
Position winter clothing to prevent fogging. If you struggle with glasses fogging due to the heat and moisture of your own breath during cold winter weather, check to see if any winter clothing is directing air from your nose and mouth up to your eyes. Remove scarves or winter face masks that are wrapped so that the air is escaping out and upward, or rewrap them so that the air escapes downward. Alternately, wear a scarf with a coarse enough weave that air can escape through the knitting itself.
Transition from cold to hot areas gradually; fogging happens because water molecules in the air are attracted to a hard surface that's much colder than the ambient temperature. In buildings, stand near doorways or inside walkways where the air will be cooler than inside, but warmer than outside. Wait for a minute or two, then go in; the gradual transition will keep the glasses from fogging. If riding in a car, let it heat gradually. (Though this is generally less practical than simply removing your glasses to wipe them, it's a good solution for times when your hands aren't free.)
Coat your glasses with a solution of three parts water, one part white vinegar. Rub the solution on both sides of your eyeglass lenses and let dry (do not rinse or wipe away).
Treat your glasses with commercially made anti-fogging solution. This is an inexpensive liquid that comes in a portable pump spray bottle. Spray on both sides of the lenses to coat them, then let dry. Carry the bottle with you to reapply as needed.