Nearly 50% of Americans wear corrective glasses, according to the trade group Vision Council. And most of them are guilty of the biggest crime in lens care: Exhaling onto their lenses, then wiping the fog off with their shirt sleeves. But does this really damage your lenses? Teri Geist, an optometrist in Omaha, Neb., and chairwoman for the American Optometric Association, weighs in.

Simple Solution

Though there are countless products on the market claiming to wipe streaks away, the AOA recommends the most basic of options: kitchen-sink soap. The best way to clean your glasses, says Dr. Geist, is to run them under warm water and put a tiny drop of dishwashing detergent on the tip of your fingers to create a lather on the lens. Then rinse with warm water, and dry with a clean, soft cotton cloth.

"Everyone uses their shirt cloth—worst thing!" she says. "Your shirttail almost certainly carries dust, and that has the potential of scratching your lens."

Glass vs. Plastic

Of the 69.1 million Americans who bought prescription spectacles last year, most purchased plastic lenses; glass has gone out of fashion as safety concerns have arisen. Unlike that hard surface, plastic is soft and can scratch easily.

Once lenses are scraped up, "there is no way to buff that scratch out," says Dr. Geist. Attempting to clean glasses when dry only exacerbates the problem, since a wet surface is slicker than a dry one. "People breathe on their glasses then grab a Kleenex or paper towel or napkin because they're convenient, but the rough fibers that they're comprised of might leave debris behind," Dr. Geist says. She adds that special microfiber cloths are good for dry touch-ups during the day, but aren't a stand-in for a thorough, soapy cleaning. Neither is your breath.

Reflecting on the Problem

Lenses typically have some form of protective coating and should never come into contact with ammonia, bleach, vinegar or window cleaner. "Those chemicals can break down the coating or just strip them," says Dr. Geist. "You know those bubbles you sometimes see on your lens? Those are caused by 'cleansing' solutions." Avoid the problem by requesting anti-glare and UV coatings that are embedded within the lens, which can cost about $100 more than regular-coated lenses.

Clean Lines

Natural oils from your hands, eyelashes and face can lead to a lot of buildup each day, reducing lenses' effectiveness. Leaving spectacles on a sink or vanity, where hair spray and perfume can fly through the air, adds to the residue. The AOA recommends washing glasses every morning, paying special attention to the frames and earpieces, where hair product and makeup tend to rub off. Whatever you do, don't use the most handy form of water to clean your lenses. "Some people use spit, but don't," urges Dr. Geist. Though dirty glasses won't cause an eye infection, saliva "is not the best hygiene method, and it just won't work very well," she says. Soap, warm water and a dry cloth are all you need, once a day, to keep glasses optimally clean and functional. "I have had patients who say they can't see well, but it turns out it is just the scratches," says Dr. Geist.