TL;DR
Almost every scratched lens was scratched by its owner wiping dry grit across it. Rinse the lenses under lukewarm running water first, wash them with a tiny drop of lotion-free dish soap and your fingertips, rinse, and dry with a clean microfiber cloth. Keep ammonia, alcohol, glass cleaner, and paper towels away from any lens with an anti-reflective coating.
Why lenses scratch
Modern lenses are plastic, not glass. Plastic is lighter and safer, and it is much softer than glass. Most lenses then carry thin coatings on top: anti-reflective, scratch-resistant, ultraviolet, sometimes anti-fog or blue-light filtering.
Those coatings are microscopically thin. They give a lens its clarity and they are the part that fails first.
The airborne grit that lands on lenses all day is mostly mineral dust, and mineral dust is harder than lens plastic. Wiping a dry lens drags that grit across the surface like sandpaper. That is the whole mechanism behind the fine web of scratches on a two-year-old pair.
A shirt tail is worse, because fabric holds grit and adds its own texture. Paper towels and tissues are worse still, since paper is made of wood fiber and behaves like a very fine abrasive.
How do you clean eyeglass lenses?
Rinse them under lukewarm running water to float off grit, put one small drop of lotion-free dish soap on each lens, rub gently with clean fingertips including the frame and nose pads, rinse thoroughly, shake off the water, and dry with a clean microfiber cloth.
The routine that keeps coatings intact
1. Wash your hands first. Hand oil and lotion transfer straight to the lens.
2. Rinse under lukewarm running water. This is the step people skip and it is the step that prevents scratches. Water carries the grit off before anything touches the surface.
3. Use one drop of dish soap. Plain, lotion-free dish soap. Lotion-added soaps leave a film that smears.
4. Rub gently with fingertips. Both sides of each lens, the frame, the nose pads, and the area where the arms meet the frame -- that is where skin oil and makeup collect.
5. Rinse everything. Soap residue causes streaks.
6. Shake off the water and dry with clean microfiber. A dedicated lens cloth, washed regularly. A dirty microfiber cloth is just a grit delivery system.
Lukewarm water only. Hot water can damage some coatings and can loosen the adhesive holding frames together.
What to keep away from your lenses
Ammonia and glass cleaner. Household glass cleaners commonly contain ammonia, which attacks anti-reflective coatings. This is the most common way people wreck a new pair.
Rubbing alcohol and hand sanitizer. Alcohol strips coatings and can craze plastic. A wipe labeled for eyewear is formulated differently from a generic alcohol wipe.
Acetone and nail polish remover. These dissolve lens plastic outright.
Vinegar and other acids. Not appropriate for coated optical surfaces.
Paper towels, tissues, napkins, and clothing. All abrasive at the scale a coating cares about.
Bleach or any disinfecting spray. Nothing meant for a countertop belongs on a lens.
Your breath plus a shirt. The classic move, and the classic way to grind dust into a coating.
The same coating chemistry applies to sunglasses, which have their own extra complications -- see how to clean sunglasses and polarized lenses. Plastic optical surfaces in general dislike alcohol, which is also why it ruins storage acrylic, as covered in how to clean an acrylic cosmetic organizer.
Why do my glasses look smeared after cleaning?
Smearing usually means residue rather than dirt: lotion-added soap, fabric softener left in a microfiber cloth, hand cream, or a spray that dried on the lens. Wash the lenses with plain lotion-free dish soap and water, rinse thoroughly, and dry with a freshly laundered microfiber cloth washed without softener.
Caring for the cloth and the case
A microfiber cloth works by trapping oil and particles in its fibers, which means it fills up.
Wash lens cloths every week or two in plain detergent with no fabric softener and no dryer sheets. Softener coats the fibers and destroys the cloth. Air dry it, or tumble on low with nothing that sheds lint.
Keep several. One in the case, one at a desk, one in a bag. A cloth that has been rattling around a pocket with keys and coins is carrying grit.
Store glasses in a hard case rather than face down on a surface. Most bad scratches happen off the face, not on it.
Source: American Academy of Ophthalmology consumer guidance on eyewear care
Frames, nose pads, and the parts nobody cleans
The lenses get all the attention and the frame collects most of the grime.
Skin oil, sweat, sunscreen, and makeup build up behind the nose pads and in the hinges. That buildup causes slipping, green marks on skin from some metal frames, and eventually a loose fit.
The soap-and-water wash handles this if you actually rub those areas. For a heavier buildup, a soft toothbrush kept for the purpose works on nose pads and hinges -- gently, and away from the lens surface.
Acetate frames can be wiped with a damp cloth. Do not soak wooden frames, and do not put any frame in hot water. Metal frames tolerate more, but the screws are small and loosen over time.
If a frame is bent or a lens keeps popping out, an optician can usually fix it in a couple of minutes, often at no charge. That is a better outcome than bending it yourself.
What cleaning cannot fix
Scratches are permanent. Nothing polishes a scratch out of a coated lens without removing the coating, and the products that claim to do it generally make the optics worse.
Coating delamination -- the cloudy, crackled look that spreads from the edges -- is also permanent, and it usually comes from heat, harsh chemicals, or age. New lenses are the only fix.
If your vision is blurry with clean lenses, that is a prescription question, not a cleaning question. Book an eye exam. The same boundary applies to contacts, where hygiene rules are stricter still, in how to clean a contact lens case correctly.
FAQ
Can you use glass cleaner on eyeglasses?
No. Most household glass cleaners contain ammonia, which attacks the anti-reflective coating on modern lenses and can cause permanent hazing or crazing. Use lukewarm water with a small drop of lotion-free dish soap, or a spray specifically labeled for coated eyewear.
Why should you rinse glasses before wiping them?
Because airborne dust is mostly mineral grit, and mineral grit is harder than lens plastic. Wiping a dry lens drags that grit across the coating and creates the fine scratches that build up over a year or two. A few seconds under running water floats the grit away first.
Can you clean glasses with rubbing alcohol?
It is risky. Alcohol strips or clouds many lens coatings and can craze plastic lenses over time, and it also attacks the adhesives and finishes on some frames. Wipes sold specifically for eyewear are formulated to be safe. Generic alcohol wipes are not the same product.
How do you get rid of the film on eyeglass lenses?
Wash them with plain lotion-free dish soap and lukewarm water, rubbing gently with your fingertips, then rinse thoroughly and dry with a freshly laundered microfiber cloth. Film is usually residue from lotion-added soap, hand cream, sunscreen, or fabric softener left in a lens cloth.
Can scratches be removed from eyeglass lenses?
No. A scratch is missing material, and any product that claims to buff it out removes coating along with it, which usually makes the optics worse. Some coatings carry a manufacturer warranty for early failure, so ask your optician before assuming you need a whole new pair.
How often should you clean your glasses?
A full soap-and-water wash once a day is reasonable for most people, with a light microfiber wipe between times when the lenses are already dust free. Wash the microfiber cloth every week or two in plain detergent, with no fabric softener and no dryer sheets.
Clear lenses are easier to keep in a home that is not shedding dust everywhere. If keeping up with that is more than you want to take on, get a quote or read more about house cleaning services.