When cleaning eyeglasses and sunglasses, it is important to use a material that will not scratch the lenses.  So many items are too abrasive and will damage the lens.  Avoid paper towels, clothing (unless 100% cotton), tissues (leave debris), and napkins.  It is always safest to use materials made of 100% cotton.  I have found baby face cloths to be the most gentle.  They are made for babies, are usually made with 100% cotton, and are extremely soft.  It's handy to keep one stashed in your purse or car at all times.  Damp or dry, they work wonders.