I don't know why people say this. When I wore glasses I cleaned them with my cotton shirts for over a decade and they didn't get scratched up, at all. I don't see how cotton would scratch glass to begin with.
Very few people wear actual glass lenses. They are something like 1-2% of the market from what I can tell. Everyone else wears plastic lenses, which are much lighter and thus more comfortable to wear. Also slightly safer due to much reduced risk of shattering with plastic lenses. I've never even had an optometrist offer glass lenses. I think you'd have to specifically ask for them.
But yeah, dust can also definitely scratch the coatings on glass lenses, too.
Are we still talking about glasses, not contacts right? Because everyone over here (Norway) gets glass lenses in glasses on prescription. They are much better optical quality and not uncomfortable in the slightest, and can be customized to individual vision. Mine have glass from Rodenstock, a long time camera lens supplier but other vendors like Zeiss or Swarowski are common too.
You can always tell if it's glass by tint of PVD coating. Polycarbonate or acrylic lenses can't be coated. Plastic's only advantage is low manufacturing cost.
> You can always tell if it's glass by tint of PVD coating. Polycarbonate or acrylic lenses can't be coated.
This not true. Plastic can absolutely be PVD coated. You can buy cheap sunglasses with PVD mirror coatings on plastic lenses. I’m pretty sure Rodenstock’s own plastic coatings (e.g. “Rodenstock technology Solitaire® Protect Plus 2”) are also a PVD process.
> Plastic's only advantage is low manufacturing cost.
And weight. And shatter resistance. And higher refractive index options.
In USA I've been told by multiple glasses sellers (wrongly, but they believed it) that no companies sell glass lenses anymore. It's apparently rare enough that a lot of stores think it doesn't exist.
They live in an imaginary world where no one ever cleaned glasses until microfiber cloths were widely available.
To clean glasses safely you basically need a soft, clean cloth. Cotton is totally fine. You could get away with a soft clean sponge, too. Or even a soft-ish piece of paper (which is what most disposable lens words are.)
There is lens-cleaning paper (I used to use this in photgraphy), and facial tissue-grade paper.
The latter does tend to scratch over time, if perhaps only slighly, but the damage can accumulate.
I'm on team soft-cotton, with a very-well-worn bandana serving as my usual cleaning material, plastic lenses, no scratches.
Another sin, for glasses, is laying them lens-down, or face-up, on surfaces when not in use. Lens-down of course grinds the lens into whatever is on the surface. Face-up, as you'd wear them, is vulnerable to flipping over (most glasses are top-heavy), so upside down is preferable. Or folded, with the earpieces down and lenses up. In a case is of course preferable to either.
Leaving glasses randomly on chairs, sofas, beds, etc., is also an invitation to catastrophe.
I've lived with people doing many of the above, and their glasses were perpetually scratched and damaged. Given the high cost of a new pair for many of them, this was ... curious.
Most believe whatever marketing material or sponsored "expert" advice is presented to them for "proper care", without actually checking. At least glasses clenaning is a harmless area - people do the same for supplements, diets, and all kinds of health advice too.